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.

Description:
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 x G 1-x ) y In 1-y P (x≈0.7 and y≈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 x Ga 1-x ) y In 1-y P (0.7≦x≦1.0, y≈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 x Ga 1-x P (0&lt;x≦0.7) layer and an (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;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 x Ga 1-x P (0&lt;x≦0.7) layer and the (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;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 Å to 500 Å. 
     In the semiconductor light-emitting device of the above-mentioned embodiment, the thickness of the semiconductor layer is within the range of 10 Å to 500 Å. 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 Å, the overflow of electrons cannot reliably be restrained. When the thickness of the semiconductor layer exceeds 500 Å, 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 Å to 140 Å. 
     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 Å or, in particular, not greater than 140 Å. 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 Å to 140 Å. 
     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 x Ga 1-x ) y In 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 x Ga 1-x ) y In 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 x Ga 1-x ) y In 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 x Ga 1-x ) y In 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 x Ga 1-x P (0&lt;x≦0.7) layer and an (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;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 x Ga 1-x P (0&lt;x≦0.7) layer and the (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;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 1×10 17  to 5×10 18  cm −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 x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  12  serving as one example of the first-conductive-type clad layer, an (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  13  serving as one example of the active layer and a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦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.  1 B. 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 x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  12  (e.g., x==1.0, Si carrier density: 5×10 17  cm −3 , thickness: 1.0 μm) and an (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  13  (e.g., x=0.30, thickness: 0.3 μm) are successively grown on the n-type GaAs substrate  11 . 
     Subsequently, the p-type GaP layer  14  (thickness: 20 Å, carrier density: 1×10 17  cm −3 ) and the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) upper clad layer  15  (e.g., x=1.0, Zn carrier density: 7×10 17  cm −3 , thickness: 1.0 μm) 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 Å, 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 x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  22  serving as one example of the first-conductive-type clad layer, an (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  23  serving as one example of the active layer, a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) first upper clad layer  24  serving as one example of the first second-conductive-type clad layer and a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦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.  2 B. 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 x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  22  (e.g., x=0.7, Si carrier density: 5×10 17  cm −3 , thickness: 1.0 μm) and an (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  23  (e.g., x=0.40, thickness: 0.4 μm) are successively grown on the n-type GaAs substrate  21 . 
     Subsequently, the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) first upper clad layer  24  (e.g., x=0.7, Zn carrier density: 5×10 17  cm −3 , thickness: 0.2 μm), the p-type GaP layer  25  (thickness: 40 Å, carrier density: 1×10 18  cm −3 ) and the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) second upper clad layer  26  (e.g., x=0.7, Zn carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) 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 x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  32  serving as one example of the first-conductive-type clad layer, an (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  33  serving as one example of the active layer and a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦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 x Ga 1-x P (0&lt;x≦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 x Ga 1-x P (0&lt;x≦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 x Ga 1-x P (0&lt;x≦0.7) layer  34  and the formation of the junction between the p-type Al x Ga 1-x P (0&lt;x≦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 x Ga 1-x P (0&lt;x≦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 x Ga 1-x P (0&lt;x≦0.7) layer  34  between the active layer  33  and the upper clad layer  35 . Before the active layer  33 , the p-type Al x Ga 1-x P (0&lt;x≦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 x Ga 1-x P (0&lt;x≦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 x Ga 1-x P (0&lt;x≦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 x Ga 1-x P (0&lt;x≦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.  3 B. 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 x Ga 1-x P (0&lt;x≦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 will be described below. 
     First of all, as shown in FIG. 3A, the n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  32  (e.g., x=0.9, Si carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) and the (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  33  (e.g., x=0.35, thickness: 0.5 μm) are successively grown on the n-type GaAs substrate  31 . 
     Subsequently, the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  34  (e.g., x=0.20, thickness: 50 Å, carrier density: 2×10 18  cm −3 ) and the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) upper clad layer  35  (e.g., x=0.8, Zn carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) are successively grown on the active layer  33 . Further, the current diffusion layer  36  is grown on the upper clad layer  35 . 
