Compound semiconductor substrate and method for manufacturing the same

Abstract

To provide a compound semiconductor substrate which has an AlGaInP quaternary light-emitting layer and, when applied to a light-emitting device, can improve the luminance life characteristics when power is applied, and a method for manufacturing the same.SOLUTION: A compound semiconductor substrate includes a quaternary light-emitting layer, which is formed by sequentially stacking on an n-type GaP substrate at least an n-type cladding layer, an active layer, and a p-type cladding layer, each made of (AlxGa1-x)yIn1-yP (where 0≤x≤1, 0≤y≤1), and a p-type GaP layer serving as a window layer, which is stacked on a second main surface of the quaternary light-emitting layer opposite to a first main surface facing the n-type GaP substrate, and the active layer has a p-type impurity concentration of 9×1015 (Atoms / cm3) or less and an n-type impurity concentration of 7×1015 (Atoms / cm3) or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a compound semiconductor substrate and a method for manufacturing the compound semiconductor substrate. [Background technology]

[0002] Light-emitting devices are known in which a light-emitting layer and a window layer (or current spreading layer) are formed on a GaAs substrate. For example, a light-emitting layer having a double heterostructure made of a quaternary mixed crystal of AlGaInP and a window layer made of GaP are formed on a GaAs substrate.

[0003] This GaP window layer can be fabricated by forming a relatively thin window layer on the light-emitting layer side by metal organic vapor phase epitaxy (hereinafter simply referred to as MOVPE), and then forming a relatively thick window layer by hydride vapor phase epitaxy (hereinafter simply referred to as HVPE).

[0004] Although providing a window layer on one side of the light-emitting layer is effective in improving light-emitting efficiency, it is known that providing a window layer on the other side, i.e., above and below the light-emitting layer, improves external quantum efficiency and achieves higher brightness. In this case, the light-absorbing GaAs substrate can be removed and replaced with a light-transmitting GaP substrate or by laminating a GaP layer by crystal growth.

[0005] However, the total film thickness formed by MOVPE is at most about 10 μm, and if the GaAs substrate were removed in this state, the wafer would not have the mechanical strength required for industrial processing. Therefore, it is rational to grow a thick GaP layer before removing the GaAs substrate to give the wafer (also called an epitaxial wafer or epi-wafer) mechanical strength, so that the GaP layer can function both as a window layer for extracting light and as a strength plate.

[0006] When forming such a thick GaP layer by crystal growth, the GaP layer must be at least 20 μm thick to have sufficient mechanical strength for industrial processing. However, crystal growth of a GaP layer with a thickness of 20 μm or more takes several to several tens of hours.

[0007] Furthermore, the temperature required to grow the GaP layer formed by HVPE is generally higher than the temperature required to grow the light-emitting layer, and the light-emitting layer is exposed to the temperature during MOVPE growth or higher for a long period of time, i.e., it is subjected to a large thermal history.

[0008] On the other hand, the p-type cladding layer is doped with p-type dopants such as Mg and Zn, and when heated, these p-type dopants diffuse thermodynamically, and also diffuse into the active layer.

[0009] Dopant diffusion occurs not only due to thermal history but also due to the passage of current. For example, in p / n junction elements, a potential difference occurs, and p-type dopants that have been ionized to p-type diffuse into regions where p-type dopants are scarce or into n-type dopant regions during current flow. In principle, n-type dopants also undergo the same phenomenon as p-type dopants, but the diffusion of n-type dopants during current flow is much smaller than that of p-type dopants.

[0010] The p-type dopant diffused into the active layer is prone to forming defects, which form when a current is applied, resulting in a decrease in carrier injection efficiency, an increase in light absorption, and a decrease in brightness.

[0011] As a method for suppressing the diffusion of p-type dopants such as Mg and Zn into such an active layer, for example, Patent Document 1 discloses setting the carrier concentration within an appropriate range, providing an undoped layer (hereinafter also referred to as a non-doped layer) that is not doped with a dopant, and using two or more types of dopants.

[0012] Furthermore, Patent Document 2 discloses a method of doping a p-type intermediate layer between a p-type cladding layer and a p-type window layer with a p-type dopant and an n-type dopant, and describes doping with an n-type dopant in an amount of 0.1 to 140% of the p-type dopant. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-151240 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-166399 Summary of the Invention [Problem to be solved by the invention]

[0014] However, the methods described in Patent Documents 1 and 2 have limitations in epitaxial manufacturing, which requires a severe thermal history. If the doping concentration of the p-type cladding layer is drastically reduced in order to suppress the diffusion of the p-type dopant into the active layer, or if the thickness of the non-doped layer in Patent Document 1 or the p-type intermediate layer in Patent Document 2 is increased, the electrical characteristics will deteriorate.

[0015] Furthermore, Patent Documents 1 and 2 do not take into account the effect of n-type dopants, although their effect is smaller than that of p-type dopants. In practice, even when the diffusion of p-type dopants into the active layer is sufficiently suppressed, there are occasional cases in which the luminance life characteristics during life tests of light-emitting devices do not improve as expected. This is because, even if the diffusion of p-type dopants into the active layer is sufficiently suppressed, if a large amount of n-type dopants is incorporated during the crystal growth of the active layer, crystal defects occur in the active layer, causing a decrease in luminance when current is applied.

