Semiconductor light-emitting device Number:6,737,669 from the United States Patent and Trademark Office (PTO) owispatent

Title: Semiconductor light-emitting device

Abstract: A semiconductor light-emitting device has a lower clad layer, an active layer, a p-type GaP layer and an upper clad layer, which are successively formed on an n-type GaAs substrate. The p-type GaP layer has a higher energy position by 0.10 eV than the upper clad layer in the conduction band, which makes it more difficult to let electrons escape from the active layer. This contributes to increase of the probability of radiative recombination between electrons and holes in the active layer, and thereby, luminance of the semiconductor light-emitting device is improved. The p-type GaP layer is effective in a semiconductor light-emitting device having a short wavelength in particular.

Patent Number: 6,737,669 Issued on 05/18/2004 to Nakamura,   et al.

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Inventors:	Nakamura; Junchi (Kashiba, JP), Sasaki; Kazuaki (Osaka, JP)
Assignee:	Sharp Kabushiki Kaisha (Osaka, JP)
Appl. No.:	10/304,710
Filed:	November 27, 2002

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Foreign Application Priority Data

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Nov 27, 2001 [JP]			2001-360936
Oct 04, 2002 [JP]			2002-292557

Current U.S. Class:	257/10 ; 257/103; 257/14; 257/E33.005; 257/E33.027
Current International Class:	H01L 33/00 (20060101)
Field of Search:	257/10,14,103

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References Cited [Referenced By]

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U.S. Patent Documents

	5764672		June 1998		Ukita et al.
	2002/0179923		December 2002		Morita et al.

Foreign Patent Documents

	4-229665		Aug., 1992		JP
	5-335619		Dec., 1993		JP
	8-018102		Jan., 1996		JP
	9-260724		Oct., 1997		JP
	11-087768		Mar., 1999		JP

Primary Examiner: Nelms; David
Assistant Examiner: Ho; Tu-Tu
Attorney, Agent or Firm: Morrison & Foerster LLP

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Claims

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What is claimed is:

1. A semiconductor light-emitting device comprising: a compound semiconductor substrate; a first-conductive-type clad layer formed on the compound semiconductor substrate; an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; a second-conductive-type clad layer formed on the active layer; and a semiconductor layer interposed between the active layer and the first-conductive-type clad layer or the second-conductive-type clad layer, wherein an energy position at a lower end of a conduction band of the semiconductor layer is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second-conductive-type clad layer in a band profile before formation of a junction between the active layer and the semiconductor layer, and a junction between the semiconductor layer and the first-conductive-type clad layer or the second-conductive-type clad layer.

2. A semiconductor light-emitting device comprising: a compound semiconductor substrate; a first-conductive-type clad layer formed on the compound semiconductor substrate; an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; a second-conductive-type clad layer formed on the active layer; and a semiconductor layer interposed between the active layer and the first-conductive-type clad layer or between the active layer and the second-conductive-type clad layer, wherein a highest energy position at a lower end of a conduction band of the semiconductor layer is 0.02 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second-conductive-type clad layer.

3. A semiconductor light-emitting device comprising: a compound semiconductor substrate; a first-conductive-type clad layer formed on the compound semiconductor substrate; an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; a first second-conductive-type clad layer formed on the active layer; a second second-conductive-type clad layer formed on the first second-conductive-type clad layer; and at least one semiconductor layer interposed between the first second-conductive-type clad layer and the second second-conductive-type clad layer, wherein an energy position at a lower end of a conduction band of the semiconductor layer is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second second-conductive-type clad layer in a band profile before formation of a junction between the first second-conductive-type clad layer and the semiconductor layer and a junction between the semiconductor layer and second second-conductive-type clad layer.

4. A semiconductor light-emitting device comprising: a compound semiconductor substrate; a first-conductive-type clad layer formed on the a compound semiconductor substrate; an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; a first second-conductive-type clad layer formed on the active layer; a second second-conductive-type clad layer formed on the first second-conductive-type clad layer; and at least one semiconductor layer interposed between the first second-conductive-type clad layer and the second second-conductive-type clad layer, wherein an energy position at a lower end of a conduction band of the semiconductor layer is 0.02 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second second-conductive-type clad layer.

5. A semiconductor light-emitting device comprising: a compound semiconductor substrate; a first first-conductive-type clad layer formed on the compound semiconductor substrate; a second first-conductive-type clad layer formed on the first first-conductive-type clad layer; at least one semiconductor layer interposed between the first first-conductive-type clad layer and the second first-conductive-type clad layer; an active layer formed on the second first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; and a second-conductive-type clad layer formed on the semiconductor layer, wherein an energy position at a lower end of a conduction band of the semiconductor layer is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the first first-conductive-type clad layer in a band profile before formation of a junction between the first first-conductive-type clad layer and the semiconductor layer and a junction between the semiconductor layer and second first-conductive-type clad layer.