     Then, the p-type electrode  37  (e.g., Au—Zn) is formed on the current diffusion layer  36 , and the n-type electrode  38  (e.g., Au—Ge) is formed under the n-type GaAs substrate  31 , each by vapor deposition. The p-type electrode  37  is formed into a circular shape for example, so that a light-emitting diode is completed. 
     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 Al x Ga 1-x P (0&lt;x≦0.7) layer between the p-type lower clad layer and the active layer. 
     Fourth Embodiment 
     A light-emitting diode which is a semiconductor light-emitting device according to a fourth embodiment of the present invention will be described with reference to FIGS. 4A and 4B. 
     As shown in FIG. 4A, the light-emitting diode is provided with an n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  42  serving as one example of the first-conductive-type clad layer, an (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  43  serving as one example of the active layer and a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) first upper clad layer  44  serving as one example of the first second-conductive-type clad layer and a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) second upper clad layer  46  serving as one example of the second second-conductive-type clad layer, which are successively formed on an n-type GaAs substrate  41  serving as one example of the compound semiconductor substrate. Then, a p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  45  serving as one example of the semiconductor layer is interposed between the first upper clad layer  44  and the second upper clad layer  46 . 
     The active layer  43  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 x Ga 1-x P (0&lt;x≦0.7) layer  45  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  46 . Moreover, in the band profile before the formation of the junctions of the first upper clad layer  44 , the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  45  and the second upper clad layer, the energy position at the lower end of the conduction band of the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  45  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  46 . 
     Moreover, a current diffusion layer  47  is formed on the second upper clad layer  46 , and a p-type electrode  48  is formed on this current diffusion layer  47 . An n-type electrode  49  is formed under the n-type GaAs substrate  41 . 
     FIG. 4B shows one example of the band profile in the vicinity of the active layer  43  of the light-emitting diode of the fourth embodiment. 
     The light-emitting diode of the fourth embodiment has the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  45  between the first upper clad layer  44  and the second upper clad layer  46 . There is energy discontinuity between the first upper clad layer  44  and the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  45 . Therefore, after the first upper clad layer  44  and the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  45  are joined, there generates a notch due to energy discontinuity of about 0.07 eV difference between the first upper clad layer  44  and the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  45 , where an energy barrier is formed which is about 0.03 eV higher than the lower end Ec of the conduction band of the upper clad layer  44 , as shown in FIG.  4 B. 
     This energy barrier operates as an energy barrier against the electrons supplied from the lower clad layer  42 . 
     As described above, due to the energy barrier ascribed to the notch, the overflow of the electrons supplied from the lower clad layer  42  can be restrained further than when the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  45  does not exist. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer  43 , 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 fourth embodiment will be described below. 
     First of all, as shown in FIG. 4A, the n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  42  (e.g., x=1.0, Si carrier density: 5×10 17  cm −3 , thickness: 1.0 μm) and the (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  43  (e.g., x=0.45, thickness: 0.3 μm) are successively grown on the n-type GaAs substrate  41 . 
     Subsequently, the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) first upper clad layer  44  (e.g., x=0.9, Zn carrier density: 5×10 17  cm −3 , thickness: 0.1 μm), the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  45  (e.g., x=0.60, thickness: 80 Å, carrier density: 4×10 17  cm −3 ) and the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) second upper clad layer  46  (e.g., x=0.9, Zn carrier density: 5×10 17  cm −3 , thickness: 1.5 μm) are successively grown on the active layer  43 . Further, the current diffusion layer  47  is grown on the second upper clad layer  46 . 
     Then, the p-type electrode  48  (e.g., Au—Zn) is formed on the current diffusion layer  47 , and the n-type electrode  49  (e.g., Au—Ge) is formed under the n-type GaAs substrate  41 , each by vapor deposition. The p-type electrode  48  is formed into a circular shape for example, so that a light-emitting diode is completed. 