[0016] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a compound semiconductor substrate having an AlGaInP quaternary light-emitting layer, which, when applied to a light-emitting device, can improve the luminance life characteristics when current is applied, and a method for manufacturing the compound semiconductor substrate. [Means for solving the problem]

[0017] In order to achieve the above object, the present invention provides a method for forming an n-type GaP substrate on which an Al x Ga 1-x ) y In 1-y P (where 0≦x≦1, 0≦y≦1), an active layer, and a p-type cladding layer are sequentially stacked, and a p-type GaP layer serving as a window layer is stacked on a second main surface of the quaternary light-emitting layer opposite to a first main surface on the n-type GaP substrate side. 15 (Atoms / cm 3 ) or less, n-type impurity concentration is 7 × 10 15 (Atoms / cm 3 The present invention provides a compound semiconductor substrate characterized in that:

[0018] This compound semiconductor substrate has GaP window layers (an n-type GaP substrate and a p-type GaP layer) on both sides (the first main surface and the second main surface) of the quaternary light-emitting layer, respectively, resulting in high external quantum efficiency and high brightness. Second, the active layer has low concentrations of both p-type and n-type impurities, suppressing both the diffusion of p-type dopants into the active layer and the generation of crystal defects in the active layer due to n-type dopants. As a result, when this compound semiconductor substrate is used in a light-emitting device, the amount of unnecessary dopant in the active layer is low, reducing the number of defects formed by the dopants when current is applied. This prevents defects from causing a decrease in carrier injection efficiency and an increase in light absorption, resulting in improved brightness life characteristics when current is applied.

[0019] Furthermore, it is preferable that the concentration of p-type impurities in the active layer is higher than the concentration of n-type impurities.

[0020] In this way, the concentration of p-type impurities, which diffuse more during current flow than n-type impurities, is sufficiently suppressed, and the concentration of n-type impurities is also lower than the concentration of p-type impurities, so that both the diffusion of p-type dopants into the active layer and the occurrence of crystal defects in the active layer due to n-type dopants can be reliably suppressed, thereby further improving the brightness life characteristics.

[0021] Preferably, the quaternary light-emitting layer has an undoped layer between the n-type cladding layer and the active layer, and the thickness of the undoped layer is 0.1 μm or more and 0.3 μm or less.

[0022] The presence of such a non-doped layer prevents direct contact between the n-type cladding layer and the active layer, i.e., prevents continuous crystal growth. This reduces the n-type dopant concentration in the crystal growth reactor before the active layer crystal growth, reducing the incorporation of n-type dopants into the active layer and suppressing the occurrence of crystal defects in the active layer. A non-doped layer thickness of 0.1 μm or more is preferable because it ensures good brightness life characteristics. Furthermore, a non-doped layer thickness of 0.3 μm or less is preferable because it barely causes any deterioration in electrical characteristics.

[0023] The present invention also provides a method for manufacturing a semiconductor device comprising: x Ga 1-x ) y In 1-y 1. A method for manufacturing a compound semiconductor substrate, comprising sequentially laminating at least an n-type cladding layer, an active layer, and a p-type cladding layer, each of which is made of P (where 0≦x≦1, 0≦y≦1), to form a quaternary light-emitting layer; laminating a p-type GaP layer serving as a window layer on the p-type cladding layer of the quaternary light-emitting layer; removing the substrate; and bonding an n-type GaP substrate or laminating an n-type GaP layer on the surface from which the substrate was removed, wherein the p-type impurity concentration in the active layer is 9×10 15 (Atoms / cm 3 ) below, the n-type impurity concentration is 7 × 10 15 (Atoms / cm 3 ) A method for manufacturing a compound semiconductor substrate is provided, which is characterized by:

[0024] This method of manufacturing a compound semiconductor substrate first forms GaP (a p-type GaP layer and an n-type GaP substrate or n-type GaP layer) on both sides of the quaternary light-emitting layer, thereby increasing the external quantum efficiency and achieving high brightness. Second, the concentrations of both the p-type and n-type impurities in the active layer are reduced, thereby suppressing both the diffusion of p-type dopants into the active layer and the generation of crystal defects in the active layer due to n-type dopants. As a result, when the manufactured compound semiconductor substrate is used in a light-emitting device, the amount of unnecessary dopant in the active layer is reduced, thereby reducing defects formed by the dopants when current is applied, preventing a decrease in carrier injection efficiency and an increase in light absorption due to defects, and improving the brightness life characteristics when current is applied.

[0025] Furthermore, it is preferable that the concentration of p-type impurities in the active layer is higher than the concentration of n-type impurities.

[0026] In this way, the concentration of p-type impurities, which diffuse more during current flow than n-type impurities, is sufficiently suppressed, and the concentration of n-type impurities is further made lower than the concentration of p-type impurities. This reliably suppresses both the diffusion of p-type dopants into the active layer and the occurrence of crystal defects in the active layer due to n-type dopants, thereby further improving the brightness life characteristics.

[0027] It is also preferable that an undoped layer is provided between the n-type cladding layer and the active layer of the quaternary light emitting layer, and the thickness of the undoped layer is set to 0.1 μm or more and 0.3 μm or less.