6. A semiconductor light-emitting device comprising: a compound semiconductor substrate; a first first-conductive-type clad layer formed on the compound semiconductor substrate; a second first-conductive-type clad layer formed on the first first-conductive-type clad layer; at least one semiconductor layer interposed between the first first-conductive-type clad layer and the second first-conductive-type clad layer; an active layer formed on the second first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; and a second-conductive-type clad layer formed on the semiconductor layer, wherein an energy position at a lower end of a conduction band of the semiconductor layer is 0.02 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the first first-conductive-type clad layer.

7. The semiconductor light-emitting device as claimed in claim 1, wherein the semiconductor layer is either one of a group consisting of a GaP layer, an Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and an (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer.

8. The semiconductor light-emitting device as claimed in claim 1, wherein the semiconductor layer has a thickness range of 10 .ANG. to 500 .ANG..

9. The semiconductor light-emitting device as claimed in claim 1, wherein the semiconductor layer has a thickness range of 10 .ANG. to 140 .ANG..

10. The semiconductor light-emitting device as claimed in claim 1, wherein the active layer is an SQW active layer or an MQW active layer.

11. The semiconductor light-emitting device as claimed in claim 10, wherein the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and the energy position at the lower end of the conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51).

12. A semiconductor light-emitting device comprising: a compound semiconductor substrate; a first-conductive-type clad layer formed on the compound semiconductor substrate; an active layer formed on the first-conductive-type clad layer; and a second-conductive-type clad layer formed on the active layerm, wherein the active layer is an SQW active layer or an MQW active layer comprised of an AlGaInP-based semiconductor, the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and an energy position at a lower end of a conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band from a vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51).

13. The semiconductor light-emitting device as claimed in claim 12, wherein the barrier layers are either one of a group consisting of a GaP layer, an Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and an (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer.

14. The semiconductor light-emitting device as claimed in claim 1, wherein the semiconductor layer or each of the barrier layers is the second conductive type.

15. The semiconductor light-emitting device as claimed in claim 1, wherein the semiconductor layer or each of the barrier layers has a carrier density of 1.times.10.sup.17 to 5.times.10.sup.18 cm.sup.-3.

16. The semiconductor light-emitting device as claimed in claim 1, wherein the first conductive type is n-type, and the second conductive type is p-type.

17. The semiconductor light-emitting device as claimed in claim 2, wherein the semiconductor layer is either one of a group consisting of a GaP layer, an Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and an (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer.

18. The semiconductor light-emitting device as claimed in claim 2, wherein the semiconductor layer has a thickness range of 10 .ANG. to 500 .ANG..

19. The semiconductor light-emitting device as claimed in claim 2, wherein the semiconductor layer has a thickness range of 10 .ANG. to 140 .ANG..

20. The semiconductor light-emitting device as claimed in claim 2, wherein the active layer is an SQW active layer or an MQW active layer.

21. The semiconductor light-emitting device as claimed in claim 20, wherein the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and the energy position at the lower end of the conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51).

22. The semiconductor light-emitting device as claimed in claim 2, wherein the semiconductor layer or each of the barrier layers is the second conductive type.

23. The semiconductor light-emitting device as claimed in claim 2, wherein the semiconductor layer or each of the barrier layers has a carrier density of 1.times.10.sup.17 to 5.times.10.sup.18 cm.sup.-3.

24. The semiconductor light-emitting device as claimed in claim 2, wherein the first conductive type is n-type, and the second conductive type is p-type.

25. The semiconductor light-emitting device as claimed in claim 3, wherein the semiconductor layer is either one of a group consisting of a GaP layer, an Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and an (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer.

26. The semiconductor light-emitting device as claimed in claim 3, wherein the semiconductor layer has a thickness range of 10 .ANG. to 500 .ANG..

27. The semiconductor light-emitting device as claimed in claim 3, wherein the semiconductor layer has a thickness range of 10 .ANG. to 140 .ANG..

28. The semiconductor light-emitting device as claimed in claim 3, wherein the active layer is an SQW active layer or an MQW active layer.

29. The semiconductor light-emitting device as claimed in claim 28, wherein the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and the energy position at the lower end of the conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51).

30. The semiconductor light-emitting device as claimed in claim 3, wherein the semiconductor layer or each of the barrier layers is the second conductive type.

31. The semiconductor light-emitting device as claimed in claim 3, wherein the semiconductor layer or each of the barrier layers has a carrier density of 1.times.10.sup.17 to 5.times.10.sup.18 cm.sup.-3.

32. The semiconductor light-emitting device as claimed in claim 3, wherein the first conductive type is n-type, and the second conductive type is p-type.

33. The semiconductor light-emitting device as claimed in claim 4, wherein the semiconductor layer is either one of a group consisting of a GaP layer, an Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and an (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer.

34. The semiconductor light-emitting device as claimed in claim 4, wherein the semiconductor layer has a thickness range of 10 .ANG. to 500 .ANG..

35. The semiconductor light-emitting device as claimed in claim 4, wherein the semiconductor layer has a thickness range of 10 .ANG. to 140 .ANG..

36. The semiconductor light-emitting device as claimed in claim 4, wherein the active layer is an SQW active layer or an MQW active layer.

37. The semiconductor light-emitting device as claimed in claim 36, wherein the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and the energy position at the lower end of the conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51).

