JP3967088B2 - Semiconductor light emitting device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light-emitting device, and more particularly to a semiconductor light-emitting device that is suitable for light emission in a wavelength region where the light receiving sensitivity of a photodiode using silicon is high and can suppress a decrease in light output.
[0002]
[Prior art]
As a device that outputs light in an infrared wavelength region (infrared region having a wavelength of 920 nm or less) with a high light receiving sensitivity of a photodiode using silicon, a double hetero-type light emitting diode in which a Zn-doped GaAs layer is sandwiched between AlGaAs layers is used. Are known. This double heterostructure is usually formed on a GaAs substrate. The light emitted from the GaAs light emitting layer is absorbed by the GaAs substrate. Therefore, light cannot be extracted to the substrate side.
[0003]
A technique is known in which an n-type AlGaAs cladding layer, a p-type GaAs active layer, and a p-type AlGaAs cladding layer are formed on a GaAs substrate by liquid phase epitaxy, and then the GaAs substrate is removed by mechanical polishing or the like. (Refer to the prior art of JP-A-63-312585). However, with this method, it is difficult to obtain a light-emitting element that can operate at high speed at high efficiency.
[0004]
Japanese Patent Application Laid-Open No. 63-312585 discloses a technique for forming an AlGaAs cladding layer and an AlGaAs or GaAs active layer on an AlGaAs substrate by metal organic chemical vapor deposition (MOCVD). However, it only describes that an AlGaAs substrate is prepared, and does not describe any method for manufacturing the AlGaAs substrate.
[0005]
[Problems to be solved by the invention]
When the inventors of the present invention fabricated a semiconductor light emitting device by epitaxially growing a semiconductor layer on an AlGaAs substrate, it was found that a sufficient lifetime could not be obtained.
[0006]
An object of the present invention is to provide a semiconductor light emitting device that has a longer life than conventional ones.
[0009]
[Means for Solving the Problems]
According to an aspect of the present invention, a support substrate made of a semiconductor material, and a buffer layer including a layer disposed on the support substrate and formed of a semiconductor material having a lattice constant larger than the lattice constant of the support substrate; A lower carrier confinement layer disposed on the buffer layer and formed of a semiconductor material; and a semiconductor material formed on the lower carrier confinement layer and having a smaller band gap than the lower carrier confinement layer. an active layer formed, is formed on the active layer, have a upper carrier confinement layer formed of a semiconductor material having a larger band gap than the active layer, the supporting substrate, a lower carrier confinement layer, and upper carrier confinement layer comprises Al and Ga as group III elements, formed of a compound semiconductor material containing as as group V element, wherein the buffer layer is an in _1-x Al _z Ga _1-z) comprises a layer formed by x As (0 <x <1 , and 0 ≦ z ≦ 1), said active layer comprises In and Ga as group III elements, group V elements A semiconductor light emitting device formed of a compound semiconductor material containing As is provided.
[0010]
By disposing the above buffer layer between the support substrate and the lower carrier confinement layer, the propagation of crystal defects in the support substrate is suppressed, and a carrier confinement layer and an active layer with good crystallinity are formed. Can do.
[0013]
According to another aspect of the present invention, a step of liquid phase epitaxial growth of a support layer made of a semiconductor material different from the temporary substrate on the surface of the temporary substrate made of a semiconductor material, removing the temporary substrate, and supporting the support Leaving a support substrate made of a layer, growing a buffer layer including a layer made of a semiconductor material having a lattice constant larger than the lattice constant of the support substrate on the surface of the support substrate; and above, the active layer, and sandwich the active layer than the active layer have a forming a light emitting structure including a large pair of carrier confinement layer of the band gap, the temporary substrate is formed by GaAs, the support layer and carrier confinement layer comprises Al and Ga as group III elements, formed of a compound semiconductor material containing as as group V element, wherein the buffer layer _{is an in 1-x} (Al Ga _1-z) comprises a layer formed by x As (0 <x <1 , and 0 ≦ z ≦ 1), said active layer comprises In and Ga as group III elements, As as group V element A method for manufacturing a semiconductor light emitting device formed of a compound semiconductor material is provided.
