NL9001192A - Visible light emitting semiconductor diode - with indium (aluminium) gallium phosphide grown over aluminium gallium arsenide buffer - Google Patents

Abstract

A radiation-emitting semiconductor diode comprises a semiconductor substrate (1) of first conductivity type on which are provided in order a first cladding layer (2) of first conductivity type, an active layer (3) and a second cladding layer (4) of a second conductivity type. The cladding layers comprise In-Al-Ga phosphide (InAlGaP) and the active layer comprises InGaP or InAlGaP. These semiconductor materials each consist of a mixed crystal having two sublattices in which the phosphorus atoms are present on the one sublattice and the atoms of the other elements on the other sublattice. A buffer layer (11) of first conductivity type is interposed between the substrate and the first cladding layer and comprises Al-Ga-arsenide, AlGaAs wherein the Al content has at least a min. value belonging to the band gap of the active layer.

Description

Radiation-emitting semiconductor device and method for its manufacture.

The invention relates to a radiation-emitting semiconductor diode comprising a semiconductor body with a semiconductor substrate of a first conductivity type on which at least successively at least a first containment layer of the first conductivity type, an active layer and a second containment layer of a second conductivity type, wherein the containment layers of indium aluminum galliumphosphide (InAlGaP) and the active layer of indiumgalliumphosphide (InGaP) or indiumaluminiumgalliumphosphide (InAlGaP) as semiconductor material, which semiconductor materials each comprise a mixed crystal with two sublattices where the phosphor atoms are on the one sublattice and the atoms on the one sublattice other sub-lattice, and wherein a buffer layer of the first conductivity type is present between the substrate and the first containment layer. The invention also relates to a method for manufacturing a radiation-emitting semiconductor diode, wherein on a semiconductor substrate of gallium arsenide and of a first conductivity type, successively at least a first retaining layer of indium aluminum gallium phosphide and of an first conductivity type, an active layer of indium galium phosphide and a second containment layer of indium aluminum gallium phosphide and of a second conductivity type, a buffer layer being applied before the application of the first containment layer.

Such radiation-emitting semiconductor diodes, especially when the wavelength of the emission is in the visible part of the spectrum, are - if designed as a diode laser - suitable radiation sources for information processing systems such as laser printers with which information is written and "optical". disc "systems such as Compact Disc (Video) (CD (V)) players or bar code readers where information is read and Digital Optical Recording (DOR) systems where information is written and read. There are also numerous applications in opto-electronic systems for an LED version of such diodes.

Such a radiation-emitting diode and such a method of manufacturing it are known from the article "AlGalnP Double Heterostructure Visible-Light Laser Diodes with aGalnP Active Layer Grown by Metalorganic Vapor Phase Epitaxy" published by IEEE Journal of Quantum Electronics, vol. QE-23, No. 6, June 1987, p. 704. It describes a radiation-emitting layer in which an active layer of InGaP is located on a substrate of n-GaAs between two retaining layers of InAlGaP. The semiconductor materials of these layers each comprise a mixed crystal with two subgrids in which the phosphor atoms are on one and the atoms of the other elements, here In and Ga atoms for the active layer and In, Al and Ga atoms for the confinement layers, are located on the other sub-lattice Between the substrate and the first confinement layer is a buffer layer of GaAs The wavelength of the emission of the di ode is about 670 nm (i.e. the photoluminescence wavelength is about 660 nm (corresponding to a band gap of about 1.88 eV).

A drawback of the known radiation-emitting semiconductor diode is that the experimentally found wavelength of the emission is higher than the theoretically expected: for example for an InGaP active layer, the expected wavelength is about 650 nm, while in practice often about 670 nm or more is found . The same effect also occurs with confinement layers containing InGaAlP where the experimentally found bandgap also lags behind the theoretically expected. The bandgap of both the active layer and the containment layer can be increased by increasing the aluminum content of those layers.