38. The semiconductor light-emitting device as claimed in claim 4, wherein the semiconductor layer or each of the barrier layers is the second conductive type.

39. The semiconductor light-emitting device as claimed in claim 4, wherein the semiconductor layer or each of the barrier layers has a carrier density of 1.times.10.sup.17 to 5.times.10.sup.18 cm.sup.-3.

40. The semiconductor light-emitting device as claimed in claim 4, wherein the first conductive type is n-type, and the second conductive type is p-type.

41. The semiconductor light-emitting device as claimed in claim 5, wherein the semiconductor layer is either one of a group consisting of a GaP layer, an Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and an (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer.

42. The semiconductor light-emitting device as claimed in claim 5, wherein the semiconductor layer has a thickness range of 10 .ANG. to 500 .ANG..

43. The semiconductor light-emitting device as claimed in claim 5, wherein the semiconductor layer has a thickness range of 10 .ANG. to 140 .ANG..

44. The semiconductor light-emitting device as claimed in claim 5, wherein the active layer is an SQW active layer or an MQW active layer.

45. The semiconductor light-emitting device as claimed in claim 44, wherein the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and the energy position at the lower end of the conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51).

46. The semiconductor light-emitting device as claimed in claim 5, wherein the semiconductor layer or each of the barrier layers is the second conductive type.

47. The semiconductor light-emitting device as claimed in claim 5, wherein the semiconductor layer or each of the barrier layers has a carrier density of 1.times.10.sup.17 to 5.times.10.sup.18 cm.sup.-3.

48. The semiconductor light-emitting device as claimed in claim 5, wherein the first conductive type is n-type, and the second conductive type is p-type.

49. The semiconductor light-emitting device as claimed in claim 6, wherein the semiconductor layer is either one of a group consisting of a GaP layer, an Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and an (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer.

50. The semiconductor light-emitting device as claimed in claim 6, wherein the semiconductor layer has a thickness range of 10 .ANG. to 500 .ANG..

51. The semiconductor light-emitting device as claimed in claim 6, wherein the semiconductor layer has a thickness range of 10 .ANG. to 140 .ANG..

52. The semiconductor light-emitting device as claimed in claim 6, wherein the active layer is an SQW active layer or an MQW active layer.

53. The semiconductor light-emitting device as claimed in claim 52, wherein the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and the energy position at the lower end of the conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51).

54. The semiconductor light-emitting device as claimed in claim 6, wherein the semiconductor layer or each of the barrier layers is the second conductive type.

55. The semiconductor light-emitting device as claimed in claim 6, wherein the semiconductor layer or each of the barrier layers has a carrier density of 1.times.10.sup.17 to 5.times.10.sup.18 cm.sup.-3.

56. The semiconductor light-emitting device as claimed in claim 6, wherein the first conductive type is n-type, and the second conductive type is p-type.

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Description

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BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor light-emitting device, and in particular, to a semiconductor light-emitting device that employs an AlGaInP-based semiconductor in its light-emitting section.

In order to form a high-intensity semiconductor light-emitting device, it is required to increase the luminous efficiency of its active layer, increase the amount of injection current into the active layer and increase the efficiency of taking out the light emitted from the active layer to the outside of the device.

In order to increase the amount of injection current into the light-emitting section, a current diffusion layer and an intermediate layer or the like capable of improving the amount of injection current without increasing the operating voltage are effective. At the same time, it is required to increase the amount of electrons and holes that contribute to radiative recombination by confining the injected current (electrons and holes) without letting it escape. As a means for confining electrons and holes in the light-emitting layer, a double-hetero (hereinafter referred to as "DH") structure is widely used.

In the DH structure, the active layer is held between semiconductor layers that have a bandgap wider than that of the active layer. Thereby, an energy barrier over which the electrons and holes hardly pass is formed on the upper and lower sides of the active layer, and therefore, the DH structure makes it difficult to let electrons and holes escape. This enables the increase of the probability that the electrons and holes may contribute to the radiative recombination.

The DH structure is widely used also for a semiconductor light-emitting device in which an AlGaInP-based semiconductor is employed in the active layer (refer to Japanese Patent Laid-Open Publication No. HEI 5-335619, page 2, paragraph 0003 and Japanese Patent Laid-Open Publication No. HEI 4-229665, page 2, paragraphs 0003 and 0004).

FIG. 10 shows a prior art semiconductor light-emitting device that has the DH structure.

According to the above-mentioned semiconductor light-emitting device, as shown in FIG. 10, a desired buffer layer 102, an n-AlGaInP clad layer 103, an AlGaInP active layer 104, a p-AlGaInP clad layer 105 and A GaP current diffusion layer 106 are successively laminated on an n-GaAs substrate 101. Further, on the GaP current diffusion layer 106 are successively laminated the other layers of a current blocking layer, a protective layer, an intermediate bandgap layer, a protective layer and so on that are not shown. A p-type electrode 107 is formed on the GaP current diffusion layer 106. An n-type electrode 108 is formed under the n-GaAs substrate 101 by vapor deposition. Subsequently, the n-GaAs substrate 101, the p-type electrode 107, the n-type electrode 108 and so on are formed into the desired shapes so that a semiconductor light-emitting device is completed.