[0014]
By disposing the above buffer layer between the support substrate and the lower carrier confinement layer, the propagation of crystal defects in the support substrate is suppressed, and a carrier confinement layer and an active layer with good crystallinity are formed. Can do.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a sectional view of a semiconductor light emitting device according to an embodiment of the present invention. The support substrate 4 is composed of two layers of the high concentration layer 2 and the low concentration layer 3. The support substrate 4 is formed of p-type Al _0.26 Ga _0.74 As doped with Zn. The high concentration layer 2 has a Zn concentration of 1 × 10 ¹⁸ cm ⁻³ , and the low concentration layer 3 has a Zn concentration of 5 × 10 ¹⁷ cm ⁻³ . The high concentration layer 2 has a thickness of 40 μm, and the low concentration layer 3 has a thickness of 110 μm.
[0016]
Each layer from the AlGaAs buffer layer 5 to the GaAs contact layer 12 is formed on the surface of the low concentration layer 3 by metal organic chemical vapor deposition (MOCVD). The buffer layer 5 is made of Zn-doped p-type Al _0.26 Ga _0.74 As, and has a thickness of 2 μm and a Zn concentration of 1 × 10 ¹⁸ cm ⁻³ .
[0017]
The lower cladding layer 6 is formed of p-type Al _0.32 Ga _0.68 As doped with Zn, has a thickness of 1.0 μm, and a Zn concentration of 1 × 10 ¹⁸ cm ⁻³ . The lower carrier confinement layer (CCL layer) 7 is formed of Al _0.18 Ga _0.82 As not intentionally doped with impurities, and has a thickness of 2 to 190 nm, more preferably 10 to 50 nm. The background concentration of Zn in the lower CCL layer 7 is 5 × 10 ¹⁶ to 1 × 10 ¹⁷ cm ⁻³ .
[0018]
The strain quantum well layer (active layer) 8 is made of InGaAs, and has a thickness of 2.4 to 15 nm and an In composition ratio of 0.12 to 0.25. The upper carrier confinement layer 9 is made of Al _0.18 Ga _0.82 As not intentionally doped with impurities, and has a thickness of 2 to 190 nm, more preferably 10 to 50 nm. The Si background concentration of the upper carrier confinement layer 9 is 5 × 10 ¹⁶ to 1 × 10 ¹⁷ cm ⁻³ . The upper cladding layer 10 is made of Si-doped n-type Al _0.32 Ga _0.68 As, has a thickness of 5.5 μm, and a Si concentration of 1 × 10 ¹⁸ cm ⁻³ .
[0019]
The current spreading layer 11 is formed of n-type Al _0.18 Ga _0.82 As doped with Si, has a thickness of 4.5 μm, and has a Si concentration of 1 × 10 ¹⁸ cm ⁻³ . The contact layer 12 is made of n-type GaAs doped with Si, and has a thickness of 0.1 μm and a Si concentration of 2 × 10 ¹⁸ cm ⁻³ .
[0020]
On the contact layer 12, an n-side electrode 15 in which a Ni layer, a Ge layer, and an Au layer are stacked in order from the bottom is formed. The n-side electrode 15 has, for example, an X-shaped planar shape by a lift-off method. A p-side electrode 16 in which an Au layer and an AuZn alloy layer are sequentially stacked from the support substrate 4 side is formed on the surface of the high concentration layer 2 constituting a part of the support substrate 4. The p-side electrode 16 is formed in, for example, a honeycomb shape by a lift-off method.
[0021]
Next, with reference to FIG. 2, a method of manufacturing the base substrate 4 used in the semiconductor light emitting device according to the above embodiment will be described.
[0022]
A temporary substrate 1 made of GaAs shown in FIG. The main surface of the temporary substrate 1 is a (100) surface of GaAs. The temporary substrate 1 is doped with Zn to give p-type conductivity, and its concentration is 2 to 5 × 10 ¹⁹ cm ⁻³ .