This possibility is limited, in particular, for the containment layers containing indirect semiconductor materials, since the continued addition of aluminum results in an increasingly small increase in the band gap and doping of the containment layers becomes more difficult. As for the active layer, thinning it is also an option, which however makes the production more difficult. It has been found experimentally that when using misoriented substrates, for example (311) or (511) substrates, the experimental bandgap - and therefore also the wavelength of the emission - is (much) closer to the theoretically expected value. However, the use of misoriented substrates is more expensive and has the drawback that it limits the choice of the longitudinal direction of the cavity.

One of the objects of the present invention is to realize a radiation-emitting semiconductor diode - in particular a semiconductor diode laser - which does not have, or at least to a much lesser degree, the aforementioned drawback, and thus combines the lowest possible wavelength of the emission with the highest possible bandgap of the containment layers. Furthermore, it is an object of the present invention to realize a diode with an active layer containing InGaP with a band gap equal to about 1.94 eV which corresponds to a wavelength of about 650 nm for a diode laser (the wavelength in photoluminescence is then about 640 nm). In particular, the invention aims to realize such a diode which emits at a wavelength of 633 nm, which is exactly the wavelength of a Helium-Neon gas laser. Another object of the invention is to provide a simple method of manufacturing such a radiation-emitting semiconductor diode.

According to the invention, a radiation-emitting semiconductor diode of the type described in the preamble is characterized in that the buffer layer contains aluminum gallium arsenide (AlGaAs), the aluminum content having at least a minimum value associated with the band gap of the active layer. The bandgap remaining at the theoretically expected value, it has been found, is caused by an arrangement in the mixed crystals of the retaining layers and the active layer in the (sub) crystal lattice of the III elements. Such an arrangement appears to occur with mixed crystals of various materials and for the materials used here, the arrangement occurs in the 1/2 (111) A planes and resembles the arrangement of the so-called CuPt structure. In addition to the substrate orientation, growth conditions such as the growth temperature have also been shown to influence whether or not this arrangement occurs. Particularly at a relatively high growth temperature, no or at least little ordering occurs, as a result of which the band gap of the applied layer is maximal. However, when the known buffer layer is used, the crystallinity of semiconductor layers of InGaP or InAlGaP manufactured at higher temperatures is deficient, which has a very detrimental effect on the quality of the radiation-emitting semiconductor diode. A buffer layer containing AlGaAs with an aluminum content greater than or equal to a minimum value associated with the active layer bandgap has been found to make it surprisingly possible to apply the InGaP or InAlGaP layers at higher temperatures than usual - and thus with a more disordered distribution of the atoms of the other elements over the other sub-lattice - while still obtaining semiconductor layers with very good morphology and crystallinity. The resulting semiconductor layers therefore have a band gap which corresponds to a more random distribution of the atoms of the other elements over the other sub-lattice. For the semiconductor materials used here, this means that, for example, InO, 49GaO, 51P has a bandgap of approximately 1.85 eV (at a high degree of order) and a bandgap of approximately 1.94 at an almost completely disordered distribution corresponding to an emission wavelength from about 680 to 650 nm. For example In0.50A ^ 0.10Ga0.25 axis bandgap (at almost complete disorder) about 2.05 eV and for InQ 59½ 30Ga0 20 axis at eV 'which are higher values than are found for the same materials with an ordered structure. For example, for an InGaP active layer with a band gap of about 1.88 eV, the minimum aluminum content of the buffer layer is about 6 atomic percent. For an InGaP active layer with a band gap of approximately 1.92 eV, the minimum aluminum content of the buffer layer is approximately 9 atomic percent. At the top, no limitation has been found for the aluminum content of the AlGaAs buffer layer. Preferably, however, the aluminum content is chosen to be less than 100 atomic percent since pure AlAs is quite hygroscopic, which can lead to problems with exposure of the cleaving surfaces to be formed to the air. In order to ensure good electrical conductivity, the aluminum content can be further limited to those levels where a relatively low specific resistance is still possible. No lower limit has been found with regard to the thickness of the buffer layer: buffer layers with a thickness of 6 ° A and an aluminum content of 20% were also excellent. Good results have been obtained with a buffer layer thickness between 0.1 and 1 µm. It should be noted that the device from the article "Fabrication and optical characterization of first order DFB InGaP / AlGalnP laser structures at 639 nm published in Electronics Letters, 26th April 1990, vol. 26, no. 9, p. 614 AlGaAs layer is located between a DH (= Double Hetero) structure and the substrate, however, it is not a radiation-emitting diode since there is no pn junction present and no aluminum content is given or implied In addition, the stated wavelength of the emission of the InGaP, namely a photoluminescence wavelength of 670 nm (ie the bandgap corresponds to 1.85 eV) that the InGaP contains a very highly ordered distribution of the atoms of the other elements over the other sub-lattice (in the case of a diode laser version the wavelength of the emission is about 680 nm) In the radiation-emitting semiconductor diode according to the invention, a (substantially perfectly oriented) (001) sub street which is an important advantage as previously explained. A substrate of gallium arsene is preferably used, but other substrates, for example a silicon substrate, can also be used. In a favorable embodiment, the substrate contains gallium arsenide, which is provided with a conductive layer on the underside, successively comprises an intermediate layer of indium gallium phosphide or aluminum gallium arsenide and a contact layer of gallium arsenide, which layers are of the second conductivity type, on the top retaining layer, and comprises the semiconductor body a mesa-shaped strip adjacent to its surface which contains at least the contact layer and which is covered with another conductive layer which extends beyond the mesa-shaped strip and forms a barrier transition with an underlying layer therebetween. In this embodiment, the current is very well limited to the active area located below the mesa-shaped strip, which promotes a low starting current. This embodiment has the additional advantage that the radiation-emitting semiconductor diode has a simple structure and is particularly easy to manufacture: the other conductive layer can be applied without a mask step. To achieve the lowest possible wavelength, use is preferably made of an active layer containing a multi-quantum well structure with well layers of InGaP and barrier layers of InAlGaP. With a radiation-emitting semiconductor diode according to the invention, there are no very thin layers to already obtain a significant increase in the wavelength: well and barrier layers with a thickness between about 4 and 6 nm are already sufficiently thin and are relatively easy to manufacture. Thus, radiation-emitting semiconductor diodes according to the invention have been produced which have an emission wavelength of 633 nm, which is equal to the wavelength of a He-Ne gas laser, by forming the active layer with 8 well layers of InGaP with a thickness of about 5 nm separated by barrier layers about 4 nm thick. The containment layers formed a so-called SCH (= Separate Confinement Hetero) structure with aluminum contents of 25 at. % for the separate confinement layers and 35 at. % for the containment layers.