In the above-mentioned semiconductor light-emitting device, a semiconductor having a composition of (Al.sub.x G.sub.1-x).sub.y In.sub.1-y P (x.apprxeq.0.7 and y.apprxeq.0.5) is employed for the n-type clad layer 103 and the p-type clad layer 105. However, in the general semiconductor light-emitting device of the AlGaInP-based semiconductor, a semiconductor having a clad layer composition of (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0.7.ltoreq.x.ltoreq.1.0, y.apprxeq.0.5) is often employed.

FIG. 11 shows a band profile in the vicinity of the active layer of the prior art semiconductor light-emitting device.

As shown in FIG. 11, the upper and lower clad layers have a bandgap wider than that of the active layer, and therefore, an energy barrier is formed on both outer sides of the active layer. This arrangement restrains the phenomenon that the electrons and holes injected into the active layer escape from the active layer to the outside, i.e., overflow. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and this allows a high-intensity semiconductor light-emitting device to be obtained.

In the above-mentioned prior art example, the DH structure has been used as a method for confining a large number of electrons and holes injected from the outside of the device in the active layer. However, in a device that has a short wavelength of light emitted from the active layer, the bandgap of the active layer is widened, and the difference in the bandgap between the active layer and the clad layer is reduced.

As described above, if the bandgap difference between the active layer and the clad layer is reduced, then the energy barrier against electrons and holes is reduced. As a result, the effect of confining electrons and holes produced by the clad layer is reduced, and therefore, the electrons and holes easily escape from the active layer. That is, the electrons and holes easily overflow from the active layer. For the above-mentioned reasons, there have been the problems that the luminous efficiency has been reduced in the short-waveform semiconductor light-emitting device and a high-intensity semiconductor light-emitting device has hardly been unable to be obtained.

With regard to electron and hole, it is difficult for hole to overflow since hole has a low mobility, whereas it is easy for electron to overflow since electron has a mobility several tens of times higher than that of hole.

In concrete, with regard to the AlGaInP-based semiconductor light-emitting devices, the overflow does not matter in a device that has an emission wavelength longer than 590 nm, whereas the overflow becomes significant in a device that has an emission wavelength of not greater than 590 nm. This overflow causes a reduction in luminance.

FIG. 12 shows a graph showing the relation between emission wavelength and external quantum efficiency in the semiconductor light-emitting device.

As is apparent from FIG. 12, the overflow of electron becomes particularly significant in the semiconductor light-emitting device that has an emission wavelength equal to or shorter than about 590 nm, and therefore, the luminous efficiency falls with reduced luminance. For the above-mentioned reasons, the luminous efficiency falls in the short-wavelength semiconductor light-emitting device, and it is difficult to obtain a high-intensity semiconductor light-emitting device.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to improve the luminance by increasing the probability of radiative recombination of electrons and holes in the active layer of an AlGaInP-based semiconductor light-emitting device of a short wavelength.

In order to solve the aforementioned object, the present invention provides a semiconductor light-emitting device comprising: a compound semiconductor substrate; a first-conductive-type clad layer formed on the compound semiconductor substrate; an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; a second-conductive-type clad layer formed on the active layer; and a semiconductor layer interposed between the active layer and the first-conductive-type clad layer or the second-conductive-type clad layer, wherein an energy position at a lower end of a conduction band of the semiconductor layer is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second-conductive-type clad layer in a band profile before formation of a junction between the active layer and the semiconductor layer, and a junction between the semiconductor layer and the first-conductive-type clad layer or the second-conductive-type clad layer.

According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the active layer and the first-conductive-type clad layer or between the active layer and the second-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.

In the present specification, the first conductive type means the p-type or the n-type. Moreover, the second conductive type means the n-type when the first conductive type is the p-type, or the second conductive type means the p-type when the first conductive type is the n-type.

The present invention also provides a semiconductor light-emitting device comprising: a compound semiconductor substrate; a first-conductive-type clad layer formed on the compound semiconductor substrate; an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; a second-conductive-type clad layer formed on the active layer; and a semiconductor layer interposed between the active layer and the first-conductive-type clad layer or between the active layer and the second-conductive-type clad layer, wherein a highest energy position at a lower end of a conduction band of the semiconductor layer is 0.02 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second-conductive-type clad layer.

According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the active layer and the first-conductive-type clad layer or between the active layer and the second-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.

The present invention also provides a semiconductor light-emitting device comprising: a compound semiconductor substrate; a first-conductive-type clad layer formed on the compound semiconductor substrate; an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; a first second-conductive-type clad layer formed on the active layer; a second second-conductive-type clad layer formed on the first second-conductive-type clad layer; and at least one semiconductor layer interposed between the first second-conductive-type clad layer and the second second-conductive-type clad layer, wherein an energy position at a lower end of a conduction band of the semiconductor layer is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second second-conductive-type clad layer in a band profile before formation of a junction between the first second-conductive-type clad layer and the semiconductor layer and a junction between the semiconductor layer and second second-conductive-type clad layer.