[0023]
On the main surface of the temporary substrate 1, a high-concentration layer 2 having a thickness of 40 μm and a low-concentration layer 3 having a thickness of 150 μm made of Al _0.26 Ga _0.74 As are sequentially grown by liquid phase epitaxial growth (LPE). These two layers become the support substrate 4. LPE mainly includes a temperature difference method and a slow cooling method, but here, a temperature difference method is adopted. By adopting the temperature difference method, the Al composition ratio of the support substrate 4 can be made substantially uniform. As the growth apparatus, for example, a slide boat type can be used. The high-concentration layer 2 and the low-concentration layer 3 are doped with Zn during growth so that the Zn concentrations are 1 × 10 ¹⁸ cm ⁻³ and 5 × 10 ¹⁷ cm ⁻³ , respectively.
[0024]
The growth solution used is a solution in which GaAs, Al and Zn are dissolved in a Ga solvent. The temperature gradient in the vertical direction of the growth solution filled in the melt tank is about 5 ° C./cm, and the temperature at the bottom of the growth solution in contact with the seed crystal is about 830 to 850 ° C. Note that the temperature and temperature gradient in the lower portion of the growth solution are kept substantially constant during the growth.
[0025]
Processes up to the state shown in FIG. The temporary GaAs substrate 1 shown in FIG. 1 is removed by etching. As a result, only the support substrate 4 remains. The temporary substrate 1 made of GaAs can be etched using an etching solution in which ammonia water and hydrogen peroxide water are mixed at a volume ratio of 20: 1. The concentration of ammonia water is 28% by weight, and the concentration of hydrogen peroxide water is 31% by weight.
[0026]
Next, the surface of the low concentration layer 3 is ground to reduce unevenness. Further, the ground surface is polished to remove processing damage, and then final finishing is performed by chemical mechanical polishing (CMP). In general, a semiconductor layer grown by a temperature difference method has poor surface flatness compared to a semiconductor grown by a slow cooling method. By performing the final finishing by CMP, the flatness of the surface can be improved. The support substrate 4 is obtained through the steps so far.
[0027]
By applying a forward bias between the n-side electrode 15 and the p-side electrode 16 and injecting carriers into the strained quantum well layer 8, light emission in the infrared region (wavelength 800 to 920 nm) can be generated. .
[0028]
In the above embodiment, the support substrate 4 made of AlGaAs serves as a substrate having physical support force and also serves as a seed crystal for MOCVD. Since GaAs is not used as the substrate material, light can be extracted not only from the contact layer 12 side shown in FIG. 1 but also from the support substrate 4 side. Since the contact layer 12 made of GaAs is very thin, it is removed by acid treatment in a later chip forming process. For this reason, it does not become an obstacle of light extraction. The effect of removing the temporary substrate 1 is particularly high when the wavelength giving the peak of the emission spectrum of the strained quantum well layer 8 is shorter than the wavelength corresponding to the band gap of the semiconductor material forming the temporary substrate 1.
[0029]
The lower carrier confinement layer 7, the strained quantum well layer 8, and the upper carrier confinement layer 9 are formed by MOCVD. For this reason, compared with the case where these layers are formed by LPE, the uniformity of the film thickness can be increased, and high luminous efficiency can be realized. Note that molecular beam epitaxial growth (MBE) may be used instead of MOCVD.
[0030]
FIG. 3 shows secondary ion mass spectrometry (SIMS) results of the impurity concentration in the depth direction in the vicinity of the interface between the support substrate and the buffer layer manufactured by the same method as the semiconductor light emitting device shown in FIG. The horizontal axis represents the position in the depth direction in the unit “μm”, the left vertical axis represents the concentration of carbon atoms and oxygen atoms in the unit “atom / cm ³ ”, and the right vertical axis represents the secondary ion of Al. Intensity is expressed in units of “counts / second”. The semiconductor light emitting device according to the embodiment shown in FIG. 1 and the sample to be measured shown in FIG. 3 have different Al composition ratios.
[0031]
A fall in the secondary ion intensity of Al is observed at a depth of 1.38 μm. This position corresponds to the interface between the AlGaAs support layer and the Al _0.26 Ga _0.74 As layer grown thereon by MOCVD. A peak of oxygen concentration appears at the interface between the support layer and the Al _0.26 Ga _0.74 As layer.