A method of manufacturing a radiation-emitting semiconductor diode according to the invention is characterized in that the semiconductor material for the buffer layer is chosen aluminum gallium arsenide with an aluminum content that is at least equal to a minimum value associated with the bandgap of the active layer and a growth temperature greater than 700 ° C. This promotes the disorder of the distribution of the atoms of the elements other than phosphor over the sub lattice in which these elements are located, thereby obtaining diodes with the desired properties. Due to the relatively high temperature, semiconductor layer structure with excellent properties such as good morphology, good crystallinity and good interfaces are obtained. Preferably, a growth temperature of at least 730 ° C is selected, while the best results are obtained using MOVPE as a growth technique at a temperature of about 760 ° C. At a growth temperature of about 730 ° C, a minimum value of the aluminum content of the buffer layer should be about 6 percent by weight. For 760 ° C, the minimum aluminum content is about 9 atomic percent. Preferably, a (001) substrate is chosen as the substrate and the ratio of the quantities of III and V elements offered during the application of the semiconductor layers is chosen between approximately 100 and 400. These V / III ratios have proven favorable for obtaining of the greatest possible disorder in the mixed crystals of the semiconductor layers formed.

The invention will now be further elucidated with reference to two exemplary embodiments and the accompanying drawing, in which figure 1 shows in cross-section an embodiment of a radiation-emitting semiconductor diode according to the invention; Figures 2 and 3 show in cross-section the radiation-emitting semiconductor diode of Figure 1 in successive stages of manufacture; Figure 4 shows the light output versus the current of a radiation-emitting semiconductor diode according to the invention which ate 9. % aluminum contained in the active layer and manufactured at a growth temperature of 700 ° C; Figure 5 shows the light output versus the current of a radiation-emitting semiconductor diode according to the invention which ate 0. % contains aluminum in the active layer and is manufactured at a growth temperature of 760 ° C; Figure 6 shows the half-value width of the 004 reflection in a double crystal recording of an indium aluminum gallium phosphide-containing semiconductor layer grown on an aluminum gallium arsenide-containing buffer layer as a function of the aluminum content of the buffer layer-wherein the layers have grown at a temperature of 760 ° C;

The figures are schematic and not drawn to scale, in particular the dimensions in the thickness direction have been exaggerated for the sake of clarity. Corresponding parts are generally designated by the same reference numerals in the various examples. Semiconductor regions of the same conductivity type are generally shaded in the same direction.

Figure 1 shows in cross section a first embodiment of a radiation-emitting semiconductor diode according to the invention. The semiconductor diode comprises a semiconductor body with a substrate region 1 provided with a connecting conductor 8 of a former, here the n, conductivity type and in this example consisting of single crystalline gallium arsenide. A semiconductor layer structure is provided thereon, which includes a first containment layer 2 of n-InAlGaP, an active layer 3 of InGaP, and a second containment layer 4 of p-InAlGaP. In these mixed crystals, the phosphor atoms are on one sub-lattice and the atoms of the other elements are on another sub-lattice. According to the invention, between the substrate region 1 and the first containment layer 2, there is a buffer layer 11 of aluminum gallium arsenide (AlGaAs), the aluminum content of which has at least a minimum value associated with the bandgap of the InGaP active layer. In this example, the bandgap of a (thick) InGaP layer is about 1.92 eV and the minimum aluminum content of the buffer layer is about 9 atomic percent.

