JP3218582B2 - GaInAs photodiode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in spectral sensitivity characteristics of a photodiode using a compound semiconductor material.

[0002]

2. Description of the Related Art Conventionally, Ge (germanium) and GaInAs have been used as photodiodes in a wavelength band of 1.5 μm.
A photodiode of (germanium, indium, arsenic) is known. Ga photodiode compared to Ge photodiode
The InAs photodiode has a dark current smaller by one digit or more and has a higher spectral sensitivity in a wavelength range of 1 to 1.5 μm and is superior. GaInAs used for optical measurement and optical communication
In the photodiode, a GaInAs absorption layer having a thickness of 1 to 3 μm is formed on an InP (indium phosphorus) substrate, and an InP window layer is formed on the absorption layer.
This is a configuration formed in the GaInAs absorption layer near the interface of the InAs absorption layer. At this time, the GaInAs absorption layer is formed by controlling the composition of Ga and In (group 3 composition) so as to match the lattice constant of InP. Therefore, I
The difference in the lattice constant of GaInAs with respect to nP (lattice mismatch rate Δa / a) is approximately within ± 0.3%. The spectral sensitivity limit on the long wavelength side of such a GaInAs photodiode is determined by the absorption edge wavelength of GaInAs, and is shorter than about 1.7 μm at room temperature.

However, in the near-infrared wavelength band from 1.7 μm to about 2 μm, there is light absorption due to vibration modes of bonding groups such as CH, HN, and HO. 1.7 μm for a near-infrared analyzer for measuring
The light receiving element on the long wavelength side of m or more is particularly important.

[0004] A PbS (lead / sulfur) photoconductive element is known as a light receiving element in the 2 µm band. However, there have been problems such as the sensitivity changes with time, its temperature dependence is large, and the response speed is slow.

A photodiode whose spectral sensitivity is extended to about 1.8 μm on the longer wavelength side has a lattice mismatch rate of 0.5%.
(Wada)
Et al., Optics, July 1992, Vol. 21, No. 7, p. 2
9). The lattice mismatch relaxation layer used at this time was Ga
An InAs / InP strained lattice layer having a thickness of about 3 μm.
m and relatively thin. However, when the spectral sensitivity is extended to a longer wavelength side than 2 μm, the lattice mismatch ratio of the GaInAs absorption layer to InP exceeds 1%. The mitigation layer for such large lattice mismatch is GaInAs /
It has not been realized yet with the InP strain lattice layer.

On the other hand, a photodiode having a GaInAs absorption layer having a spectral sensitivity at a wavelength of 2 μm or more has been manufactured using InAsP as a lattice mismatch relaxation layer (K. Maki).
ta et al., Electronic Letters, vol. 24, p. 379, 198
8. and KRRinga, et al., J. Lightwave Technology,
vol.10, p.1050, 1992.). The lattice mismatch relaxation layer used here has a composition y of InAs _Y P _1-Y from the InP substrate side.
Buffer layer (graded
composition InAs _Y P _1-Y buffer layer).
Although the structure of these buffer layers shown in FIG. 5 is effective in reducing the dislocation density of the lattice mismatch grown layer, the thickness of the compositionally graded InAsP buffer layer is 15 to 2
It is very thick at 0 μm. For this reason, it is necessary to shorten the crystal growth time, and the hydride (hydr) having a high crystal growth rate is required.
ide) Vapor phase epitaxy (VPE) was used.

However, in the hydride VPE method, the crystal growth rate is high, but the submicron film thickness controllability of less than 1 μm is controlled by the metal organic vapor phase epitaxy method (MOVPE: metalo).
rganic vapor phase epitaxy). Therefore, such a thick composition gradient InAsP
It has been basically difficult to manufacture a photodiode having a configuration including a buffer layer and a layer having a submicron thickness. Also, forming such a thick buffer layer for the manufacture of a photodiode has been a great constraint on the manufacturing process when elements other than the photodiode are integrated on one substrate.

[0008]

By changing the group III composition of GaInAs of a GaInAs photodiode,
When the spectral sensitivity is extended to a wavelength near 2 μm by changing the absorption edge wavelength of the As absorption layer to the longer wavelength side, GaIn
The lattice constant of the As absorption layer becomes larger than that of InP, and lattice mismatch occurs.