[0028] By including such a non-doped layer, the n-type cladding layer and the active layer are not in direct contact, i.e., they are not grown continuously. This reduces the n-type dopant concentration in the crystal growth reactor before the active layer crystal growth, reducing the incorporation of n-type dopants into the active layer and suppressing the occurrence of crystal defects in the active layer. A non-doped layer thickness of 0.1 μm or more is preferable because it ensures good brightness life characteristics. Furthermore, a non-doped layer thickness of 0.3 μm or less is preferable because it barely causes any deterioration in electrical characteristics. [Effects of the Invention]

[0029] The compound semiconductor substrate of the present invention has GaP window layers (an n-type GaP substrate and a p-type GaP layer) on both sides (a first main surface and a second main surface) of the quaternary light-emitting layer, respectively, thereby achieving high external quantum efficiency and high brightness. Second, the active layer has low concentrations of both p-type and n-type impurities, thereby suppressing both the diffusion of p-type dopants into the active layer and the generation of crystal defects in the active layer due to n-type dopants. As a result, when this compound semiconductor substrate is applied to a light-emitting device, the amount of unnecessary dopant in the active layer is reduced, thereby reducing the number of defects formed by the dopants when a current is applied. This prevents defects from causing a decrease in carrier injection efficiency and an increase in light absorption, thereby improving the lifetime characteristics of brightness when a current is applied.

[0030] Furthermore, the compound semiconductor substrate manufacturing method of the present invention first forms GaP (a p-type GaP layer and an n-type GaP substrate or n-type GaP layer) on both sides of the quaternary light-emitting layer, thereby increasing the external quantum efficiency and achieving high brightness. Second, the concentrations of both the p-type and n-type impurities in the active layer are reduced, thereby suppressing both the diffusion of p-type dopants into the active layer and the generation of crystal defects in the active layer due to n-type dopants. As a result, when the manufactured compound semiconductor substrate is applied to a light-emitting device, unnecessary dopants in the active layer can be reduced, thereby reducing defects formed by dopants during current application, preventing defects-related problems such as a decrease in carrier injection efficiency and an increase in light absorption, and improving the lifetime characteristics of brightness during current application. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a schematic diagram showing a compound semiconductor substrate according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a compound semiconductor substrate according to a second embodiment of the present invention. [Figure 3] FIG. 10 is a schematic diagram showing a compound semiconductor substrate according to a third embodiment of the present invention. [Figure 4]1 is a graph showing impurity concentrations in a compound semiconductor substrate. [Figure 5] 1A and 1B are diagrams illustrating wafer warpage and re-evaporation of n-type dopants during epitaxial growth. [Figure 6] 1 is a graph showing the correlation between luminance lifetime characteristics and impurity concentration. DETAILED DESCRIPTION OF THE INVENTION

[0032] As described above, there has been a demand for a compound semiconductor substrate and a method for manufacturing the compound semiconductor substrate that can improve the life characteristics of luminance when energized when applied to a light-emitting device.

[0033] In particular, in cases where the diffusion of p-type dopants into the active layer was sufficiently suppressed, but the luminance lifetime characteristics during life tests of light-emitting devices did not improve as expected, investigations revealed that the n-type dopant concentration in the active layer was high. In other words, when the diffusion of p-type dopants into the active layer was sufficiently suppressed, the impact of n-type dopants on luminance lifetime became apparent and was found to depend on the amount of n-type dopant in the active layer. Furthermore, in the case of n-type dopants, the amount of diffusion is not large, so it was found that the concentration of n-type dopants incorporated during the growth of the active layer directly affects the amount of defects that become non-emitting centers in the active layer, and methods for suppressing this were investigated.

[0034] After extensive investigations, the inventors have found that the luminance life characteristics when energized can be improved by providing GaP layers or GaP substrates on both sides of a quaternary light-emitting layer of a compound semiconductor substrate and by setting the p-type impurity concentration and the n-type impurity concentration in the active layer of the quaternary light-emitting layer to not more than predetermined values, respectively, and have completed the present invention.

[0035] That is, the present invention provides a method for forming an n-type GaP substrate on which an Al x Ga 1-x ) y In 1-yP (where 0≦x≦1, 0≦y≦1), an active layer, and a p-type cladding layer are sequentially stacked, and a p-type GaP layer serving as a window layer is stacked on a second main surface of the quaternary light-emitting layer opposite to a first main surface on the n-type GaP substrate side. 15 (Atoms / cm 3 ) or less, n-type impurity concentration is 7 × 10 15 (Atoms / cm 3 ) is a compound semiconductor substrate characterized in that:

[0036] The present invention also provides a method for manufacturing a semiconductor device comprising: x Ga 1-x ) y In 1-y 1. A method for manufacturing a compound semiconductor substrate, comprising sequentially laminating at least an n-type cladding layer, an active layer, and a p-type cladding layer, each of which is made of P (where 0≦x≦1, 0≦y≦1), to form a quaternary light-emitting layer; laminating a p-type GaP layer serving as a window layer on the p-type cladding layer of the quaternary light-emitting layer; removing the substrate; and bonding an n-type GaP substrate or laminating an n-type GaP layer on the surface from which the substrate was removed, wherein the p-type impurity concentration in the active layer is 9×10 15 (Atoms / cm 3 ) below, the n-type impurity concentration is 7 × 10 15 (Atoms / cm 3 ) is a method for manufacturing a compound semiconductor substrate, characterized in that:

[0037] The present invention will be described in detail below with reference to the drawings, but the present invention is not limited thereto.

[0038] [Compound semiconductor substrate] FIG. 1 is a schematic diagram showing a compound semiconductor substrate according to a first embodiment of the present invention.

[0039] On an n-type GaP substrate 11, (Al x Ga 1-x ) y In 1-yP (where 0≦x≦1, 0≦y≦1), an active layer 13, and a p-type cladding layer 14 are sequentially stacked on a quaternary light-emitting layer 15, and a p-type GaP layer 18 serving as a window layer is stacked on a second main surface 17 of the quaternary light-emitting layer 15 opposite to a first main surface 16 on the n-type GaP substrate 11 side. The p-type impurity concentration in the active layer 13 is 9×10 15 (Atoms / cm 3 ) or less, n-type impurity concentration is 7 × 10 15 (Atoms / cm 3 ) is as follows.