[0032]
In the case of the semiconductor light emitting device of FIG. 1, since the Al composition ratio of the support substrate 4 and the buffer layer 5 is the same, a step in the secondary ion intensity of Al does not appear at a position corresponding to the interface. The peak of oxygen concentration appears. By detecting this peak of oxygen concentration, the interface between the support substrate 4 and the buffer layer 5 can be specified.
[0033]
Next, various modifications of the buffer layer 5 shown in FIG. 1 will be described with reference to FIGS.
[0034]
The buffer layer 5A shown in FIG. 4A is formed of p-type Al _0.26 a _0.74 As doped with Zn by 1 × 10 ¹⁸ cm ⁻³ , and its thickness is 1 μm, and is shown in FIG. The buffer layer 5 has the same structure. The buffer layer shown in FIG. 4B is composed of a p-type In _0.005 (Al _0.26 Ga _0.74 ) _0.995 As layer 5B having a thickness of 1 μm. The Zn concentration of the buffer layer 5B is 1 × 10 ¹⁸ cm ⁻³ . Hereinafter, the buffer layer of FIGS. 4C to 5G is similarly doped with Zn by 1 × 10 ¹⁸ cm ⁻³ .
[0035]
The buffer layer shown in FIG. 4C is composed of an In _0.01 (Al _0.26 Ga _0.74 ) _0.99 As layer having a thickness of 1 μm. The buffer layer shown in FIG. 4D is composed of an Al _0.26 Ga _0.74 As layer 5Da having a thickness of 0.2 μm, an In _0.12 Ga _0.88 As layer 5Db having a thickness of 5 nm, and an Al layer having a thickness of 5 nm in this order from the support substrate 4 side. It has a three-layer structure in which a _0.26 Ga _0.74 As layer 5Dc is laminated.
[0036]
In the buffer layer 5 shown in FIG. 4E, an Al _0.26 Ga _0.74 As layer 5Ea having a thickness of 0.2 μm is disposed closest to the support substrate 4 side. A quantum well structure in which an In _0.12 Ga _0.88 As layer 5Eb having a thickness of 5 nm and an Al _0.26 Ga _0.74 As layer 5Ec having a thickness of 5 nm are alternately stacked is disposed thereon. Three InGaAs layers 5Eb are arranged, and two AlGaAs layers 5Ec are arranged.
[0037]
In the buffer layer 5 shown in FIG. 5F, an Al _0.26 Ga _0.74 As layer 5Fa having a thickness of 0.2 μm is disposed closest to the support substrate 4 side. A quantum well structure in which an In _0.12 Ga _0.88 As layer 5Fb having a thickness of 5 nm and an Al _0.26 Ga _0.74 As layer 5Fc having a thickness of 5 nm are alternately stacked is disposed thereon. Five InGaAs layers 5Fb are arranged, and four AlGaAs layers 5Fc are arranged.
[0038]
In the buffer layer 5 shown in FIG. 5G, an Al _0.26 Ga _0.74 As layer 5Ga having a thickness of 0.2 μm is disposed closest to the support substrate 4 side. On top of this, 5 nm thick In _0.12 Ga _0.88 As layers 5 Gb and 5 nm thick Al _0.26 Ga _0.74 As layers 5 Gc are alternately stacked. Five InGaAs layers 5Gb are arranged, and four AlGaAs layers 5Gc are arranged.
[0039]
On top of this, an Al _0.26 Ga _0.74 As layer 5Gd having a thickness of 0.2 μm is disposed. Furthermore, an In _0.12 Ga _0.88 As layer 5Ge having a thickness of 5 nm and an Al _0.26 Ga _0.74 As layer 5Gf having a thickness of 5 nm are alternately stacked thereon. Five InGaAs layers 5Ge are arranged, and four AlGaAs layers 5Gf are arranged.
[0040]
The samples having the structure shown in FIGS. 4A to 5G are referred to as samples A to G, respectively.
