JP4078891B2 - Compound semiconductor epitaxial wafer manufacturing method and compound semiconductor epitaxial wafer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a compound semiconductor epitaxial wafer and a compound semiconductor epitaxial wafer, and more particularly to an epitaxial wafer suitable for use in an optical element.
[0002]
[Prior art]
An example of a conventional semiconductor laser diode (LD) using an AlGaInP-based semiconductor material is shown in FIG. In the figure, 201 is an n-type GaAs substrate, and 202 is a clad layer made of n-type AlGaInP formed on the substrate 201. Reference numeral 203 denotes an active layer made of AlGaInP. Reference numeral 204 denotes a clad layer made of p-type AlGaInP. That is, the mixed crystal ratio is set so that the energy gap of the AlGaInP active layer 203 is smaller than the energy gap of the AlGaInP cladding layers 202 and 204, and a double heterostructure is formed. Reference numeral 206 denotes a contact layer.
[0003]
Reference numeral 205 denotes a current blocking layer made of GaAs. The current blocking layer 205 is provided for the purpose of so-called current confinement in order to obtain a current density necessary for laser oscillation. 205 is formed by selectively etching the layer 204 to form a ridge and then selectively growing it using an amorphous film such as SiNx.
[0004]
FIG. 3 shows a structure of a conventional epitaxial wafer used for an optical element such as the LD. The n-type GaInP buffer layer 2, the n-type AlGaInP cladding layer 3, the quantum well active layer 4, the p-type AlGaInP cladding layer 5, the p-type GaInP intermediate layer 6, and the p-type GaAs are sequentially formed on the n-type GaAs substrate 1. The contact layer 7 is laminated.
[0005]
The feature of this configuration is as follows. That is, aluminum, gallium, indium phosphide (p-AlGaInP) is used for the p-type cladding layer 5, and gallium arsenide (p-GaAs) is used for the p-type contact layer 7. Further, when a p-type contact layer is formed immediately above the p-type cladding layer 5, the interface becomes a resistance component due to a sudden band gap discontinuity. Indium phosphide (p-GaInP) is inserted. The carrier concentration of each of these layers is uniform within the layer.
[0006]
[Problems to be solved by the invention]
However, in the above-described prior art, a steep band gap is not formed at the interface between the p-type AlGaInP cladding layer 5 and the p-type GaInP intermediate layer 6 or the interface between the p-type GaInP intermediate layer 6 and the p-type GaAs contact layer 7. The resistance component for continuation remains. In particular, these interfaces have a tendency to increase the resistance component because a local and steep energy barrier called a notch 8 is easily formed as shown in FIG. was there.
[0007]
Accordingly, an object of the present invention is to provide an epitaxial wafer suitable for manufacturing a higher-power semiconductor laser diode and a method for manufacturing the same, in which the above-described problems are solved and the resistance component at the interface of these compound semiconductor layers is reduced. It is in.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
[0009]
A method for producing a compound semiconductor epitaxial wafer according to claim 1 is a metal organic vapor phase epitaxy method in which a compound semiconductor layer is grown by introducing a source gas, an impurity gas, and a carrier gas on a substrate heated by a heater. In the method of manufacturing a compound semiconductor epitaxial wafer in which at least an AlGaInP cladding layer, a GaInP intermediate layer, and a GaAs contact layer are continuously vapor-phase grown using the above, by increasing the amount of Zn introduced by the impurity gas, The GaP composition ratio of the compound semiconductor layer is lowered stepwise or continuously from the AlGaInP cladding layer side without changing the flow rate of the source gas.
[0010]
This includes all forms in which the gradient region or transition region of the GaP composition is arranged in the vicinity of the interface between the layers to be created. Typically, the following two forms are included. The first is a compound semiconductor epitaxial in which at least an AlGaInP cladding layer, a GaInP intermediate layer, and a GaAs contact layer are continuously grown in a vapor phase by introducing a source gas, an impurity gas, and a carrier gas onto a substrate heated by a heater. In the wafer manufacturing method, by increasing the amount of Zn introduced by the impurity gas, the GaP composition ratio of the GaInP intermediate layer is lowered stepwise or continuously without changing the flow rate of the source gas. It is a form (form of Claim 2). The second is a compound semiconductor epitaxial in which at least an AlGaInP cladding layer, a GaInP intermediate layer, and a GaAs contact layer are continuously grown in a vapor phase by introducing a source gas, an impurity gas, and a carrier gas onto a substrate heated by a heater. In the wafer manufacturing method, by increasing the amount of Zn introduced by the impurity gas, the GaP composition is formed on the GaInP intermediate layer side of the AlGaInP cladding layer without changing the flow rate of the source gas. This is a mode of forming a transition region that lowers the ratio. That is, the transition region is formed not in the intermediate layer or in the vicinity of the interface on the intermediate layer side in the cladding layer adjacent to the intermediate layer together with the intermediate layer.