According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the first second-conductive-type clad layer and the second second-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.

The present invention also provides a semiconductor light-emitting device comprising: a compound semiconductor substrate; a first-conductive-type clad layer formed on the a compound semiconductor substrate; an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; a first second-conductive-type clad layer formed on the active layer; a second second-conductive-type clad layer formed on the first second-conductive-type clad layer; and at least one semiconductor layer interposed between the first second-conductive-type clad layer and the second second-conductive-type clad layer, wherein an energy position at a lower end of a conduction band of the semiconductor layer is 0.02 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second second-conductive-type clad layer.

According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the first second-conductive-type clad layer and the second second-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.

The present invention also provides a semiconductor light-emitting device comprising: a compound semiconductor substrate; a first first-conductive-type clad layer formed on the compound semiconductor substrate; a second first-conductive-type clad layer formed on the first first-conductive-type clad layer; at least one semiconductor layer interposed between the first first-conductive-type clad layer and the second first-conductive-type clad layer; an active layer formed on the second first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; and a second-conductive-type clad layer formed on the semiconductor layer, wherein an energy position at a lower end of a conduction band of the semiconductor layer is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the first first-conductive-type clad layer in a band profile before formation of a junction between the first first-conductive-type clad layer and the semiconductor layer and a junction between the semiconductor layer and second first-conductive-type clad layer.

According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the first first-conductive-type clad layer and the second first-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.

The present invention also provides a semiconductor light-emitting device comprising: a compound semiconductor substrate; a first first-conductive-type clad layer formed on the compound semiconductor substrate; a second first-conductive-type clad layer formed on the first first-conductive-type clad layer; at least one semiconductor layer interposed between the first first-conductive-type clad layer and the second first-conductive-type clad layer; an active layer formed on the second first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; and a second-conductive-type clad layer formed on the semiconductor layer, wherein an energy position at a lower end of a conduction band of the semiconductor layer is 0.02 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the first first-conductive-type clad layer.

According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the first first-conductive-type clad layer and the second first-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.

In the semiconductor light-emitting device of one embodiment, the semiconductor layer is either one of a group consisting of a GaP layer, an Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and an (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer.

In the semiconductor light-emitting device of the above-mentioned embodiment, the semiconductor layer is either one of the GaP layer, the Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and the (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer. Therefore, the overflow of electrons from the active layer can reliably be restrained.

In the semiconductor light-emitting device of one embodiment, the semiconductor layer has a thickness range of 10 .ANG. to 500 .ANG..

In the semiconductor light-emitting device of the above-mentioned embodiment, the thickness of the semiconductor layer is within the range of 10 .ANG. to 500 .ANG.. Therefore, the overflow of electrons from the active layer can reliably be restrained, and crystal defect due to lattice mismatch can be restrained. That is, when the thickness of the semiconductor layer is smaller than 10 .ANG., the overflow of electrons cannot reliably be restrained. When the thickness of the semiconductor layer exceeds 500 .ANG., the crystal defect due to lattice mismatch occurs.

In the semiconductor light-emitting device of one embodiment, the semiconductor layer has a thickness range of 10 .ANG. to 140 .ANG..

Since the layer having lattice mismatch is inserted, wafer warp occurs. The wafer warp significantly occurs when a wafer is thinned by grinding before the wafer obtained after growth is divided into device elements. However, in the semiconductor light-emitting device of the above-mentioned embodiment, the layer thickness is set smaller than 500 .ANG. or, in particular, not greater than 140 .ANG.. Therefore, the wafer warp can reliably be restrained. Accordingly, it is preferable to set the thickness of the semiconductor layer within the range of 10 .ANG. to 140 .ANG..

In the semiconductor light-emitting device of one embodiment, the active layer is an SQW active layer or an MQW active layer.

In the semiconductor light-emitting device of one embodiment, the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and the energy position at the lower end of the conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51).

According to the semiconductor light-emitting device of the above-mentioned embodiment, the energy position at the lower end of the conduction band from the vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51). Therefore, electrons can reliably be confined in the well layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.

The present invention also provides a semiconductor light-emitting device comprising: a compound semiconductor substrate; a first-conductive-type clad layer formed on the compound semiconductor substrate; an active layer formed on the first-conductive-type clad layer; and a second-conductive-type clad layer formed on the active layerm, wherein the active layer is an SQW active layer or an MQW active layer comprised of an AlGaInP-based semiconductor, the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and an energy position at a lower end of a conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band from a vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51).

According to the semiconductor light-emitting device of the above-mentioned construction, the energy position at the lower end of the conduction band from the vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x=0.7, y=0.51). Therefore, the overflow of electrons from the active layer can be restrained by reliably confining the electrons in the well layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.

In the semiconductor light-emitting device of one embodiment, the barrier layers are either one of a group consisting of a GaP layer, an Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and an (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer.

According to the semiconductor light-emitting device of the above-mentioned embodiment, the barrier layers should preferably be either one of the GaP layer, the Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer and the (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (0<x.ltoreq.0.7, 0.65.ltoreq.y<1) layer in terms of reliably restraining the overflow of electrons from the active layer.