[0041]
FIG. 6 shows the relationship between the energization time of samples A to G and the normalized light output. The horizontal axis represents the energization time in the unit “time”, and the vertical axis represents the normalized light output. The normalized light output is a relative value where the initial value of the light output of each sample is 100. Curves A to G in the figure show the normalized light outputs of samples A to G, respectively. For comparison, the thickness of the AlGaAs layer 5A in FIG. 4A is 0.2 μm (the distance from the interface between the support substrate and the buffer layer to the lower surface of the active layer is 0.2 μm + 1.0 μm + 2 to 190 nm). The normalized light output of the semiconductor light emitting device (comparative example) is shown by a curve R. The bias current is 100 mA, and each sample has a square shape with one side of 370 μm × 370 μm.
[0042]
The light output of the comparative example decreases significantly as the energization time increases. Observation of the sample after energization for a long time revealed that there was a dark spot that did not emit light in the light output surface. It is considered that the support substrate 4 manufactured by LPE has poor crystallinity, and dark spots are generated in a portion with many crystal defects.
[0043]
In Sample A, a decrease in light output is suppressed as compared with the comparative example. This is because part of the crystal defects in the support substrate 4 does not propagate to the upper surface of the buffer layer 5A by increasing the thickness of the buffer layer 5A formed by MOCVD, and the crystal above the lower cladding layer 6 is crystallized. This is thought to be because of improved sex. Thus, by forming a buffer layer made of the same semiconductor material as that of the support substrate 4 to 2 μm or more, it is possible to suppress a decrease in light output. The same effect is expected even when the distance from the interface between the support substrate 4 and the buffer layer 5A to the lower surface of the active layer (strained quantum well layer 8) is 2 μm or more.
[0044]
By adopting the structures of Samples B and C, it can be seen that the decrease in light output can be suppressed as shown by curves B and C. This is presumably because the propagation of crystal defects was suppressed and the crystallinity was improved by adding In to the buffer layer.
[0045]
It can be seen that even if the structures of the samples D to G are employed, a decrease in light output can be suppressed as shown by the curves D to G. This is presumably because the propagation of crystal defects was suppressed and the crystallinity was improved by inserting an InGaAs layer in the buffer layer 5. The thickness of the InGaAs layer needs to be equal to or less than the maximum film thickness (critical film thickness) capable of absorbing the difference in lattice constant and epitaxially growing. The InGaAs layer may be a single layer as shown in FIG. 4D or a plurality of layers as shown in FIGS. 4E to 5G.
[0046]
The lattice constant of InAlGaAs or InGaAs is larger than the lattice constant of AlGaAs. Thus, by inserting a buffer layer made of a semiconductor material having a lattice constant larger than the lattice constant of the support substrate between the support substrate and the lower cladding layer, the crystallinity of the semiconductor layer grown thereon And lowering of the light output can be suppressed. The lower cladding layer, the lower carrier confinement layer, the upper carrier confinement layer, and the upper clad layer are substantially lattice-matched to the support substrate.
[0047]
The band gap of the buffer layer inserted between the support substrate and the lower clad layer is different from the band gap of the support substrate or the lower clad layer. For this reason, potential barriers appear at the interface between the support substrate and the buffer layer, the interface between the buffer layer and the lower cladding layer, or the like. There is a concern that the cutoff frequency is lowered due to the accumulation of carriers in the potential well defined by the potential barrier.
[0048]
FIG. 7 shows the cutoff frequencies of the comparative example and samples E, F, and G. The horizontal axis represents the sample, and the vertical axis represents the cut-off frequency in the unit “MHz”. Circle symbols and triangle symbols in the figure indicate cutoff frequencies when the bias current is 100 mA and 50 mA, respectively.
[0049]
Samples E, F, and G have three, five, and ten InGaAs layers, respectively. It can be seen that as the number of InGaAs layers increases, the cutoff frequency decreases more significantly. Samples E and F can have a cut-off frequency of 70 MHz or higher by setting the bias current to 100 mA. Therefore, in order to realize a communication speed of 100 Mbps, it is preferable that the number of InGaAs layers in the buffer layer is 5 or less. Note that the cutoff frequencies of Samples A to D were all higher than the cutoff frequency of Sample E.