In this example, an aluminum content of the buffer layer of about 20 atomic percent was used. As a result, the layers present above the buffer layer 11 can be provided with properties required for a properly functioning diode, while they are applied at a relatively high growth temperature: for example, these layers can have excellent morphology, good crystalline properties, among other things, as shown by a small line width. in a double crystal recording and excellent optical properties such as an intense and narrow luminescence peak. Due to the relatively high temperature when the semiconductor layers are applied above the buffer layer 11, the distribution of the III elements over the other sub-lattice has the most disorderly character possible, as a result of which the band gap of the active layer (distribution of In and Ga atoms) of the InGaP is relatively large, for example 1.92 eV, and therefore the wavelength is relatively low. The same applies to the retaining layers 2.4 of InAlGaP, which, for example, has an aluminum content of 35 at. % have a band gap of about 2.3 eV, so that the resulting diode has a low temperature dependence of the starting current. In this example, the containment layers 2 and 4 contain 0.8 µm thick partial layers 2 'and 4' containing InQ ^ AIq -jcjGaQ ^ P and 25 nm thick partial layers 2 "and 4" (the so-called Separate Confinement layers) containing InQ 5Alo, 25GaO, 25P, while the active layer 3 comprises a multi-quantum well structure containing eight 5nm thick well layers of InGaP separated from each other by seven 4nm thick of InQ ^ A1q 25Gao 25p · Despite this, relatively large thickness of the quantum well layers, the radiation-emitting semiconductor diode according to the invention has a particularly low emission wavelength of, in this example, 633 nm and is an attractive alternative to Helium-neon gas lasers that emit at the same wavelength. Helium-neon gas lasers are much more expensive and robust and also use more energy than diode lasers. The fact that the quantum well layers may be relatively thick is due to the aforementioned disordered distribution and the associated relatively large bandgap. The AlGaAs-containing buffer layer in this example contains 20 atomic percent aluminum. In this example, the thickness of the buffer layer was 0.1 µm. Above the second containment layer 4 there is an intermediate layer 5, of the opposite, here the p, conductivity type and here of indium gallium phosphide and a contact layer 6 also of the opposite, here therefore the p, conductivity type, and here of gallium arsenide which is a mesa-shaped strip 12. A conductive layer 7 is provided over this mesa-shaped strip, which, with the intermediate layer 5 below it, forms a barrier-forming transition outside the mesa-shaped strip 12. As a result, little or no current flows through the regions 13 and 14 in the semiconductor body next to the mesa-shaped strip 12 below a certain voltage when the conductive layers 7 and 8 are incorporated in a circuit. Within the semiconductor body there is a strip-shaped region 13, of which the mesa-shaped strip 12 forms part, within which there is a p-n junction which, at a sufficiently high current in the forward direction, leads to emission of electromagnetic radiation. Since the conductive layer 7 forms a good electrical contact with the contact layer 6, the area 13 forms a preferred path for the electrical current. In this example, the radiation-emitting semiconductor diode is designed as a diode laser of the gain-guided type. This means that the emission is coherent at a sufficiently high current. In connection with the design as a diode laser, the mesa-shaped strip 12 is bounded perpendicular to the longitudinal direction by two mutually parallel mirror surfaces lying in the plane of the drawing, which coincide with natural splitting surfaces of the crystal from which the semiconductor body is formed. As a result, a cavity for the radiation generated is formed within the fuel-shaped region 13 in the active layer 3. The diode laser of this example is easy to manufacture and has, in addition to a very low emission wavelength, a low temperature dependence of the starting current and thus a high maximum operating temperature. In this example, the following compositions, dopings and thicknesses have been used for the various semiconductor layers.