[0040] Such a compound semiconductor substrate 19 has GaP window layers (n-type GaP substrate 11 and p-type GaP layer 18) on both sides (first main surface 16 and second main surface 17) of quaternary light-emitting layer 15, respectively, thereby achieving high external quantum efficiency and high brightness. Second, the active layer 13 has low concentrations of both p-type and n-type impurities, thereby suppressing both the diffusion of p-type dopants contained in p-type cladding layer 14 into active layer 13 and the generation of crystal defects in active layer 13 due to n-type dopants contained in n-type cladding layer 12. As a result, when this compound semiconductor substrate 19 is used in a light-emitting device, the amount of unnecessary dopant in active layer 13 is low, thereby reducing the number of defects formed by the dopants during application of current. This prevents defects from causing a decrease in carrier injection efficiency and an increase in light absorption, thereby improving brightness lifetime characteristics during application of current.

[0041] Furthermore, although not particularly limited, the concentration of p-type impurities in the active layer 13 can be higher than the concentration of n-type impurities.

[0042] In this way, the p-type impurity concentration, which has a larger diffusion rate during current flow than the n-type, is sufficiently suppressed (9×10 15 (Atoms / cm 3 ) or less), and the n-type impurity concentration is (7 × 10 15 (Atoms / cm 3) and below) is lower than the p-type impurity concentration, it is possible to reliably suppress both the diffusion of p-type dopants into the active layer 13 and the occurrence of crystal defects in the active layer 13 due to n-type dopants, thereby further improving the brightness life characteristics.

[0043] 2 is a schematic diagram showing a compound semiconductor substrate according to a second embodiment of the present invention. The second embodiment differs from the first embodiment in that a non-doped layer (n-side) 20 is provided on the n-side of the quaternary light-emitting layer 15.

[0044] Although not particularly limited, the quaternary light-emitting layer 15 has an undoped layer (n-side) 20 between the n-type cladding layer 12 and the active layer 13, and although the thickness of the undoped layer (n-side) 20 is not particularly limited, it is preferably 0.1 μm or more and 0.3 μm or less.

[0045] The presence of this non-doped layer (n-side) 20 prevents direct contact between the n-type cladding layer 12 and the active layer 13, i.e., prevents continuous crystal growth. This reduces the n-type dopant concentration in the crystal growth reactor prior to crystal growth of the active layer 13, reducing the amount of n-type dopant taken up by the active layer 13 and suppressing the occurrence of crystal defects in the active layer 13. A thickness of the non-doped layer (n-side) 20 of 0.1 μm or more is preferable because it ensures good brightness life characteristics. Furthermore, a thickness of the non-doped layer (n-side) 20 of 0.3 μm or less is also preferable because it minimizes deterioration of electrical characteristics.

[0046] 3 is a schematic diagram showing a compound semiconductor substrate according to a third embodiment of the present invention. The third embodiment differs from the second embodiment in that the quaternary light-emitting layer 15 has an undoped layer (p-side) 21 on the p-side in addition to an undoped layer (n-side) 20 on the n-side.

[0047] Although not particularly limited, the quaternary light-emitting layer 15 has an undoped layer (p-side) 21 between the p-type cladding layer 14 and the active layer 13, and although the thickness of the undoped layer (p-side) 21 is not particularly limited, it is preferably 0.5 μm or more and 1.0 μm or less, and can be, for example, 0.8 μm.

[0048] The presence of such non-doped layer (p-side) 21 prevents direct contact between p-type cladding layer 14 and active layer 13, so that when p-type dopants in p-type cladding layer 14 diffuse, they diffuse from p-type cladding layer 14 to non-doped layer (p-side) 21, which further suppresses diffusion into active layer 13. A thickness of non-doped layer (p-side) 21 of 0.8 μm is preferable because it ensures good brightness life characteristics.

[0049] Here, a method for measuring the impurity concentration will be described. The impurity concentration is not particularly limited, but the average value in the active layer 13 can be calculated based on the analysis results of D-SIMS (Dynamic SIMS). For example, in a compound semiconductor substrate having a structure as shown in FIG. 3, if the substrate has a double heterostructure made of a quaternary mixed crystal of AlGaInP using, not particularly limited, Mg as a p-type dopant and, not particularly limited, Si as an n-type dopant, an example of a D-SIMS profile will be shown in FIG. 4.

[0050] The horizontal axis of the graph in Figure 4 shows the depth relative to the measurement surface, and the vertical axis shows the concentration of each impurity. If the measurement surface is the top surface of the substrate, the layer is determined by the depth, so from left to right on the graph it shows the change in concentration of each impurity (Mg, Si) in each layer: p-type cladding layer, non-doped layer (p-side), active layer, non-doped layer (n-side), and n-type cladding layer.

[0051] Referring to FIG. 4, first, the concentration of the p-type dopant Mg is naturally high in the p-type cladding layer (2×10 17 (Atoms / cm 3 )), but it drops sharply in the non-doped layer (p-side), and the concentration in the active layer is low (10 on average). 15 It can be seen that it is a platform.

[0052] Furthermore, the concentration of the n-type dopant Si is naturally high in the n-type cladding layer (7 × 10 17 However, it drops sharply in the non-doped layer (n-side) and the concentration is low in the active layer (10 on average). 15 It can be seen that it is a platform.