[0050]
Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.
[0051]
【The invention's effect】
As described above, according to the present invention, a buffer layer made of a semiconductor material having the same composition as the support substrate is formed on the support substrate, and the distance from the interface between the support substrate and the buffer layer to the lower surface of the active layer is increased. By setting it to 2 μm or more, the influence of crystal defects inherent in the support substrate can be reduced. Further, a buffer layer having a lattice constant larger than that of the support substrate is formed on the support substrate, and a desired semiconductor layer is grown on the buffer layer, thereby reducing the influence of crystal defects inherent in the support substrate. be able to. By forming a light emitting structure on such a buffer layer, it is possible to prevent a decrease in light output of the semiconductor light emitting device.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a semiconductor light emitting device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a substrate for explaining a method of manufacturing a support substrate of a semiconductor light emitting device according to an embodiment of the present invention.
FIG. 3 is a graph showing SIMS analysis results of a laminated structure in which an AlGaAs layer is formed by LPE on a GaAs temporary substrate and AlGaAs is formed thereon by MOCVD.
FIG. 4 is a cross-sectional view illustrating a configuration example of a buffer layer of a semiconductor light emitting device according to an example.
FIG. 5 is a cross-sectional view illustrating a configuration example of a buffer layer of a semiconductor light emitting device according to an example.
FIG. 6 is a graph showing a relationship between energization time and normalized light output of semiconductor light emitting devices according to examples and comparative examples.
FIG. 7 is a graph showing cutoff frequencies of semiconductor light emitting devices according to examples and comparative examples.
[Explanation of symbols]
1 Temporary substrate made of GaAs 2 AlGaAs high concentration layer 3 AlGaAs low concentration layer 4 Support substrate 5 Buffer layer 6 AlGaAs lower cladding layer 7 AlGaAs lower carrier confinement layer 8 AlGaAs active layer 9 AlGaAs upper carrier confinement layer 10 AlGaAs upper clad layer 11 AlGaAs current diffusion layer 12 GaAs contact layer 15 p-side electrode 16 n-side electrode

Claims (2)

A support substrate made of a semiconductor material;
A buffer layer including a layer disposed on the support substrate and formed of a semiconductor material having a lattice constant larger than that of the support substrate;
A lower carrier confinement layer disposed on the buffer layer and formed of a semiconductor material;
An active layer formed on the lower carrier confinement layer and made of a semiconductor material having a smaller band gap than the lower carrier confinement layer;
Wherein formed on the active layer, it has a upper carrier confinement layer formed of a semiconductor material having a larger band gap than the active layer,
The support substrate, the lower carrier confinement layer, and the upper carrier confinement layer are formed of a compound semiconductor material including Al and Ga as a group III element and As as a group V element, and the buffer layer includes an In ₁₋ comprising a layer formed by _{x (Al z Ga 1-z} ) x as (0 <x <1, and 0 ≦ z ≦ 1), said active layer comprises in and Ga as group III elements, V group A semiconductor light emitting device formed of a compound semiconductor material containing As as an element . A step of liquid phase epitaxial growth of a support layer made of a semiconductor material different from the temporary substrate on the surface of the temporary substrate made of a semiconductor material;
Removing the temporary substrate and leaving a support substrate comprising the support layer;
Growing a buffer layer including a layer made of a semiconductor material having a lattice constant larger than the lattice constant of the support substrate on the surface of the support substrate;
On the buffer layer, the active layer, and sandwiching the active layer, have a forming a light emitting structure including a large pair of carrier confinement layer of a band gap than the active layer,
The temporary substrate is made of GaAs, the support layer and the carrier confinement layer are made of a compound semiconductor material containing Al and Ga as group III elements and As as a group V element, and the buffer layer is made of In _1. comprising a layer formed by _{-x (Al z Ga 1-z} ) x as (0 <x <1, and 0 ≦ z ≦ 1), said active layer comprises in and Ga as group III elements, V A method of manufacturing a semiconductor light emitting device formed of a compound semiconductor material containing As as a group element .

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