JPS6262477B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a composite semiconductor device in which a light receiving element and a field effect transistor (hereinafter abbreviated as FET) element are provided on one GaAs substrate.

Attempts have already been made to create a composite semiconductor device in which a photodiode is formed on a GaAs substrate, and an FET and the like for amplifying a signal current obtained from the photodiode, arithmetic processing, etc. are formed on the same GaAs substrate.

FIG. 1 is a sectional view showing an example of the composite semiconductor device according to the prior art. In Figure 1, area A
is the light receiving element part, and area B is the FET element part,
The photodetector is made by diffusing zinc (Zn) etc. to a depth of about 1 μm on a semi-insulating n-GaAs substrate 1.
A P ⁺ layer 2 is formed, and an electrode 3 is formed from the P ⁺ layer, and n-GaAs
It is formed by providing another electrode 4 on the substrate 1. In addition, the FET element has an n + -GaAs layer 5 with a carrier concentration of about 1×10 ¹⁷ cm ^-13 on an n ^- GaAs substrate 1.
The source electrode 6 is grown to a thickness of about 0.2 μm.
and the drain electrode 7 is made of gold germanium (AuGe).
etc., and by disposing the gate electrode 8 using aluminum (Al) or the like,
Thereafter, an insulating layer and a desired wiring pattern are provided.

In the composite semiconductor device having the structure described above, the semi-insulating GaAs substrate 1 constitutes the active layer of the light-receiving element, and an element isolation effect between the FET element, the light-receiving element, and the FET elements is desired. , because the photodetector does not have a window layer, the recombination and surface bonding of carriers generated by the incident light in the P ⁺ layer are large on the short wavelength side, and the quantum efficiency is large on the short wavelength side, as shown in Figure 2. There is a drawback that it drops significantly on the side. Furthermore, the isolation between elements is not sufficient and it is necessary to improve insulation.

An object of the present invention is to improve the quantum efficiency by providing a window layer on the light receiving element in a composite semiconductor device in which a light receiving element and a FET element are provided on one GaAs substrate, and to create a structure that improves the insulation between the elements. Our goal is to provide the following.

The object of the present invention is that the GaAs layer serving as the active layer of the FET element is formed by forming a semi-insulating AlxGa ₁ - on the GaAs substrate.
Formed through an xAs (0<X≦1) layer,
This is achieved by making the AlxGa ₁ -xAs layer constitute the window layer of the photodetector, and by mesa-etching the layer formed on the GaAs substrate around the photodetector, the photodetector and the FET element group can be separated. Become complete.

Hereinafter, the present invention will be specifically described by way of examples with reference to the drawings.

FIG. 3 is a sectional view showing a first embodiment of the present invention. As shown in FIG. 3, a ^molecular beam epitaxial growth method (hereinafter referred to as
The n-GaAs layer 12 with a carrier concentration of about 5×10 ¹⁶ cm ^-3 or more is formed to a thickness of about 3 μm by using a vapor phase epitaxial growth method (abbreviated as MBE method) or vapor phase epitaxial growth method (hereinafter abbreviated as VPE method). Semi-insulating n ^- - with a concentration of about 1 x 10 ¹⁴ cm ^-3 or less
An Al0.3Ga0.7As layer 13 is grown to a thickness of about 2 μm, and an n ⁺ -GaAs layer 14 having a carrier concentration of about 1×10 ¹⁷ _cm ⁻³ is grown to a thickness of about 0.2 μm.

After that, n ⁺ of the area A where the light receiving element is formed.
- Selectively remove the GaAs layer 14 and use silicon dioxide (SiO ₂ ) as a mask to add Zn to the n ^- -Al0.3Ga0.7As layer 13 at a concentration of about 10 ¹⁸ to 10 ¹⁹ cm ^-3 and a depth of 1
The P ⁺ region 15 is provided by diffusing to about μm.

Regarding the FET element region B, the n ⁺ -GaAs layer 14 is separated into each element by a normal photolithography method, and a source 16, a drain 17, and a gate 18 are formed respectively. Note that electrodes 19 and 20 are also provided on the P region 15 and the n ⁺ -GaAs substrate 11 for the light receiving element.

After that, the area around the light-receiving element area A, especially this area, is
n ^- -Al0.3Ga0.7As layer 1 between FET element area B
3 and the n-GaAs layer 12 are selectively removed, and mesa etching is performed to separate the light receiving element and the FET element.

As described above, the GaAs pin photodiode and GaAs with the n ^- -Al0.3Ga0.7As layer 13 as the window layer
FETs are formed on the same GaAs substrate.