[0053] Therefore, if an undoped layer of an appropriate thickness, but not too thick, is provided between the cladding layer and the active layer, the impurity concentration in the undoped layer can be rapidly reduced, and as a result, the impurity concentration in the active layer can be adjusted to a desired low concentration.

[0054] [Method of manufacturing compound semiconductor substrate] A method for manufacturing a compound semiconductor substrate such as that shown in FIG. 1 will now be described.

[0055] (Step 1) First, a substrate is prepared.

[0056] (Step 2) Next, on the substrate, (Al x Ga 1-x ) y In 1-y A quaternary light-emitting layer 15 is formed by sequentially stacking at least an n-type cladding layer 12 made of P (where 0≦x≦1, 0≦y≦1), an active layer 13, and a p-type cladding layer 14.

[0057] (Step 3) Next, a p-type GaP layer 18 serving as a window layer is laminated on the p-type cladding layer 14 of the quaternary light-emitting layer 15 .

[0058] (Step 4) Next, the substrate is removed, and an n-type GaP substrate is bonded to the surface from which the substrate was removed (first main surface 16 in FIG. 1), or an n-type GaP layer is laminated thereon. In the example of FIG. 1, an n-type GaP substrate 11 is bonded.

[0059] The compound semiconductor substrate 19 manufactured by the above steps has a p-type impurity concentration of 9×10 15 (Atoms / cm 3 ) below, the n-type impurity concentration is 7 × 10 15 (Atoms / cm 3 ) or less.

[0060] In this way, in order to achieve a desired impurity concentration in the active layer 13 in the compound semiconductor substrate 19, although not particularly limited thereto, it is possible to appropriately adjust the dopant concentrations when stacking the n-type cladding layer 12 and the p-type cladding layer 14 in step 2, for example.

[0061] The substrate prepared in step 1 is not particularly limited, but may be a GaAs substrate.

[0062] This method of manufacturing the compound semiconductor substrate 19 first forms GaP (p-type GaP layer 18 and n-type GaP substrate 11 or n-type GaP layer) on both sides of the quaternary light-emitting layer 15, thereby increasing the external quantum efficiency and achieving high brightness. Second, the concentrations of both the p-type and n-type impurities in the active layer 13 are reduced, thereby suppressing both the diffusion of p-type dopants into the active layer 13 and the generation of crystal defects in the active layer 13 due to the n-type dopants. As a result, when the manufactured compound semiconductor substrate 19 is used in a light-emitting device, the amount of unnecessary dopant in the active layer 13 can be reduced, thereby reducing defects formed by the dopants when a current is applied. This prevents defects from causing a decrease in carrier injection efficiency and an increase in light absorption, resulting in improved brightness life characteristics when a current is applied.

[0063] Although not particularly limited, it is preferable that the concentration of p-type impurities in the active layer 13 be higher than the concentration of n-type impurities.

[0064] In this way, the concentration of p-type impurities, which diffuse more during current flow than n-type impurities, is sufficiently suppressed, and the concentration of n-type impurities is further made lower than the concentration of p-type impurities. This reliably suppresses both the diffusion of p-type dopants into the active layer 13 and the occurrence of crystal defects in the active layer 13 due to n-type dopants, thereby further improving the brightness life characteristics.

[0065] Furthermore, although not particularly limited, when manufacturing a compound semiconductor substrate such as that shown in FIGS. 2 and 3 above, an undoped layer (n-side) 20 is provided between the n-type cladding layer 12 and the active layer 13 of the quaternary light-emitting layer 15, and although there are no particular limitations on the thickness of the undoped layer (n-side) 20, it is preferable that the thickness be 0.1 μm or more and 0.3 μm or less.

[0066] By including such a non-doped layer (n-side) 20, the n-type cladding layer 12 and the active layer 13 are not in direct contact, i.e., the crystals are not grown continuously. This reduces the n-type dopant concentration in the crystal growth reactor before the crystal growth of the active layer 13, reducing the incorporation of n-type dopants into the active layer 13 and suppressing the occurrence of crystal defects in the active layer 13. Setting the thickness of the non-doped layer (n-side) 20 to 0.1 μm or more is preferable because it ensures good brightness life characteristics. Setting the thickness of the non-doped layer (n-side) 20 to 0.3 μm or less is also preferable because it hardly causes any deterioration in electrical characteristics.

[0067] In the above-described method for manufacturing a compound semiconductor substrate, the quaternary light-emitting layer 15 can be formed by MOVPE, although this is not particularly limited.

[0068] Here, when epitaxially growing (also called epi-growth) the active layer of the quaternary light-emitting layer by the MOVPE method, although not limited thereto, it is possible to suppress the incorporation of n-type impurities (n-type dopants) by controlling the amount of warping of the wafer during the reaction, as will be explained below with reference to FIG. 5.

[0069] For example, when a double heterostructure made of a quaternary mixed crystal of AlGaInP is epitaxially grown on a GaAs substrate, an n-type cladding layer, an active layer, and a p-type cladding layer are laminated in this order.

[0070] In epitaxial growth, a wafer 23 is set on a susceptor 22 in a reactor as shown in FIG. 5, and when the active layer is deposited, the supply of n-type dopant gas in the reactor is stopped. However, n-type dopant 25 is still present, having been re-evaporated from a precipitate 24 that had accumulated on the susceptor 22 up to that point.