In the semiconductor light-emitting device of one embodiment, the semiconductor layer or each of the barrier layers is the second conductive type.

In the semiconductor light-emitting device of one embodiment, the semiconductor layer or each of the barrier layers has a carrier density of 1.times.10.sup.17 to 5.times.10.sup.18 cm.sup.-3.

In the semiconductor light-emitting device of one embodiment, the first conductive type is n-type, and the second conductive type is p-type.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1A is a schematic sectional view showing the construction of a semiconductor light-emitting device according to a first embodiment of the present invention;

FIG. 1B is a view showing one example of a band profile in the vicinity of an active layer of the semiconductor light-emitting device;

FIG. 2A is a schematic sectional view showing the construction of a semiconductor light-emitting device according to a second embodiment of the present invention;

FIG. 2B is a view showing one example of a band profile in the vicinity of an active layer of the semiconductor light-emitting device;

FIG. 3A is a schematic sectional view showing the construction of a semiconductor light-emitting device according to a third embodiment of the present invention;

FIG. 3B is a view showing one example of a band profile in the vicinity of an active layer of the semiconductor light-emitting device;

FIG. 4A is a schematic sectional view showing the construction of a semiconductor light-emitting device according to a fourth embodiment of the present invention;

FIG. 4B is a view showing one example of a band profile in the vicinity of an active layer of the semiconductor light-emitting device;

FIG. 5A is a schematic sectional view showing the construction of a semiconductor light-emitting device according to a fifth embodiment of the present invention;

FIG. 5B is a view showing one example of a band profile in the vicinity of an active layer of the semiconductor light-emitting device;

FIG. 6A is a schematic sectional view showing the construction of a semiconductor light-emitting device according to a sixth embodiment of the present invention;

FIG. 6B is a view showing one example of a band profile in the vicinity of an active layer of the semiconductor light-emitting device;

FIG. 7A is a schematic sectional view showing the construction of a semiconductor light-emitting device according to a seventh embodiment of the present invention;

FIG. 7B is an enlarged view an essential part of FIG. 7A;

FIG. 7C is a view showing one example of a band profile in an active layer of the semiconductor light-emitting device;

FIG. 8A is a schematic sectional view showing the construction of a semiconductor light-emitting device according to an eighth embodiment of the present invention;

FIG. 8B is an enlarged view of an essential part of FIG. 8A;

FIG. 8C is a view showing one example of a band profile in an active layer and in the vicinity of the active layer of the semiconductor light-emitting device;

FIG. 9A is a schematic sectional view showing the construction of a semiconductor light-emitting device according to a ninth embodiment of the present invention;

FIG. 9B is an enlarged view of an essential part of FIG. 9A;

FIG. 9C is a view showing one example of a band profile in an active layer and in the vicinity of the active layer of the semiconductor light-emitting device;

FIG. 10 is a schematic sectional view showing the construction of a prior art semiconductor light-emitting device;

FIG. 11 is a view showing one example of a band profile in the vicinity of an active layer of the prior art semiconductor light-emitting device; and

FIG. 12 is a graph showing relation between an emission wavelength and an external quantum efficiency of the prior art semiconductor light-emitting device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The Present invention will be described in detailed below based on embodiments thereof.

First Embodiment

A light-emitting diode which is a semiconductor light-emitting device according to a first embodiment of the present invention will be described with reference to FIGS. 1A and 1B.

As shown in FIG. 1A, the light-emitting diode is provided with an n-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) lower clad layer 12 serving as one example of the first-conductive-type clad layer, an (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.ltoreq.x.ltoreq.1) active layer 13 serving as one example of the active layer and a p-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) upper clad layer 15 serving as one example of the second-conductive-type clad layer, which are successively formed on an n-type GaAs substrate 11 serving as one example of the compound semiconductor substrate. Then, a p-type GaP layer 14 serving as one example of the semiconductor layer is interposed between the active layer 13 and the upper clad layer 15.

The active layer 13 emits light that has a wavelength of not greater than 590 nm. The highest energy position at the lower end of the conduction band of this p-type GaP layer 14 is 0.02 eV to 1.0 eV higher than the energy position at the lower end of the conduction band of the upper clad layer 15. Moreover, in the band profile before the formation of the junctions of the active layer 13, the p-type GaP layer 14 and the upper clad layer 15, the energy position at the lower end of the conduction band of the p-type GaP layer 14 is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band of the upper clad layer 15.

Moreover, a current diffusion layer 16 is formed on the upper clad layer 15, and a p-type electrode 17 is formed on this current diffusion layer 16. An n-type electrode 18 is formed under the n-type GaAs substrate 11.

FIG. 1B shows one example of a band profile in the vicinity of the active layer 13 in the light-emitting diode of the first embodiment.