     In the fourth embodiment, one p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  45  is interposed between the first upper clad layer  44  and the second upper clad layer  46 . However, it is acceptable to interpose a plurality of p-type Al xGa 1-x P (0&lt;x≦0.7) layers between the first upper clad layer  44  and the second upper clad layer  46 . 
     Although the active layer  43  is formed between the lower clad layer  42  and the first upper clad layer  44 , it is acceptable to form an SQW active layer or an MQW active layer between the lower clad layer  42  and the first upper clad layer  44  in place of the active layer  43 . 
     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 Al x Ga 1-x P (0&lt;x≦0.7) 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 Al x Ga 1-x P (0&lt;x≦0.7) layers may be provided between the first p-type lower clad layer and the second p-type lower clad layer. 
     Fifth Embodiment 
     A light-emitting diode which is a semiconductor light-emitting device according to a fifth embodiment of the present invention will be described with reference to FIGS. 5A and 5B. 
     As shown in FIG. 5A, the light-emitting diode is provided with an n-type (Al x Ga 1-x P) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  52  serving as one example of the first-conductive-type clad layer, an (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  53  serving as one example of the active layer and a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) upper clad layer  55  serving as one example of the second-conductive-type clad layer, which are successively formed on an n-type GaAs substrate  51  serving as one example of the compound semiconductor substrate. Then, a p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  serving as one example of the semiconductor layer is interposed between the active layer  53  and the upper clad layer  55 . 
     The active layer  53  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 x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  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  55 . Moreover, in the band profile before the formation of the junctions of the active layer  53 , the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  and the upper clad layer  55 , the energy position at the lower end of the conduction band of the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  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  55 . 
     A current diffusion layer  56  is formed on the upper clad layer  55 , and a p-type electrode  57  is formed on this current diffusion layer  56 . An n-type electrode  58  is formed under the n-type GaAs substrate  51 . 
     FIG. 5B shows one example of the band profile in the vicinity of the active layer  53  of the light-emitting diode of the fifth embodiment. 
     The light-emitting diode of the fifth embodiment has the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  between the active layer  53  and the upper clad layer  55 . Before the active layer  53 , the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  and the upper clad layer  55  are joined, the energy difference at the lower end of the conduction band between the active layer  53  and the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  is larger than the energy difference between the active layer  53  and the upper clad layer  55 . Therefore, after the active layer  53 , the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  and the upper clad layer  55  are joined, there generates a notch due to energy discontinuity of about 0.20 eV difference between the active layer  53  and the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54 , 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  55 , as shown in FIG.  5 B. This energy barrier operates as an energy barrier against the electrons supplied from the lower clad layer  52 . 
     As described above, due to the energy barrier ascribed to the notch, the overflow of the electrons supplied from the lower clad layer  52  can be restrained further than when the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  does not exist. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer  53 , 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 fifth embodiment of the present invention will be described below. 
     First of all, as shown in FIG. 5A, the n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  52  (e.g., x=0.9, Si carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) and the (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  53  (e.g., x=0.35, thickness: 0.5 μm) are successively grown on the n-type GaAs substrate  51 . 
     Subsequently, the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  (e.g., x=0.20, y=0.05, thickness: 50 Å, carrier density: 3×10 17  cm −3 ) and the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) upper clad layer  55  (e.g., x=0.8, Zn carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) are successively grown on the active layer  53 . Further, the current diffusion layer  56  is grown on the upper clad layer  55 . 
     Then, the p-type electrode  57  (e.g., Au—Zn) is formed on the current diffusion layer  56 , and the n-type electrode  58  (e.g., Au—Ge) is formed under the n-type GaAs substrate  51 , each by vapor deposition. The p-type electrode  57  is formed into a circular shape for example, so that a light-emitting diode is completed. 
     In the fifth embodiment, the active layer  53  is formed between the lower clad layer  52  and the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54 . However, it is acceptable to form an SQW active layer or an MQW active layer between the lower clad layer  52  and the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  54  instead of forming the active layer  53 . 
     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 (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer between the p-type lower clad layer and the active layer. 