[0011]
According to a second aspect of the present invention, there is provided a method for producing a compound semiconductor epitaxial wafer comprising introducing a source gas, an impurity gas, and a carrier gas onto a substrate heated by a heater, so that at least an AlGaInP cladding layer, a GaInP intermediate layer, and a GaAs contact are provided. In the method of manufacturing a compound semiconductor epitaxial wafer in which a layer is continuously vapor-grown using a metal organic vapor phase growth method, the flow rate of the source gas is increased by increasing the amount of Zn introduced by the impurity gas. The GaP composition ratio of the GaInP intermediate layer is decreased stepwise or continuously from the side of the AlGaInP cladding layer without changing.
[0012]
The compound semiconductor epitaxial wafer according to the invention of claim 3 is a compound semiconductor epitaxial wafer in which at least an AlGaInP clad layer, a GaInP intermediate layer, and a GaAs contact layer are continuously grown on a GaAs substrate by using a metal organic chemical vapor deposition method. In this case, the carrier concentration by the addition of zinc in the GaInP intermediate layer is gradually increased from the AlGaInP cladding layer side, and the zinc is added without changing the flow rate of the source gas in the metal organic chemical vapor deposition method. Then, the GaP composition ratio of the GaInP intermediate layer is grown in a stepwise or continuous manner from the AlGaInP cladding layer side.
[0013]
<Key points of the invention>
In order to achieve the above object, in the present invention, a p-type impurity, particularly zinc (Zn), is added to gallium indium phosphide (GaInP) or aluminum gallium indium phosphide (AlGaInP) grown by metal organic chemical vapor deposition. Utilizing the property that, when added, the mixed crystal composition changes.
[0014]
For example, in GaInP, when the raw material flow rates of gallium and indium are adjusted so that the lattice matching with the GaAs substrate is undoped without intentionally adding impurities, that is, the deviation of the lattice constant Δθ (delta theta) from the substrate is close to zero. When zinc (Zn) is added at the time of growth to form a p-type layer, Δθ shifts, and the rate of incorporation of gallium and indium into the growth film changes. In addition, this change changes according to the amount of zinc to be added. The higher the p-type carrier concentration in the film, the larger the shift amount of Δθ.
[0015]
This Δθ deviation may be shifted to the plus side (the direction in which the lattice constant is larger than that of the substrate) or may be shifted to the negative side (the direction in which the lattice constant is smaller than that of the substrate). However, by adjusting the growth conditions, It can be shifted to the minus side.
[0016]
When p-type gallium indium phosphide (GaInP) is grown under these conditions, zinc is added, and the addition amount is gradually increased, so that Δθ is larger than that of the undoped layer without changing the raw material flow rates of gallium and indium. It is possible to grow a layer in which the gallium composition is gradually shifted to the negative side, that is, the gallium composition is shifted to the lower side.
[0017]
As is well known, zinc is an easily diffusing element, but the rate of gallium and indium incorporation is determined during the growth of supplying zinc, so even if zinc diffuses after layer growth, The composition ratio of indium does not change.
[0018]
The conventional problems can be solved by disposing the gradient region of the composition to be produced in the vicinity of the interface between the layers.
[0019]
In Ga _x ln _x-1 P of the intermediate layer, the band gap energy Eg is reduced when the mixed crystal ratio x is reduced, and the band gap energy Eg of GaP when the mixed crystal ratio x = 0 is 2.26 ( eV). Conversely, when the mixed crystal ratio x is increased, the band gap energy Eg is increased, and when the mixed crystal ratio x = 1, the band gap energy Eg of InP is 1.35 (eV).
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on illustrated embodiments.
[0021]
As shown in FIG. 1, an n-type GaInP buffer layer 2 and an n-type (Al _0.7 Ga _0.3 ) InP clad layer 3 lattice-matched with this are epitaxially grown on an n-type GaAs substrate 1 sequentially, and undoped (Al _0.5 Ga _0.5 ) InP guide layer, quantum well active layer 4 composed of a barrier layer and strained GaInP well layer, p-type (Al _0.7 Ga _0.3 ) InP cladding layer 5, p-type GaInP intermediate layer 6, p-type GaAs contact layer 7 To grow a double heterostructure.
[0022]
Here, the thickness of the p-type GaInP intermediate layer 6 is set to 300 nm. The growth conditions of this layer are adjusted in advance by adjusting the flow rates of the gallium raw material and the indium raw material so that Δθ becomes almost zero when undoped. I left it.
[0023]
As shown in FIG. 1, when this p-type GaInP intermediate layer 6 is actually grown, after the p-type AlGaInP clad layer 5 is grown, the flow rates of the gallium source material and the indium source material are set to the values when the undoped conditions are determined. The carrier concentration of the layer by addition of zinc is 5 × 10 ¹⁷ cm ⁻³ (6-1) for the first 30 nm, 1 × 10 ¹⁸ cm ⁻³ (6-2) for the next 150 nm, and then 30 nm. 1.5 × 10 ¹⁸ cm ⁻³ (6-3), 30 nm is 2 × 10 ¹⁸ cm ⁻³ (6-4), 30 nm is 2.5 × 10 ¹⁸ cm ⁻³ (6-5), and 30 nm is 3 The growth was carried out while increasing the flow rate of zinc so as to be × 10 ¹⁸ cm ⁻³ (6-6). At this time, the deviation of Δθ was investigated separately, about 5 seconds for a layer of 5 × 10 ¹⁷ cm ⁻³ , about −50 seconds for a layer of 1 × 10 ¹⁸ cm ⁻³ , and about 3 × 10 ¹⁸ cm. It was about -600 seconds in the ^-3 layer.