The light-emitting diode of the first embodiment has the p-type GaP layer 14 between the active layer 13 and the upper clad layer 15. Before the active layer 13, the p-type GaP layer 14 and the upper clad layer 15 are joined, the energy difference at the lower end of the conduction band between the active layer 13 and the p-type GaP layer 14 is larger than the energy difference at the lower end of the conduction band between the active layer 13 and the upper clad layer 15. Therefore, after the active layer 13, the p-type GaP layer 14 and the upper clad layer 15 are joined, there generates a notch due to energy discontinuity of about 0.3 eV difference between the active layer 13 and the p-type GaP layer 14, where an energy barrier is formed which is about 0.1 eV higher than the lower end Ec of the conduction band of the upper clad layer 15 as shown in FIG. 1B. This energy barrier operates as an energy barrier against the electrons supplied from the lower clad layer 12.

As described above, formation of the notch energy barrier furthermore restrains the overflow of the electrons supplied from the lower clad layer 12 than when the GaP layer 14 does not exist. As a result, there increases the probability of radiative recombination between electrons and holes in the active layer 13, and therefore, the luminance is more increased than that in the prior art shown in FIG. 10.

The fabricating method of the light-emitting diode of the first embodiment will be described below.

First of all, as shown in FIG. 1A, an n-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) lower clad layer 12 (e.g., x==1.0, Si carrier density: 5.times.10.sup.17 cm.sup.-3, thickness: 1.0 .mu.m) and an (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.ltoreq.x.ltoreq.1) active layer 13 (e.g., x=0.30, thickness: 0.3 .mu.m) are successively grown on the n-type GaAs substrate 11.

Subsequently, the p-type GaP layer 14 (thickness: 20 .ANG., carrier density: 1.times.10.sup.17 cm.sup.-3) and the p-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) upper clad layer 15 (e.g., x=1.0, Zn carrier density: 7.times.10.sup.17 cm.sup.-3, thickness: 1.0 .mu.m) are successively grown on the active layer 13. Further, the current diffusion layer 16 is grown on the upper clad layer 15. In this case, the p-type GaP layer 14 has a lattice mismatch of about 3.5% with respect to GaAs. However, since the GaP thickness has a small value of about 20 .ANG., no lattice relaxation occurs. As a result, no such crystal defect as cross hatching occurs.

Then, by using vapor deposition, the p-type electrode 17 (e.g., Au--Zn) is formed on the current diffusion layer 16, and the n-type electrode 18 (e.g., Au--Ge) is formed under the n-type GaAs substrate. The p-type electrode 17 is formed into a circular shape for example, so that a light-emitting diode is completed.

In the first embodiment, the active layer 13 is formed between the lower clad layer 12 and the p-type GaP layer 14. However, it is acceptable to form an SQW active layer or an MQW active layer instead of the active layer 13 between the lower clad layer 12 and the p-type GaP layer 14.

It is also acceptable to successively form a p-type lower clad layer, an active layer and an n-type upper clad layer on a substrate and provide a p-type GaP layer between the p-type lower clad layer and the active layer.

Second Embodiment

A light-emitting diode which is a semiconductor light-emitting device according to a second embodiment of the present invention will be described with reference to FIGS. 2A and 2B.

As shown in FIG. 2A, the light-emitting diode is provided with an n-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) lower clad layer 22 serving as one example of the first-conductive-type clad layer, an (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.ltoreq.x.ltoreq.1) active layer 23 serving as one example of the active layer, a p-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) first upper clad layer 24 serving as one example of the first second-conductive-type clad layer and a p-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) second upper clad layer 26 serving as one example of the second second-conductive-type clad layer, which are successively formed on an n-type GaAs substrate 21 serving as one example of the compound semiconductor substrate. Then, a p-type GaP layer 25 serving as one example of the semiconductor layer is interposed between the first upper clad layer 24 and the second upper clad layer 26.

The active layer 23 emits light that has a wavelength of not greater than 590 nm. The highest energy position at the lower end of the conduction band of this p-type GaP layer 25 is 0.02 eV to 1.0 eV higher than the energy position at the lower end of the conduction band of the second upper clad layer 26. Moreover, in the band profile before the formation of the junctions of the first upper clad layer 24, the p-type GaP layer 25 and the second upper clad layer 26, the energy position at the lower end of the conduction band of the p-type GaP layer 25 is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band of the second upper clad layer 26.

Moreover, a current diffusion layer 27 is formed on the second upper clad layer 26, and a p-type electrode 28 is formed on this current diffusion layer 27. An n-type electrode 29 is formed under the n-type GaAs substrate 21.

FIG. 2B shows one example of the band profile in the vicinity of the active layer 23 of the light-emitting diode of the second embodiment.

The light-emitting diode of the second embodiment has the p-type GaP layer 25 between the first upper clad layer 24 and the second upper clad layer 26. There is energy discontinuity between the first upper clad layer 24 and the p-type GaP layer 25. Therefore, after the first upper clad layer 24 and the p-type GaP layer 25 are joined, there generates a notch due to energy discontinuity of about 0.25 eV difference between the first upper clad layer 24 and the p-type GaP layer 25, where an energy barrier is formed which is about 0.12 eV higher than the lower end Ec of the conduction band of the first upper clad layer 24 as shown in FIG. 2B. This energy barrier operates as an energy barrier against the electrons supplied from the lower clad layer 22.