[0071] Furthermore, during the reaction, the wafer 23 warps due to the difference in thermal expansion coefficient, becoming concave as shown in FIG. 5, and the temperature distribution within the surface of the wafer 23 changes accordingly.

[0072] In response to this, it is possible to suppress the incorporation of n-type impurities (n-type dopants) by appropriately changing the warpage of the wafer 23 to a desired shape by adjusting the growth temperature during epitaxial growth and the composition of the epitaxial layer to adjust the degree of lattice mismatch with the substrate (for example, by changing the In composition of AlGaInP).

[0073] The p-type impurity (dopant) concentration in the active layer is set to 9 × 10 15 (Atoms / cm 3 ) or less, the n-type impurity (dopant) concentration is 7 × 10 15 (Atoms / cm 3 ) or less, it is possible to sufficiently suppress the conventional problem of reduced brightness due to p-type dopant diffusion, and further improve the brightness life characteristics. This will be explained in detail with reference to FIG.

[0074] FIG. 6 is a graph showing the correlation between the luminance lifetime characteristics and the impurity concentration in a lifetime test, in which Mg is used as a p-type dopant and Si is used as an n-type dopant.

[0075] From Figure 6, the p-type impurity concentration is 9×10 15 (Atoms / cm 3 ) or less, there is almost no correlation between the p-type impurity concentration and the luminance lifetime characteristics. On the other hand, when the n-type impurity concentration is 3×10 15 ~2×10 16 (Atoms / cm 3 ) range, a good correlation is obtained.

[0076] In reality, the p-type impurity concentration and n-type impurity concentration are determined individually for each product, so the p-type impurity concentration is 9 × 10 15(Atoms / cm 3 ) or less, the lifetime characteristics are determined by the n-type impurity concentration. If the p-type impurity concentration is 9 × 10 15 (Atoms / cm 3 ) or less, and the n-type impurity concentration is 7 × 10 15 (Atoms / cm 3 ), the brightness lifespan is 88% or more.

[0077] Furthermore, the n-type impurity concentration is increased to 3×10 15 (Atoms / cm 3 ), it can be seen from Figure 6 that the luminance life characteristics can be improved to 94%.

[0078] In general, compared to p-type dopants, n-type dopants are subject to extremely small impurity diffusion due to thermal history and current flow, and it has been thought that their impact on luminance life characteristics is minimal.

[0079] On the other hand, if a large amount of n-type impurities (dopants) is incorporated into the active layer during epitaxial growth using the MOVPE method, crystal defects increase, and in life tests, rapid deterioration can occur, with brightness dropping to about half of its initial value within about 100 hours (this will be explained later in Comparative Example 2).

[0080] Since p-type dopants diffuse more easily into the active layer than n-type dopants, the carrier concentration of the p-type cladding layer is generally set lower than that of the n-type cladding layer.

[0081] On the other hand, as mentioned above, in order to achieve a longer brightness lifespan, it is preferable to suppress impurities in the active layer, i.e., p-type dopants, and furthermore make the n-type impurity concentration lower than the p-type impurity concentration, which has been shown to be able to sufficiently suppress the effects of the fast degradation mode. [Example]

[0082] Example 1 <Fabrication of Compound Semiconductor Substrates> A compound semiconductor substrate was fabricated as shown in Figure 3. First, epitaxial growth was carried out by MOVPE according to the following steps (1) to (8).

[0083] (1) A 2-inch (50 mm) diameter, 280 μm thick n-type GaAs substrate (15° off-angle, Si-doped) was grown on a Si-doped n-GaAs buffer layer (0.5 μm, 5.0 × 10 17 Atoms / cm 3 ) was grown.

[0084] (2) On top of that, as an n-type cladding layer, Si-doped n-AlGaInP (1.3 μm, 1.0 × 10 18 Atoms / cm 3 ) was grown.

[0085] (3) On top of this, non-doped i-AlGaInP (0.2 μm) was grown.

[0086] (4) On top of that, we grew 9 pairs of non-doped i-AlGaInP (0.02 μm, well layer) and non-doped i-AlGaInP (0.02 μm, barrier layer) + non-doped i-AlGaInP (0.02 μm, well layer) as the active layer.

[0087] (5) On top of this, non-doped i-AlGaInP (0.8 μm) was grown.

[0088] (6) On top of that, as a p-type cladding layer, Mg-doped p-AlGaInP (1.8 μm, 2.0 × 10 17 Atoms / cm 3 ) was grown.

[0089] (7) On top of that, a Mg-doped p-type GaP layer (1.6 μm, 2.0 × 10 17 Atoms / cm 3 to 2.0 x 10 18 Atoms / cm 3 This has led to the growth of the

[0090] (8) The source gases used were TMAl, TMGa, TMIn, AsH3, PH3, SiH4, and Cp2Mg. The furnace pressure was reduced to 100 hPa or less, and the growth temperature was 690°C.

[0091] (9) Next, a Zn-doped p-type GaP layer (60 μm, 8.0 × 10 17 Atoms / cm 3 ) was grown.

[0092] (10) Next, the GaAs substrate and the n-GaAs buffer layer were removed, and an n-type GaP substrate was bonded to the GaAs substrate. This completed the compound semiconductor substrate of Example 1.

[0093] <Fabrication of light-emitting element> Next, a first (p) electrode and a second (n) electrode were formed on the compound semiconductor substrate by vacuum deposition, and a bonding pad was placed on the first electrode and baked at an appropriate temperature to fix the electrodes. After that, the substrate was diced into chips, and the second electrode was fixed to a terminal electrode that also served as a support using a conductive paste such as an Ag base. Au wire was bonded across the bonding pad and another terminal electrode, and a resin mold was then formed to fabricate a light-emitting element.