     Sixth Embodiment 
     A light-emitting diode which is a semiconductor light-emitting device according to a sixth embodiment of the present invention will be described with reference to FIGS. 6A and 6B. 
     As shown in FIG. 6A, the light-emitting diode is provided with an n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  62  serving as one example of the first-conductive-type clad layer, an (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  63  serving as one example of the active layer, a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) first upper clad layer  64  serving as one example of the first second-conductive-type clad layer and a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) second upper clad layer  66  serving as one example of the second second-conductive-type clad layer, which are successively formed on an n-type GaAs substrate  61  serving as one example of the compound semiconductor substrate. Then, a p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65  serving as one example of the semiconductor layer is interposed between the first upper clad layer  64  and the second upper clad layer  66 . 
     The active layer  63  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 x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65  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  66 . Moreover, in the band profile before the formation of the junctions of the first upper clad layer  64 , the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65  and the second upper clad layer  66 , the energy position at the lower end of the conduction band of the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65  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  66 . 
     A current diffusion layer  67  is formed on the second upper clad layer  66 , and a p-type electrode  68  is formed on this current diffusion layer  67 . An n-type electrode  69  is formed under the n-type GaAs substrate  61 . 
     FIG. 6B shows one example of the band profile in the vicinity of the active layer  63  of the light-emitting diode of the sixth embodiment. 
     The light-emitting diode of the sixth embodiment has the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65  between the first upper clad layer  64  and the second upper clad layer  66 . There is energy discontinuity between the first upper clad layer  64  and the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65 . Therefore, after the first upper clad layer  64  and the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65  are joined, there generates a notch due to energy discontinuity of about 0.05 eV difference between the first upper clad layer  64  and the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65 , where an energy barrier is formed which is about 0.02 eV higher than the lower end Ec of the conduction band of the first upper clad layer  64 , as shown in FIG.  6 B. This energy barrier operates as an energy barrier against the electrons supplied from the lower clad layer  62 . 
     As described above, due to the energy barrier ascribed to the notch, the overflow of the electrons supplied from the lower clad layer  62  can be restrained further than when the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65  does not exist. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer  63 , 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 sixth embodiment will be described below. 
     First of all, as shown in FIG. 6A, the n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  62  (e.g., x=1.0, Si carrier density: 5×10 17  cm −3 , thickness: 1.0 μm), the (Al x Ga 1-x ) 0.51 In 0.49 P (0≦x≦1) active layer  63  (e.g., x=0.45, thickness: 0.3 μm) and the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) first upper clad layer  64  (e.g., x=0.9, Zn carrier density: 5×10 17  cm −3 , thickness: 0.1 μm) are successively grown on the n-type GaAs substrate  61 . 
     Subsequently, the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65  (e.g., x=0.60, y=0.30, thickness: 150 Å, carrier density: 8×10 17  cm −3 ) is formed on the first upper clad layer  64 . 
     Further, the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) second upper clad layer  66  (e.g., x=0.9, Zn carrier density: 5×10 17  cm −3 , thickness: 1.5 μm) is grown on the p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65 , and the current diffusion layer  67  is grown on the second upper clad layer  66 . 
     Then, the p-type electrode  68  (e.g., Au—Zn) is formed on the current diffusion layer  67 , and the n-type electrode  69  (e.g., Au—Ge) is formed under the n-type GaAs substrate  31 , each by vapor deposition. The p-type electrode  68  is formed into a circular shape for example, so that a light-emitting diode is completed. 
     In the sixth embodiment, one p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layer  65  is interposed between the first upper clad layer  64  and the second upper clad layer  66 . However, it is acceptable to interpose a plurality of p-type (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layers between the first upper clad layer  64  and the second upper clad layer  66 . 
     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 (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) 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 (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layers may be provided between the first p-type lower clad layer and the second p-type lower clad layer. 
     Seventh Embodiment 
     A light-emitting diode which is a semiconductor light-emitting device according to a seventh embodiment of the present invention will be described with reference to FIGS. 7A,  7 B and  7 C. 