As described above, due to the energy barrier ascribed to the notch, overflow of the electrons supplied from the lower clad layer 22 can be restrained further than when the p-type GaP layer 25 does not exist. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer 23, and therefore, the luminance increases further than in the prior art shown in FIG. 10.

The fabricating method of the light-emitting diode of the second embodiment will be described below.

First of all, as shown in FIG. 2A, an n-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) lower clad layer 22 (e.g., x=0.7, Si carrier density: 5.times.10.sup.17 cm.sup.-3, thickness: 1.0 .mu.m) and an (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.ltoreq.x.ltoreq.1) active layer 23 (e.g., x=0.40, thickness: 0.4 .mu.m) are successively grown on the n-type GaAs substrate 21.

Subsequently, the p-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) first upper clad layer 24 (e.g., x=0.7, Zn carrier density: 5.times.10.sup.17 cm.sup.-3, thickness: 0.2 .mu.m), the p-type GaP layer 25 (thickness: 40 .ANG., carrier density: 1.times.10.sup.18 cm.sup.-3) and the p-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) second upper clad layer 26 (e.g., x=0.7, Zn carrier density: 5.times.10.sup.17 cm.sup.-3, thickness: 0.7 .mu.m) are successively grown on the active layer 23. Further, the current diffusion layer 27 is grown on the second upper clad layer 26.

Then, the p-type electrode 28 (e.g., Au--Zn) is formed on the current diffusion layer 27, and the n-type electrode 29 (e.g., Au--Ge) is formed under the n-type GaAs substrate 21, each by vapor deposition. The p-type electrode 28 is formed into a circular shape for example, so that a light-emitting diode is completed.

In the second embodiment, one p-type GaP layer 25 is interposed between the first upper clad layer 24 and the second upper clad layer 26. However, it is acceptable to interpose a plurality of p-type GaP layers between the first upper clad layer 24 and the second upper clad layer 26.

It is also acceptable to successively form a first p-type lower clad layer, a second p-type lower clad layer, an active layer and an upper clad layer on a substrate and provide a p-type GaP layer between the first p-type lower clad layer and the second p-type lower clad layer. It is needless to say that a plurality of p-type GaP layers may be provided between the first p-type lower clad layer and the second p-type lower clad layer.

Third Embodiment

A light-emitting diode which is a semiconductor light-emitting device according to a third embodiment of the present invention will be described with reference to FIGS. 3A and 3B.

As shown in FIG. 3A, the light-emitting diode is provided with an n-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) lower clad layer 32 serving as one example of the first-conductive-type clad layer, an (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.ltoreq.x.ltoreq.1) active layer 33 serving as one example of the active layer and a p-type (Al.sub.x Ga.sub.1-x).sub.0.51 In.sub.0.49 P (0.7.ltoreq.x.ltoreq.1) upper clad layer 35 serving as one example of the second-conductive-type clad layer, which are successively formed on an n-type GaAs substrate 31 serving as one example of the compound semiconductor substrate. Then, a p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34 serving as one example of the semiconductor layer is interposed between the active layer 33 and the upper clad layer 35.

The active layer 33 emits light that has a wavelength of not greater than 590 nm. The highest energy position at the lower end of the conduction band of this p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34 is 0.02 eV to 1.0 eV higher than the energy position at the lower end of the conduction band of the upper clad layer 35. Moreover, in the band profile before the formation of the junction between the active layer 33 and the p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34 and the formation of the junction between the p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34 and the upper clad layer 35, the energy position at the lower end of the conduction band of the p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34 is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band of the upper clad layer 35.

Moreover, a current diffusion layer 36 is formed on the upper clad layer 35, and a p-type electrode 37 is formed on this current diffusion layer 36. An n-type electrode 38 is formed under the n-type GaAs substrate 31.

FIG. 3B shows one example of the band profile in the vicinity of the active layer 33 of the light-emitting diode of the third embodiment.

The light-emitting diode of the third embodiment has the p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34 between the active layer 33 and the upper clad layer 35. Before the active layer 33, the p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34 and the upper clad layer 35 are joined, the energy difference at the lower end of the conduction band between the active layer 33 and the p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34 is larger than the energy difference between the active layer 33 and the upper clad layer 35. Therefore, after the active layer 33, the p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34 and the upper clad layer 35 are joined, there generates a notch due to energy discontinuity of about 0.20 eV difference between the active layer 33 and the p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34, where an energy barrier is formed which is about 0.08 eV higher than the lower end Ec of the conduction band of the upper clad layer 35, as shown in FIG. 3B. This energy barrier operates as an energy barrier against the electrons supplied from the lower clad layer 32.

As described above, due to the energy barrier ascribed to the notch, the overflow of the electrons supplied from the lower clad layer 32 can be restrained further than when the p-type Al.sub.x Ga.sub.1-x P (0<x.ltoreq.0.7) layer 34 does not exist. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer 33, and therefore, the luminance increases further than in the prior art shown in FIG. 10.

The fabricating method of the light-emitting diode of the third embodiment wi