[0094] <Evaluation method for light-emitting elements> In order to evaluate the characteristics of the fabricated light-emitting device, the following evaluations were carried out.

[0095] First, to evaluate the initial brightness, the omnidirectional light output when a DC current of 20 mA was applied was measured using an integrating sphere. Then, to evaluate the lifespan characteristics, the brightness was evaluated after 100 hours in an accelerated test with a DC current of 50 mA and an ambient temperature of 85°C, and the deterioration of the initial brightness was evaluated.

[0096] Before the accelerated test, the light emitting device was subjected to D-SIMS measurement to evaluate the impurity concentration in the active layer.

[0097] (Comparative Example 1) The fabrication and evaluation were carried out in the same manner as in Example 1, except that the thickness of the non-doped (n-side) i-AlGaInP in (3) above was set to 0.1 μm.

[0098] (Comparative Example 2) The fabrication and evaluation were carried out in the same manner as in Example 1, except that the thickness of the non-doped (n-side) i-AlGaInP in (3) above was set to 0 μm (none).

[0099] (Comparative Example 3) As the p-type cladding layer of the above (6), Mg-doped p-AlGaInP (1.8 μm, 3.0 × 10 17 Atoms / cm 3 ) was used, the preparation and evaluation were carried out in the same manner as in Example 1.

[0100] Example 2 The fabrication and evaluation were carried out in the same manner as in Example 1, except that the thickness of the non-doped (n-side) i-AlGaInP in (3) above was 0.1 μm and the growth temperature in (8) above was 700° C.

[0101] Comparative Example 4 The fabrication and evaluation were carried out in the same manner as in Example 1, except that the thickness of the non-doped (n-side) i-AlGaInP in (3) above was 0.1 μm and the growth temperature in (8) above was 710° C.

[0102] <Evaluation results> First, Table 1 shows the brightness lifetime characteristics and impurity concentration in the active layer for Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 when the thickness of the non-doped (n-side) i-AlGaInP (3) above and the carrier concentration of the p-type cladding layer (6) above are changed.

[0103] [Table 1]

[0104] First, in Example 1, the p-type impurity concentration is 9×10 15 (Atoms / cm 3 ) or less, n-type impurity concentration is 7 × 1015 (Atoms / cm 3 ) or less, and the brightness life characteristics were 92.9%, which was an extremely good result.

[0105] Next, in Comparative Example 1 and Comparative Example 2, the p-type impurity concentration was 9×10 15 (Atoms / cm 3 ) or less, but the n-type impurity concentration is 7 × 10 15 (Atoms / cm 3 ) and the brightness life characteristics were worse at 88.9% and 48.6%.

[0106] Next, in Comparative Example 3, the p-type impurity concentration was 9×10 15 (Atoms / cm 3 ) and the n-type impurity concentration is 7×10 15 (Atoms / cm 3 ) or less, the brightness life characteristics were poor at 86.8%.

[0107] Comparing Comparative Example 1 and Example 1, the thickness of the non-doped layer (n-side) is 0.1 μm in Comparative Example 1 and 0.2 μm in Example 1. By increasing the thickness of the non-doped layer (n-side), the impurity (Si, which is an n-type dopant) concentration in the active layer is reduced to 7×10 15 (Atoms / cm 3 ) or less, which is thought to have resulted in a favorable result of brightness life characteristics of 90% or more.

[0108] In Comparative Example 2, the non-doped layer (n-side) was omitted, and the brightness lifespan characteristics were significantly worsened. The absence of the non-doped layer (n-side) led to the incorporation of a large amount of n-type impurities (dopants) into the active layer, which is thought to have increased crystal defects and caused rapid deterioration in the lifespan test, with brightness dropping to about half of its initial value.

[0109] Furthermore, in Comparative Example 3, the carrier concentration of p-AlGaInP was 3.0×10 17 (Atoms / cm 3), that is, the concentration of Mg, a p-type impurity in the active layer, was intentionally increased, and the p-type impurity concentration was 9 × 10 15 (Atoms / cm 3 ) and therefore the luminance life characteristics are thought to have deteriorated.

[0110] Here, we will further consider the effect of the thickness of the non-doped layer (n-side). If the non-doped layer (n-side) is made thicker, the resistance value of the light-emitting device increases, and the forward voltage increases (deteriorates). If the non-doped layer (n-side) is made thicker, the Si concentration in the active layer decreases, but the increase in forward voltage becomes non-negligible. Therefore, it is not possible to make it thicker without limit.

[0111] Table 2 shows the luminance lifetime characteristics and the forward voltage (normalized to Example 1 as 1.00) when a forward current of 20 mA is applied when the thickness of the non-doped layer (n-side) is changed.

[0112] [Table 2]

[0113] When the thickness of the non-doped layer (n-side) is in the range of 0.06 to 0.3 μm, the forward voltage is equivalent, but at a thickness of 0.6 μm, it increases by 1% or more.

[0114] Therefore, although there are no particular limitations, the thickness of the non-doped layer (n-side) is preferably 0.3 μm or less in order to suppress the effect on the forward voltage.

[0115] Although not particularly limited, the thickness of the non-doped layer (n-side) is preferably 0.1 μm or more in order to avoid deterioration of the luminance life characteristics.

[0116] Next, Table 3 shows the brightness lifetime characteristics and impurity concentration in the active layer for Example 2, Comparative Example 1, and Comparative Example 4 when the thickness of the non-doped layer (n-side) is fixed at 0.1 μm and the growth temperature is changed.