Low Semiconductor Type Doping Thickness Bandgap Concent. (pm) (at / cm3) 1 GaAs (substrate) N 2x10 ^ 8 350 1.4 11 Al0 2Ga0 8AS N 2x1018 0.1 1.7 2 '^ 5 ^ 35 ^ 0.15 ^ s 2lt1 ° 18 °' 8 2'3 2 InQ 5 ^ 0 25Ga0 25P ^ 2x10 ^ 8 0.025 2.15 3 In0.5Ga0.5p (8x): 5nm + InQf5Al0f25Ga0f25P (7x) 4nm 4 "InO, 5AlO, 25GaO, 25P P 4x1017 0.025 2, 15 4 'InO, 5AlO, 35GaO, 15P P 4x1017 0.8 2.3 5 In05Ga0f5P P 1x1018 0.1 1.9 6 GaAs P 2x1018 0.5 1.4

The width of the mesa-shaped strip 12 is about 7 µm. The conductive layer 8 on the substrate 1 in this example is a gold-germanium-nickel layer, with a thickness of about 1000 ° A. The conductive layer 7 in this example is a platinum, a tantalum and a gold layer with a thickness of about 1000, about 500 and about 2500 ° A, respectively.

The described radiation-emitting semiconductor diode is manufactured according to the invention as follows (see Figures 2 and 3). The starting material is a (001) substrate 1 of single crystalline n-type gallium arsenide with a doping concentration of 2x10 atoms per cm8 and a thickness of, for example, 350 µm. After polishing and etching the surface that has the (001) orientation, it is subsequently grown successively from the gas phase using OMVPE (= Organo Metalic Vapor Phase Epitaxy): a 0.5 pra layer 11 of the n-conductivity type, whereby according to the invention aluminum gallium arsenide with an aluminum content having at least a minimum value associated with the active layer bandgap is selected and a growth temperature of at least about 700 ° C is selected.