     FIG. 7A is a schematic sectional view of the light-emitting diode, and FIG. 7B is an enlarged view of the inside of the circle b of FIG.  7 A. 
     As shown in FIG. 7A, the light-emitting diode is provided with an n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  72  serving as one example of the first-conductive-type clad layer, an MQW active layer  73  serving as one example of the active layer and a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) upper clad layer  74  serving as one example of the second-conductive-type clad layer, which are successively formed on an n-type GaAs substrate  71  serving as one example of the compound semiconductor substrate. A current diffusion layer  75  is formed on the upper clad layer  74 , and a p-type electrode  76  is formed on this current diffusion layer  75 . An n-type electrode  77  is formed under the n-type GaAs substrate  71 . 
     As shown in FIG. 7B, the MQW active layer  73  is constructed of an (Al x Ga 1-x ) y In 1-y P (x=0.1, y=0.8) barrier layer  73   a  and an (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) well layer  73   b  and emits light that has a wavelength of not greater than 590 nm. The energy position at the lower end of the conduction band from the vacuum level in all the layers of the barrier layer  73   a  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 the (Al x Ga 1-x ) y In 1-y P (x=0.7, y=0.51). 
     FIG. 7C shows one example of the band profile in the active layer  73  of the light-emitting diode of the seventh embodiment. 
     The light-emitting diode of the seventh embodiment employs the (Al x Ga 1-x ) y In 1-y P (x=0.1, y=0.8) barrier layer  73   a . The energy difference at the lower end of the conduction band between this barrier layer  73   a  and the well layer  73   b  is larger than that between the normally employed barrier layer of (Al x Ga 1-x ) y In 1-y P (x=0.7, y=0.51) and the well layer  73   b . Therefore, an energy barrier of about 0.08 eV generates between the normally employed barrier layer and the well layer, whereas, in the seventh embodiment, an energy barrier of about 0.25 eV generates between the barrier layer  73   a  and the well layer  73   b  as shown in FIG.  7 C. This energy barrier operates as an energy barrier against the electrons supplied from the lower clad layer  72 . 
     As described above, due to the energy barrier of about 0.25 eV difference between the barrier layer  73   a  and the well layer  73   b , confinement of the electrons supplied from the lower clad layer  72  into the well layer  73   b  is intensified, by which the overflow of electrons from the MQW active layer  73  can be restrained. As a result, there increases the probability of radiative recombination of electrons and holes in the MQW active layer  73 , 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 seventh embodiment will be described below. 
     First of all, as shown in FIG. 7A, the n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  72  (e.g., x=0.9, Si carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) is grown on the n-type GaAs substrate  71 , and the MQW active layer  73  is grown on the lower clad layer  72 . This MQW active layer  73  is constructed by alternately growing the (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) barrier layer  73   a  (e.g., x=0.1, y=0.8) and the (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) well layer  73   b  (e.g., x=0.4, y=0.4) in a plurality of layers (e.g., five well layers  73   b  and six barrier layers  73   a ). 
     Subsequently, the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) upper clad layer  74  (e.g., x=0.8, Zn carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) is grown on the MQW active layer  73 , and the current diffusion layer  75  is grown on the upper clad layer  74 . 
     Then, the p-type electrode  76  (e.g., Au—Zn) is formed on the current diffusion layer  75 , the n-type electrode  77  (e.g., Au—Ge) is formed under the n-type GaAs substrate  71 , each by vapor deposition. The p-type electrode  76  is formed into a circular shape for example, so that a light-emitting diode is completed. 
     In the seventh embodiment, the energy position at the lower end of the conduction band from the vacuum level in all the layers of the barrier layer  73   a  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 the (Al x Ga 1-x ) y In 1-y P (x=0.7, y=0.51). However, the energy position at the lower end of the conduction band from the vacuum level in a part of the barrier layers  73   a  may be 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 the (Al x Ga 1-x ) y In 1-y P (x=0.7, y=0.51). 