[0117] [Table 3]

[0118] First, in Example 2, the p-type impurity concentration is 9×10 15 (Atoms / cm 3 ) or less, n-type impurity concentration is 7 × 10 15 (Atoms / cm 3 ) or less, and the brightness life characteristics were 91.9%, which was an extremely good result.

[0119] Next, in Comparative Example 1 and Comparative Example 4, the p-type impurity concentration was 9×10 15 (Atoms / cm 3 ) or less, but the n-type impurity concentration is 7 × 10 15 (Atoms / cm 3 ) and the brightness life characteristics were worse at 88.9% and 79.5%.

[0120] The growth temperature was set to 700°C in Example 2 and 690°C in Comparative Example 1. When the growth temperature is lowered in this way, the wafer warpage (concave shape) during the reaction increases, and the wafer temperature decreases, which reduces the amount of n-type dopant re-evaporated from the wafer and increases the concentration of impurities (Si, which is an n-type dopant) in the active layer, which increases the occurrence of crystal defects due to the impurities, presumably resulting in a deterioration in life characteristics.

[0121] Furthermore, the growth temperature was 710°C in Comparative Example 4, compared to 700°C in Example 2. When the growth temperature is increased in this way, wafer warpage (concave shape) during the reaction is reduced and the wafer temperature does not decrease, but the amount of re-evaporation of n-type dopant from precipitates in the furnace increases, increasing the incorporation of impurities (Si as n-type dopant), and presumably deteriorating the life characteristics.

[0122] In summary, in Examples 1 and 2, the p-type impurity concentration in the active layer is 9×10 15 (Atoms / cm 3 ) or less, n-type impurity concentration is 7 × 1015 (Atoms / cm 3 ) or less, which indicates that the luminance life characteristics are good.

[0123] Furthermore, comparing Example 1 and Example 2 with reference to Tables 1 and 3, it was found that Example 1, in which the p-type impurity concentration in the active layer was higher than the n-type impurity concentration, had better brightness life characteristics. This means that when the p-type impurity concentration was sufficiently suppressed, the n-type impurity concentration was lower than the p-type impurity concentration, and it is believed that this reliably suppresses both the diffusion of p-type dopants into the active layer and the occurrence of crystal defects in the active layer due to n-type dopants, thereby further improving brightness life characteristics.

[0124] Furthermore, both Examples 1 and 2 have an undoped layer between the n-type cladding layer and the active layer, and the thickness of this undoped layer is in the range of 0.1 μm to 0.3 μm. The evaluation results of Examples 1 and 2 showed that in addition to having good luminance life characteristics, there was almost no deterioration in electrical characteristics, which was more preferable.

[0125] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0126] 11...n-type GaP substrate (window layer), 12...n-type cladding layer, 13...active layer, 14...p-type cladding layer, 15...quaternary light-emitting layer, 16...first main surface, 17... second main surface, 18... p-type GaP layer (window layer), 19... compound semiconductor substrate, 20... Non-doped layer (n-side), 21... Non-doped layer (p-side), 22... Susceptor, 23...wafer, 24...precipitate, 25...re-evaporated n-type dopant.

Claims

1. On an n-type GaP substrate, (Al ｘ Ga １－ｘ ) ｙ In １－ｙ P (where 0≦x≦1, 0≦y≦1), an n-type clad layer, an active layer, and a p-type clad layer are sequentially stacked, a compound semiconductor substrate in which a p-type GaP layer serving as a window layer is stacked on a second main surface of the quaternary light-emitting layer opposite to a first main surface on the n-type GaP substrate side, The p-type impurity concentration in the active layer is 9×10 １５ (Atoms / cm ３ ) or less, the n-type impurity concentration is 7×10 １５ (Atoms / cm ３ ) or less.

2. 2. The compound semiconductor substrate according to claim 1, wherein the concentration of p-type impurities in the active layer is higher than the concentration of n-type impurities.

3. 3. The compound semiconductor substrate according to claim 1, wherein the quaternary light-emitting layer has an undoped layer between the n-type cladding layer and the active layer, and the thickness of the undoped layer is 0.1 μm or more and 0.3 μm or less.

4. On the substrate, (Al ｘ Ga １－ｘ ) ｙ In １－ｙ a quaternary light-emitting layer is formed by sequentially stacking at least an n-type cladding layer, an active layer, and a p-type cladding layer made of P (where 0≦x≦1, 0≦y≦1); a p-type GaP layer serving as a window layer is laminated on the p-type cladding layer of the quaternary light-emitting layer; A method for manufacturing a compound semiconductor substrate, comprising removing the substrate, and bonding an n-type GaP substrate or laminating an n-type GaP layer on a surface from which the substrate was removed, The p-type impurity concentration in the active layer is 9×10 １５ (Atoms / cm ３ ) Hereinafter, the n-type impurity concentration is set to 7×10 １５ (Atoms / cm ３ 1. A method for manufacturing a compound semiconductor substrate, comprising:

5. 5. The method for manufacturing a compound semiconductor substrate according to claim 4, wherein the concentration of p-type impurities in the active layer is higher than the concentration of n-type impurities.

6. 6. The method for manufacturing a compound semiconductor substrate according to claim 4, wherein a non-doped layer is provided between the n-type cladding layer and the active layer of the quaternary light-emitting layer, and the thickness of the non-doped layer is set to 0.1 μm or more and 0.3 μm or less.

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