For the growth temperature of about 760 ° C chosen here, an aluminum content of the buffer layer must be chosen which is at least about 9 atomic percent. In this example, an aluminum content of about 20 atomic percent is chosen. The subsequent semiconductor layers are applied at the same relatively high temperature of about 760 ° C. This has the advantage, among other things, that the temperature does not have to be switched, which simplifies the method and improves the quality of the interfaces between two successive semiconductor layers. The latter has the advantage that the III elements of the subsequent layers are distributed as disorderly as possible over the relevant sub-grid, so that the band gap of those layers is as large as possible. For the doping concentration, the buffer layer 11 in this example becomes about 2 × 10 8 atoms per cm 8. At a V / III ratio of between 100 and 400, a 0.8 µm thick layer 2 'of n-type InQ ^ AIq 3c; GaQ ^ P with a doping concentration of 2x10 ^ 8 at / cm8, a 25 µm thick, is successively applied. nm thick layer 2 "of n-type InQ [jAIq 25Ga0 25P with a doping concentration of about 18 x 2x10 atoms per cm", an active layer 3 containing eight 5nm thick layers of InQ 4gGa0 51P alternating with seven 4 nm thick layers of InQ jAIq 25Gao 25p ^ evat> a 25nm thick layer 4 "of p-type InQ jAIq 25Gao 25p with a doping concentration of about 1 17 1 1 * 3 4x10 atoms per cm, a 0.8 µm thick layer 4 'of p-type InQ c; A1q 35GaQ with a doping concentration of about 1 17 r 1 o 4x10 atoms per cm, a 0.08 pra thick layer 5 of p-type 18

InQ 4gGaQ 5iP with a doping concentration of 1x10 atoms per 1 cm 1 cm, and a 0.5 µm thick layer 6 of p-type GaAs with a doping of about 1x10 atoms per cm. A 1 µm thick masking layer 10 is applied thereon, for example of photoresist in the form of a strip whose longitudinal axis is perpendicular to the plane of the drawing of Figure 2, which contains a schematic cross-section perpendicular to the longitudinal direction of the resulting structure. Then, in the semiconductor layer structure of Figure 2, a mesa-shaped strip 12 is etched (see Figure 3) with the GaAs contact layer 6 removed using an etchant containing NH3, H2O2 and ^ 0 in the ratio 2: 1: 50, whose etching rate at room temperature is about 0.7 pm / min. The underlying In0 50Ga0 50P intermediate layer 5 acts as an etching stop layer. After removing the mask 10 and after the structure thus obtained has been cleaned, a conductive layer 8 is applied to the substrate 1 by, for example, sputtering, for example consisting of a gold-germanium-nickel layer with a thickness of approximately 1000 ° A (see figure 1).

Finally, for example, with the same technique, a conductive layer 7 is applied over the top of the structure, for example consisting of a platinum, a tantalum and a gold layer, the thickness of which is approximately 1000, approximately 500 and approximately 2500 ° A, respectively. After splitting, the individual radiation-emitting semiconductor diodes - in this case, diode lasers of the gain-guided type - are available for final assembly. For further details, reference is also made to a simultaneously filed Dutch patent application by the applicant, designated PHN 13,336. The aforementioned advantages of a relatively high growth temperature, in this example about 760 ° C, are illustrated with reference to Figures 4 and 5.