     Moreover, the effect of increasing the luminance can be obtained similarly to the seventh embodiment also by employing a barrier layer constructed of either one of, for example, GaP, Al x Ga 1-x P (0&lt;x≦0.7) and (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) in place of the barrier layer  73   a.    
     It is also acceptable to successively form a p-type lower clad layer, the MQW active layer  73  and an n-type upper clad layer on a substrate. 
     If the active layer of the MQW structure has an SQW structure instead, the effect of increasing the luminance can be obtained similarly to the seventh embodiment. 
     When the barrier layer or the well layer of the MQW structure is p-type, the effect of increasing the luminance can be obtained similarly to this embodiment. 
     Eighth Embodiment 
     A light-emitting diode which is a semiconductor light-emitting device according to a eighth embodiment of the present invention will be described with reference to FIGS. 8A,  8 B and  8 C. 
     FIG. 8A is a schematic sectional view of the light-emitting diode, and FIG. 8B is an enlarged view of the inside of the circle b of FIG.  8 A. 
     As shown in FIG. 8A, the light-emitting diode is provided with an n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  82  serving as one example of the first-conductive-type clad layer, an SQW active layer  83  serving as one example of the active layer and a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) upper clad layer  85  serving as one example of the second-conductive-type clad layer, which are successively formed on an n-type GaAs substrate  81  serving as one example of the compound semiconductor substrate. Then, a p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  84  serving as one example of the semiconductor layer is interposed between the SQW active layer  83  and the upper clad layer  85 . 
     The SQW active layer  83  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 x Ga 1-x P (0&lt;x≦0.7) layer  84  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  85 . Moreover, in the band profile before the formation of the junctions of the SQW active layer  83 , the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  84  and the upper clad layer  85 , the energy position at the lower end of the conduction band of the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  84  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  85 . 
     A current diffusion layer  86  is formed on the upper clad layer  85 , and a p-type electrode  87  is formed on this current diffusion layer  86 . An n-type electrode  88  is formed under the n-type GaAs substrate  81 . 
     As shown in FIG. 8B, the SQW active layer  83  is constructed of an (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) barrier layer  83   a  serving as one example of the barrier layer, an (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) well layer  83   b  serving as one example of the well layer and an (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) layer serving as one example of the barrier layer. 
     FIG. 8C shows one example of the band profile in the SQW active layer  83  and in the vicinity of the SQW active layer  83  of the light-emitting diode of the eighth embodiment. 
     In the light-emitting diode of the eighth embodiment, the AlGaP layer  84  is formed between the barrier layer  83   a  located on the upper side in FIG.  8 B and the upper clad layer  85 . Before the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  84  and the upper clad  85  are joined, the energy difference at the lower end of the conduction band between the barrier layer  83   a  located on the upper side in FIG.  8 B and the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  84  is larger than the energy difference at the lower end of the conduction band between the barrier layer  83   a  and the upper clad layer  85 . Therefore, only an energy barrier of 0.05 eV is formed between the well layer  83   a  located on the upper side in FIG.  8 B and the upper clad layer  85  if the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  84  does not exist. However, if the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  84  is formed as shown in FIG. 8C, then an energy barrier, which is about 0.08 eV higher than the energy barrier due to the upper clad layer  85 , occurs. This energy barrier operates as an energy barrier against the electrons supplied from the lower clad layer  82 . 
     As described above, due to the energy barrier between the well layer  83   a  located on the upper side in FIG.  8 B and the upper clad layer  85 , the overflow of the electrons supplied from the lower clad layer  82  can be restrained further than when the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  84  does not exist. As a result, there increases the probability of radiative recombination of electrons and holes in the SQW active layer  83 , 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 eighth embodiment will be described below. 
     First of all, as shown in FIG. 8A, the n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  82  (e.g., x=0.9, Si carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) is grown on the n-type GaAs substrate  81 , and the SQW active layer  83  is grown on the lower clad layer  82 . This SQW active layer  83  is constructed of two (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) barrier layers  83   a  (e.g., x=0.55, y=0.5) and one (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) well layer  83   b  (e.g., x=0.45, y=0.45). 