[0009] The present invention relates to a lattice of the GaInAs absorption layer.
InAs mismatch_XP_1-X/ InAs _YP_1-YCombination of
Of the conventional superlattice layer was inserted in multiple stages.
A layer that relaxes with a thickness of 1/3 or less compared to the buffer layer
And the lattice constant of the GaInAs absorption layer and -0.5 to
InAsP window with lattice constant matched at 0.5%
By forming the layer with a thickness of 0.1 μm or less, 1 μm
high spectral sensitivity from the shorter wavelength side to near 2 μm
To provide highly reliable photodiodes
It is the target.

[0010]

A buffer is provided on an InP substrate.
Layer, a light absorption layer, and a window layer in this order.
A photodiode, wherein the buffer layer is
InAs _x P _1-x layer with lattice constant larger than P substrate and I
Strained superlattice in which nAs _y P _1-y layers are alternately stacked in multiple stages
Layer and the light absorbing layer have a lattice mismatch rate with the InP substrate.
0.5% or more GaInAs layer, the window layer is the GaI
Lattice constant with nAs absorption layer is -0.5 to 0.5%
It is characterized in that it is a layer having a thickness of 0.1 μm or less .

[0011]

The lattice mismatch relaxation layer in which the strained superlattice layer of the combination of InAs _X P _1-X / InAs _Y P _1-Y is inserted in multiple stages,
A growth method having a relatively low growth rate such as the MOVPE method can be applied.
The thickness of the nAsP window layer can be accurately controlled and formed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the GaInAs photodiode of the present invention. As shown in FIG. 1, the GaInAs photodiode having the configuration of the present embodiment has n +-(10
0) on the InP substrate, n + -InP layer, InAs _y P _1-y
/ InAs _z P _1-z strained superlattice buffer layer, n-Ga _1-x
An In _x As absorption layer, n-InAs _x ^, P _1-x ^{, and a} window layer are sequentially grown by MOVPE, and p is selectively diffused by Zn.
+ Regions absorbent layer, the absorbent layer / window layer fabricated as p + -n junction is formed near the interface, the p + side and the substrate rear surface n
The electrode (for example, Au-Zn, Au-Sn
Alloy electrode) and an antireflection film is provided on the light receiving surface. FIG. 2 shows the lattice mismatch rate (horizontal axis) with respect to InP changed in the film growth direction (vertical axis).

Here, InAs grown by the MOVPE method is used.
_{Y '}P_{1-Y '}AsH_Three(Arsine) flow rate and PH_Three(Foss
Fin) flow rate (converted to concentration 100%) ratio: As / (As + P) ≡AsH_ThreeFlow rate / (AsH_ThreeFlow rate +
PH_ThreeLattice mismatch rate for InP: Δa / a≡ (InAs_{Y '}P_{1-Y '}Lattice constant-InP lattice constant
FIG. 2 shows the result of an experiment to determine the relationship between (number) / InP lattice constant × 100 (%). TMI
(100) I
It was epitaxially grown on an nP substrate. InAs _{Y '}P
_{1-Y '}The growth rate of the epitaxial film is 10 to 20 (nm)
/ Min), and can be precisely controlled by changing the TMI flow rate.
You. As shown in FIG. 2, the lattice mismatch is reduced to about 2%.
Control with constant reproducibility can be performed. In addition, the V-group composition Y ′ changes.
Of InAs_{Y '}P_{1-Y '}The change in the absorption edge wavelength of
(Nagai et al., “3-V Group Semiconductor Mixed Crystal,” Corona Co., Ltd.
Chapter, pp. 27-47).

On the other hand, when the group _X composition of Ga _X In _{1 -X} As is changed to change the absorption edge wavelength λ _g , λ _g =
At 1.8 μm, the lattice mismatch ratio Δa / a of Ga _x In ₁ -x As to InP is about 0.5%, and λ _g = 2.2 μm.
At the time of m, Δa / a is about 1.4% (Wada et al.,
"Optics", Vol. 21, No. 7, July 1992, p. 2
9). The growth rate of the Ga _x In _1-x As epitaxial film is about 15 to 25 (nm / min), and is accurately controlled by the supply amount of the group 3 organometallic material. It has been shown that the thickness of these epitaxial films in MOVPE growth can be controlled with good reproducibility to 1 nm or less (M. Wa
da et al., Japanese Journal of Applied Physics, vo
l.29, p.2342, 1990).