Figure 4 shows the light output (P) versus the current (I) through a radiation-emitting semiconductor diode that ate 9. % aluminum in the about 0.1 μια thick active layer 3 of InAlGaP, the AlGaAs buffer layer of which contains about 25 atomic percent aluminum, the containment layers 2 and 4 of InAlGaP at about 35 at. % aluminum and manufactured at a growth temperature of 700 ° C. Curves 41, 42 and 43 represent the P-I characteristic at 20, 40 and 50 ° C, respectively. Figure 5 shows the light output (P) versus the current (I) for a radiation-emitting semiconductor diode according to the invention, the structure of which corresponds to that of the diode of Figure 4. The only differences concern the aluminum content of the active layer 3, that ate zero here. %, and the fact that the diode of Figure 5 is manufactured at a growth temperature of 760 ° C. Curves 51, 52, 53, 54 and 55 represent the P-I characteristic at 20, 40, 60, 80 and 90 ° C, respectively. For both the diode of Figure 4 and that of Figure 5, the emission wavelength was about 650 nm. Comparison of the characteristics of figure 5 with that of figure 4 shows that the former are much more favorable: the starting currents at 20 ° C (curves 51 and 41) are approximately the same size, but the starting current in figure 4 increases much more with increasing temperature then in figure 5. In figure 4 a starting current of 120 mA (curve 43) is already reached at 50 ° C, in figure 5 that (curve 55) is only the case at 90 ° C. Thus, the radiation-emitting semiconductor diodes of Figure 5 have - at substantially the same wavelength as the diodes of Figure 4, namely about 650 nm - a much higher maximum operating temperature than that of Figure 4. This equation confirms that the presence of an AlGaAs-containing buffer layer with an aluminum content of at least about 9 at. % makes it possible to increase the growth temperature with a favorable effect to 760 ° C: a favorable consequence is in particular the relatively low wavelength of the emission, which here is about 650 nm for an InGaP-containing active layer, which corresponds to a photoluminescence wavelength of about 640 nm (Eg = 1.94 eV). Furthermore, it appears that the application of aluminum in the active layer, while the growth temperature is kept at a usual value, does not constitute an equivalent possibility to lower the wave spring of the emission. Admittedly, in this manner, at an aluminum content of the active layer of 9 at. % also reaches a laser wavelength of 650 nm, however the P-I characteristics of such diodes are much less favorable. The influence of the aluminum content of the buffer layer on the crystal quality of a layer grown on it is shown in figure 6.

Figure 6 shows the half value width Δω of the 004 reflection in a double crystal recording of an indium gallium phosphide containing semiconductor layer grown on an aluminum gallium arsenide containing buffer layer as a function of the aluminum content x of the buffer layer. While a (001) GaAs substrate was used as substrate. The growth temperature was 760 ° C. The dotted curve 61 shows the variation of the half-value width Δω in bgsec as a function of the aluminum content x in at. % of the buffer layer. Figure 6 shows that the crystal quality of such an InGaP-containing semiconductor layer is greatly improved when the aluminum content of the buffer layer increases from about 8 to 9 at. %. A similar result as in Figure 6 was found for a growth temperature of about 730 ° C: for 0 and 5.6 atomic percent aluminum in the buffer layer, an infinitely wide reflection was observed here, and for an aluminum content of 6.5 atomic percent or higher, a narrow reflection observed. This means that for this growth temperature to which an InGaP bandgap of approximately 1.88 eV belongs, the minimum aluminum content of the buffer layer is approximately 6 atomic percent. As noted previously, for practical reasons, a buffer layer containing less than 100 atomic percent aluminum is preferred.

The invention is not limited to the exemplary embodiments given, since many modifications and variations are possible for the skilled person within the scope of the invention. For example, compositions of the selected semiconductor materials other than those mentioned in the example may be used: radiation-emitting semiconductor diodes having an active layer containing InAlGaP may also be used. The conductor types can also be replaced (at the same time) by their opposite ones. Regarding the maximum growth temperature, it is noted that although at 790 ° C an even more disordered distribution is found than at about 760 ° C, at 790 ° C problems arose with the morphology of the semiconductor layers. The aluminum content of the buffer layer used here was about 25 at. %. Optimization of the other growing conditions and accurate determination of the minimum aluminum content of the buffer layer at growing temperatures higher than 760 ° C

provide an indication of the maximum growth temperature at which the method according to the invention can be applied.

Depending on the application, an LED version or a laser version of a radiation-emitting semiconductor diode according to the invention can be chosen. Within the laser version, both a gain-guided and an index-guided structure can be applied. Finally, it should be noted that the methods of applying the semiconductor layers used in the exemplary embodiments may also be other than the MOVPE technique. In addition to MOVPE, MOMBE (= Metal Organic Molecular Beam Epitaxy), MBE (= Molecular Beam Epitaxy) or VPE (= Vapor Phase Epitaxy) can also be used.