     Subsequently, the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  84  (e.g., x=0.4, thickness: 250 Å, carrier density: 2×10 17  cm −3 ) and the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) upper clad layer  85  (e.g., x=0.8, Zn carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) are successively grown on the SQW active layer  83 . Further, the current diffusion layer  86  is grown on the upper clad layer  85 . 
     Then, the p-type electrode  87  (e.g., Au—Zn) is formed on the current diffusion layer  86 , and the n-type electrode  88  (e.g., Au—Ge) is formed under the n-type GaAs substrate  81 , each by vapor deposition. The p-type electrode  87  is formed into a circular shape for example, so that a light-emitting diode is completed. 
     Moreover, the effect of increasing the luminance can be obtained similarly to the eighth embodiment also by employing a semiconductor layer constructed of, for example, GaP or (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) in place of the p-type Al x Ga 1-x P (0&lt;x≦0.7) layer  84 . 
     If the active layer of the SQW structure has an MQW structure instead, the effect of increasing the luminance can be obtained similarly to the eighth embodiment. 
     It is also acceptable to employ a barrier layer constructed of either one of, for example, GaP, Al x Ga 1-x P (0&lt;x≦0.7) and (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) in place of the barrier layer  83   a.    
     Ninth Embodiment 
     A light-emitting diode which is a semiconductor light-emitting device according to a ninth embodiment of the present invention will be described with reference to FIGS. 9A,  9 B and  9 C. 
     FIG. 9A is a schematic sectional view of the light-emitting diode, and FIG. 9B is an enlarged view of the inside of the circle b of FIG.  9 A. 
     As shown in FIG. 7A, the light-emitting diode is provided with an n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  92  serving as one example of the first-conductive-type clad layer, an SQW active layer  93  serving as one example of the active layer, a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) first upper clad layer  94  serving as one example of the first second-conductive-type clad layer, and a p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) second upper clad layer  96  serving as one example of the second second-conductive-type clad layer, which are successively formed on an n-type GaAs substrate  91  serving as one example of the compound semiconductor substrate. Then, a p-type GaP layer  95  serving as one example of the semiconductor layer is interposed between the first upper clad layer  94  and the second upper clad layer  96 . 
     The highest energy position at the lower end of the conduction band of this p-type GaP layer  95  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  96 . Moreover, in the band profile before the formation of the junctions of the first upper clad layer  94 , the p-type GaP layer  95  and the second upper clad layer  96 , the energy position at the lower end of the conduction band of the p-type GaP layer  95  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  96 . 
     A current diffusion layer  97  is formed on the second upper clad layer  96 , and a p-type electrode  98  is formed on this current diffusion layer  97 . An n-type electrode  99  is formed under the n-type GaAs substrate  91 . 
     As shown in FIG. 9B, the SQW active layer  93  is constructed of an (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) barrier layer  93   a  serving as one example of the barrier layer, an (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) well layer  93   b  serving as one example of the well layer, and an (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) barrier layer  93   a  serving as one example of the barrier layer. Then, the SQW active layer  93  emits light that has a wavelength of not greater than 590 nm. 
     FIG. 9C shows one example of the band profile in the SQW active layer  93  and in the vicinity of the SQW active layer  93  of the light-emitting diode of the ninth embodiment. 
     In the light-emitting diode of the ninth embodiment, the p-type GaP layer  95  is provided between the first upper clad layer  94  and the second upper clad layer  96 . Before the p-type GaP layer  95  and the second upper clad layer  96  are joined, the energy difference between the lower end of the conduction band of the p-type GaP layer  95  and the lower end of the conduction band of the second upper clad layer  96  is large. Therefore, when the p-type GaP layer  95  and the second upper clad layer  96  are joined, an energy barrier generates between the first upper clad layer  94  and the second upper clad layer  96 . The energy barrier due to the p-type GaP layer  95  is about 0.12 eV higher than the energy barrier due to the upper clad layer  96 , as shown in FIG.  9 C. This energy barrier operates as an energy barrier against the electrons supplied from the lower clad layer  92 . 