[0024]
The other layers were grown under conventional growth conditions.
[0025]
Incidentally, the conventional intermediate layer was a uniform layer of gallium indium phosphide (GaInP) having a carrier concentration of 1.2 × 10 ¹⁸ cm ⁻³ and Δθ being substantially zero at this carrier concentration.
[0026]
An image of the energy band of the transition region in the intermediate layer 6 of this embodiment is shown in FIG. On the other hand, the image of the energy band of the conventional intermediate layer is shown in FIG. In the present invention, it is considered that the energy barrier called the notch 8 existing at the interface of the conventional example disappears due to the insertion of the inclined region, and the resistance component is reduced accordingly.
[0027]
When a semiconductor laser diode was manufactured using the epitaxial wafer of this embodiment, the series resistance component of the element could be reduced by 15%. Also, the oscillation threshold current of the element was reduced by 5 to 10 percent.
[0028]
In the above embodiment, the GaP composition ratio of the p-type GaInP intermediate layer 6 is decreased stepwise without increasing the flow rate of the source gas by increasing the amount of Zn introduced by the impurity gas. However, it can also be configured to continuously decrease. In addition to the above embodiment, a gradient region having the same carrier concentration can also be provided on the p-type GaInP intermediate layer 6 side in the p-type (Al _0.7 Ga _0.3 ) InP cladding layer 5, thereby Needless to say, a similar effect can be expected.
[0029]
【The invention's effect】
As described above, according to the present invention, the following excellent effects can be obtained. In other words, by using the property that the mixed crystal composition changes by adding p-type impurities, especially zinc, to GaInP grown by metalorganic vapor phase epitaxy or AlGaInP, Without changing the raw material flow rates of gallium and indium, a layer in which the gallium composition is shifted to the lower side can be grown only by changing the carrier concentration. By arranging the gradient region of the composition to be produced in the vicinity of the interface between the layers, the resistance component of the interface is reduced, and an epitaxial wafer suitable for producing a higher-power semiconductor laser diode or the like can be easily obtained. Can be produced.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view illustrating the configuration of a compound semiconductor epitaxial wafer for an optical element of the present invention.
FIG. 2 is an image diagram of an energy band of a GaInP intermediate layer in a compound semiconductor epitaxial wafer for an optical element of the present invention.
FIG. 3 is a schematic cross-sectional view showing the structure of a conventional compound semiconductor epitaxial wafer for optical elements.
4 is an image diagram of an energy band of a GaInP intermediate layer of the conventional example shown in FIG. 3;
FIG. 5 is a schematic cross-sectional view showing the structure of a conventional semiconductor laser diode.
[Explanation of symbols]
1 n-type GaAs substrate 2 n-type GaInP buffer layer 3 n-type AlGaInP cladding layer 4 quantum well active layer 5 p-type AlGaInP cladding layer 6 p-type GaInP intermediate layer 7 p-type GaAs contact layer 8 notch (energy barrier)

Claims (3)

At least an AlGaInP clad layer, a GaInP intermediate layer, and a GaAs contact layer are formed using a metal organic vapor phase growth method in which a compound semiconductor layer is grown on a substrate heated by a heater by introducing a source gas, an impurity gas, and a carrier gas. In the method for producing a compound semiconductor epitaxial wafer in which the vapor phase is continuously vapor- grown,
By increasing the amount of Zn introduced by the impurity gas, the GaP composition ratio of the compound semiconductor layer can be decreased stepwise or continuously from the AlGaInP cladding layer side without changing the flow rate of the source gas. A method for producing a compound semiconductor epitaxial wafer. By introducing a source gas, an impurity gas, and a carrier gas onto a substrate heated by a heater, at least an AlGaInP cladding layer, a GaInP intermediate layer, and a GaAs contact layer are continuously vaporized using a metal organic chemical vapor deposition method. In the method of manufacturing a compound semiconductor epitaxial wafer for phase growth,
By increasing the amount of Zn introduced by the impurity gas, the GaP composition ratio of the GaInP intermediate layer is decreased stepwise or continuously from the side of the AlGaInP cladding layer without changing the flow rate of the source gas. A method for producing a compound semiconductor epitaxial wafer, comprising: In a compound semiconductor epitaxial wafer in which at least an AlGaInP clad layer, a GaInP intermediate layer, and a GaAs contact layer are continuously grown on a GaAs substrate by using a metal organic chemical vapor deposition method .
The carrier concentration due to the addition of zinc in the GaInP intermediate layer is gradually increased from the side of the AlGaInP cladding layer, and by adding the zinc without changing the flow rate of the source gas in the metal organic chemical vapor deposition method, A compound semiconductor epitaxial wafer, wherein the GaP composition ratio of the GaInP intermediate layer is grown while decreasing stepwise or continuously from the AlGaInP cladding layer side.

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