FIG. 4 is a sectional view showing a second embodiment of the present invention. In this embodiment ^, a semi-insulating GaAs substrate is used as the substrate ^.
The GaAs layer 22 is made to have a thickness of about 3 μm, and then ^a semi-insulating layer with a carrier concentration of about 1×10 ¹⁴ cm ^-3 or less
The AlxGa ₁ -xAs layer 23 has a thickness of about μm, and the n ⁺ -GaAs layer 2 has a carrier concentration of about 1×10 ¹⁷ cm ^-3 .
4 was formed to a thickness of about 0.2 μm by the MBE method or the VPE method, and each element was provided in the same manner as in the first embodiment. However, in this second embodiment, part of the mesa etching around the light receiving element area A other than the FET element area B side is n ^- -
Only the AlxGa ₁ -xAs layer 23 is used, and the photodiode n-side electrode 25 is provided on the n-GaAs layer 22.

According to this second embodiment, the light receiving element area A and
The isolation and insulation between the FET element region B and the FET element region B is improved compared to the first embodiment.

FIG. 5 is a sectional view showing a third embodiment of the present invention. In this embodiment, an n ⁺ −GaAs layer 3 with a carrier concentration of about 1×10 ¹⁷ cm ⁻³ is formed on a semi-insulating GaAs substrate 31.
2 to a thickness of about 2 μm, and then the carrier concentration was
10 ¹⁴ cm ^-3 semi-insulating GaAs layer 33 with a thickness of 3μ
After that, the semi-insulating n ^- -AlxGa ₁ -xAs layer 34 and the n ⁺ -GaAs layer 3 are formed as in the previous example.
5, and by mesa etching around the light receiving element area A, only the semi-insulating GaAs substrate 31 is left on the FET element area B side, and the n ⁺ -GaAs layer 32 is left in a part, and a photodiode is formed. This is an example in which an n-side electrode 36 is provided.

According to this third embodiment, the isolation and insulation between the FET elements and between the FET element and the light receiving element are further improved, and the quantum efficiency of the photodiode is also improved.

FIG. 6 is a chart showing an example of the quantum efficiency obtained for the first example, in which the horizontal axis shows the wavelength (nm) of the incident optical signal, the vertical axis shows the quantum efficiency (%), and Compared to the conventional technique shown in Figure 2, an increase in quantum efficiency of about 20% is observed at a wavelength of 700 nm, and a high quantum efficiency that is almost flat in the band of 100 nm or more is obtained.

Insulation between elements is provided by a GaAlAs layer, which can provide better insulation than GaAs.

As explained above, the present invention provides a composite semiconductor device in which a light receiving element and a FET element are provided on one GaAs substrate, in which a semi-insulating AlxGa ₁ -xAs is used for the light receiving element.
By forming a GaAs layer, which constitutes the active layer of the FET element, through the AlxGa ₁ -xAs layer, the quantum efficiency of the light receiving element is improved and the isolation and insulation between each element is improved. Furthermore, by mesa-etching the periphery of the light-receiving element, the light-receiving element and the FET element group are completely separated, and this provides a great improvement effect on the composite semiconductor device.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment according to the prior art;
FIG. 2 is a chart showing an example of the quantum efficiency of a light receiving element according to the prior art, FIGS. 3 to 5 are cross-sectional views showing an embodiment of the present invention, and FIG. 6 is an example of the quantum efficiency of a light receiving element according to the present invention. This is a chart showing the following. In the figure, 1 is a GaAs substrate, 2 is a P ⁺ layer, 3 is an electrode, 4 is an electrode, 5 is a GaAs layer, 6 is a source electrode, 7 is a drain electrode, 8 is a gate electrode, and 11 is a
n ⁺ -GaAs substrate, 12 is n-GaAs layer, 13 is n ^-
-Al0.3Ga0.7As layer, 14 is n ⁺ -GaAs layer, 15 is
P ⁺ region, 16 source, 17 drain, 18
is a gate, 19 is an electrode, 20 is an electrode, 21 is a
GaAs substrate, 22 is n-GaAs layer, 23 is n-
AlxGa ₁ -xAs layer, 24 is n ⁺ -GaAs layer, 25 is electrode, 31 is semi-insulating GaAs substrate, 32 is n ⁺ -
GaAs layer, 33 is GaAs layer, 34 is n ^- -AlxGa ₁ -
An xAs layer, 35 an n ⁺ -GaAs layer, and 36 an electrode.

Claims (1)

[Claims] 1. In a composite semiconductor device in which a light receiving element and a field effect transistor element are provided on one GaAs substrate, the GaAs layer constituting the active layer of the field effect transistor element is formed on the GaAs substrate by AlxGa ₁ −xAs
(0<X≦1) layer, and the AlxGa ₁ −
A composite semiconductor device characterized in that an xAs layer constitutes a window layer of the light receiving element. 2. The composite semiconductor device according to claim 1, wherein at least a portion of the layer formed on the GaAs substrate is selectively removed around the light receiving element.