     As described above, due to the energy barrier between the first upper clad layer  94  and the second upper clad layer  96 , the overflow of the electrons supplied from the lower clad layer  92  can be restrained further than when the p-type GaP layer  95  does not exist. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer  93 , 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 ninth embodiment will be described below. 
     First of all, as shown in FIG. 9A, the n-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) lower clad layer  92  (e.g., x=0.9, Si carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) is grown on the n-type GaAs substrate  91 , and the SQW active layer  93  is grown on the lower clad layer  92 . This SQW active layer  93  is constructed of two (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) barrier layers  93   a  (e.g., x=0.60, y=0.5) and one (Al x Ga 1-x ) y In 1-y P (0≦x≦1.0, 0≦y≦1.0) well layer  93   b.    
     Subsequently, the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) first upper clad layer  94  (e.g., x=0.9, Zn carrier density: 4×10 17  cm −3 , thickness: 0.7 μm), the p-type GaP layer  95  (thickness: 60 Å, carrier density: 5×10 17  cm −3 ) and the p-type (Al x Ga 1-x ) 0.51 In 0.49 P (0.7≦x≦1) second upper clad layer  96  (e.g., x=0.8, Zn carrier density: 5×10 17  cm −3 , thickness: 0.7 μm) are successively grown on the SQW active layer  93 . Further, the current diffusion layer  97  is grown on the second upper clad layer  96 . 
     Then, the p-type electrode  98  (e.g., Au—Zn) is formed on the current diffusion layer  97 , and the n-type electrode  99  (e.g., Au—Ge) is formed under the n-type GaAs substrate  91 , each by vapor deposition. The p-type electrode  98  is formed into a circular shape for example, so that a light-emitting diode is completed. 
     The effect of increasing the luminance can be obtained similarly to the ninth embodiment also by employing a semiconductor layer constructed of, for example, Al x Ga 1-x P (0&lt;x≦0.7) or (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y≦1) in place of the p-type GaP layer  95 ,. 
     If the active layer of the SQW structure had an MQW structure instead, the effect of increasing the luminance was able to be obtained similarly to the ninth embodiment. 
     It is also acceptable to employ a barrier layer constructed of either one of, for example, GaP, Al x Ga 1-x P (0&lt;x≦0.7) and (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) in place of the barrier layer  93   a.    
     In the aforementioned first through ninth embodiments, there are the descriptions of the growth methods, electrode materials, electrode shapes, device configurations and so on. However, the present invention is limited to none of them and is able to be applied to all the AlGaInP-based semiconductor light-emitting devices, each of which has the DH structure where the active layer is held between the clad layers. Moreover, the present invention can similarly be applied to any such structure that the portions through which currents flow are limited or currents are blocked or constricted. 
     In the semiconductor light-emitting device of the aforementioned embodiments, if each of the semiconductor layers, i.e., the GaP layers  14 ,  25  and  95 , the Al x Ga 1-x P (0&lt;x≦0.7) layers  34 ,  45  and  84  and the (Al x Ga 1-x ) y In 1-y P (0&lt;x≦0.7, 0.65≦y&lt;1) layers  54  and  65  has a thickness within a range of 10 Å to 500 Å, then the overflow of the electrons from the active layer can reliably be restrained, and the crystal defect due to lattice mismatch can be restrained. 
     Furthermore, if each of the semiconductor layers has a thickness within a range of 10 Å to 140 Å, then the occurrence of wafer warp ascribed to the insertion of the layer that has lattice mismatch can reliably be restrained. 
     As is apparent from the above, the semiconductor light-emitting device of the present invention can restrain the overflow of the electrons injected into the active layer, and therefore, there increases the probability of radiative recombination of electrons and holes in the active layer. As a result, a high-intensity semiconductor light-emitting device can be obtained. 
     The invention being thus described, it will be obvious that the invention may be varied in many ways. Such variations are not be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.