Claims (14)

A radiation-emitting semiconductor diode comprising a semiconductor body with a semiconductor substrate of a first conductivity type on which there are successively at least a first containment layer of the first conductivity type, an active layer, and a second containment layer of a second conductivity type, the containment layers of indium aluminum gallium phosphospide (InAlGaP) and contain the active layer indium gallium phosphide (InGaP) or indium aluminum gallium phospide (InAlGaP) as semiconductor material, the semiconductor materials each comprising a mixed crystal with two subgrids, the phosphor atoms being on one sublattice and the atoms of the other elements being on the other sublattice and wherein a buffer layer of the first conductivity type is present between the substrate and the first containment layer, characterized in that the buffer layer contains aluminum gallium arsenide (AlGaAs), the aluminum content of the buffer layer being at least one in the band gap of the acti eve has a low minimum value. Radiation-emitting semiconductor diode according to claim 1, characterized in that the minimum aluminum content of the buffer layer is about 6 atomic percent and the band gap of the In0 49Ga0 51p active 1 & a9 is about 1.88 eV. The radiation-emitting semiconductor diode according to claim 1, characterized in that the minimum aluminum content of the buffer layer is about 9 atomic percent and the band gap of the In0 49Ga0 51P act; * eve laa9 is about 1.92 eV. Radiation-emitting semiconductor diode according to any one of the preceding claims, characterized in that the thickness of the buffer layer is at least the thickness of a rona layer. Radiation-emitting semiconductor diode according to any one of the preceding claims, characterized in that the thickness of the buffer layer is about 0.1 to 1 µm. The radiation-emitting semiconductor diode according to any one of the preceding claims, wherein the substrate contains gallium arsenide, characterized in that the crystal orientation of the substrate is (001). orientation. A radiation-emitting semiconductor diode according to any one of the preceding claims, characterized in that the substrate contains gallium arsenide and is provided with a conductive layer on the underside, and an intermediate layer of indium gallium phosphide or aluminum gallium arsenide and a contact layer of gallium arsenide are successively deposited on the top confinement layer. , which layers are of the second conductivity type, and the semiconductor body comprises a surface adjacent mesa-shaped strip containing at least the contact layer and covered with another conductive layer extending beyond the mesa-shaped strip and beyond a barrier transition forms with an underlying layer. Radiation-emitting semiconductor diode according to any one of the preceding claims, characterized in that the active layer contains a multiquantum-well structure with well layers of indium gallium phosphide and with barrier layers of indium aluminum gallium phosphospide. The radiation-emitting semiconductor diode according to claim 7, characterized in that the indium gallium phosphide well layers have a thickness between about 4 and 6 nm. The radiation-emitting semiconductor diode according to claim 8, characterized in that the active layer contains 8 well layers of about 5 nm thickness separated by barrier layers of about 4 nm thickness, while the containment layers each have one active layer-bordering partial layer with, like the barrier layers, an aluminum content of about 0.25 and, incidentally, an aluminum content of about 0.35. The method of manufacturing a radiation-emitting semiconductor diode according to claim 1, wherein on a semiconductor substrate of gallium arsenide and of a first conductivity type successively at least a first containment layer of indium aluminum gallium phosphide and of a first conductivity type, an active layer of indium galium phosphide and a second containment layer of indium aluminum gallium phosphide and of a second conductivity type are applied, wherein a buffer layer is applied before the application of the first retaining layer, characterized in that the semiconductor material for the buffer layer is aluminum gallium arsenide with an aluminum content that has at least a minimum value associated with the bandgap of the active layer and a growth temperature of greater than 700 ° C is chosen. A method according to claim 11, characterized in that a growth temperature of at least about 730 ° C is selected and an aluminum content for the buffer layer of at least about 6 atomic percent is selected. A method according to claim 11 or 12, characterized in that a growth temperature of at least about 760 ° C is selected and an aluminum content for the buffer layer of at least about 9 atomic percent is selected. A method according to claim 11, 12 or 13, wherein the technique for applying the layers lying on the substrate is the MOVPE technique, characterized in that as substrate a (001) substrate, a growth temperature of approximately 760 ° C and a V / III ratio ranging from about 100 to 400 are selected.