[0015] Figure 3, n ⁺ - (100) on an InP substrate, n ⁺ -InP layer, n-type (S added) InAs _Y P _1-Y /
MOAs of InAs _Z P _1-Z strained superlattice buffer layer in multiple stages
Grown by the PE method, and then with an In lattice with a lattice mismatch rate of 1.7%.
Shows a cross sectional secondary electron microscope image of the growth layer when 650nm grow _{As X 'P 1-X'} . Here, GaIn is used to understand the punctuation of each strained superlattice layer grown in four stages.
5 nm of the As layer was inserted as a marker, and in the cross-sectional image, GaI was mixed with an etching solution obtained by mixing sulfuric acid, hydrogen peroxide solution, and water.
The nAs layer is being etched. In in each strained superlattice layer
The thickness of AsP is 80 nm. This epitaxial wafer has no warp and has a lattice mismatch rate Δa with InP.
/ A is, to achieve a flat growth up to 1.7%, the Ga _X
A buffer layer for growing an In _1-x As absorption layer (Δa / a> 1%) is formed.

As described above, in the above embodiment, the thickness of the buffer layer for alleviating the lattice mismatch can be extremely reduced to 1/3 or less (5 μm or less) of the conventional one. In the GaInAs photodiode of the present invention shown in FIG.
There is no particular need to insert the nAs marker layer.

[0017] The thickness of the _{n-Ga X In 1-X} As absorbing layer having a lattice constant approximately equal to the lattice constant of the top of the InAs _{X 'P 1-X'} layer of the buffer layer for lattice mismatching buffer Sa2
After the growth of μ3 μm, the difference in lattice constant between the n-InAs _{X ′} P _{1 -X ′} window layer and the window layer and the absorption layer is approximately −0.5 to
It is formed so as to have a thickness of 0.5% or less and a thickness of 0.1 μm or less. In particular, the window thickness is critical thickness (JWMatthews and A.
E. Blakeslee, Journal of Crystal Growth vol. 27, p. 11
1, 1974), crystal defects do not occur due to lattice mismatch between the absorption layer and the window layer, and the reliability is high.

In such a structure, the spectral sensitivity of the GaInAs photodiode is as follows (Wada et al., “Optical” 1).
July 1999, Vol. 21, No. 7, p. It can be calculated in detail using the model of 29). In the GaInAs photodiode of the present invention shown in FIG. 1, the antireflection film is a _two- layer film of SiO ₂ (0.18 μm in thickness) / Si ₃ N ₄ (0.17 μm in thickness), and λ _g = 2.2 μm. Ga
InAs absorption layer (2 μm thick), InA having the same Δa / a as lattice mismatch Δa / a = 1.4% of GaInAs
If an sP window layer is used, the spectral sensitivity calculation result shown in FIG. 4 is obtained. In FIG. 4, the InAsP window layer thickness: 0.1, 0.5, 1
Calculated for three μm.

When the thickness of the InAsP window layer is large, the light absorption by the window layer increases from the absorption edge wavelength of about 1.3 μm to the short wavelength side of the window layer, and the light absorption by the window layer decreases. The unevenness of the spectral sensitivity due to light interference on the long wavelength side also increases. Therefore, when the InAsP window layer is thin, over a wide wavelength range of 0.6 to 2 μm or more,
A GaInAs photodiode having high spectral sensitivity can be realized with a configuration of a buffer layer that is much thinner than before.

[0020]

As described above in detail with the embodiments, according to the present invention, a thin buffer layer having a structure in which a strained superlattice structure of InAsP is inserted in multiple stages is used.
A GaInAs absorption layer having a lattice mismatch with nP of 1% or more is formed, and the window layer is formed of InAs having a thickness of 0.1 μm or less.
By using P, a GaInAs photodiode having high spectral sensitivity in a wavelength range larger than 0.6 to 2 μm can be realized. In addition, the Ga of the present invention
The thickness of the buffer layer used for the InAs photodiode is 5 μm or less, and M
The OVPE growth method can be applied, and when other elements are integrated on the same substrate, the etching depth can be reduced, and the restrictions on the manufacturing process, such as flattening technology such as trench filling with polyimide, are greatly eased. A GaInAs photodiode having the above effect can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a GaInAs photodiode of the present invention.

FIG. 2 is a diagram showing a relationship between a group V molar flow ratio and a lattice mismatch ratio.

FIG. 3 is a cross-sectional secondary electron microscope image of a growth layer of a GaInAs photodiode according to the present invention.

FIG. 4 is an example of a calculation result of spectral sensitivity of the GaInAs photodiode of the present invention.

FIG. 5 is a configuration diagram of a conventional example.

Claims (1)

(57) [Claims] A buffer layer and a light absorbing layer on an InP substrate;
A GaInAs photodiode in which window layers are sequentially stacked
And the buffer layer has a larger lattice constant than the InP substrate.
InAs _x P _1-x layers and InAs _y P _1-y layers having
The strained superlattice layer and the light absorbing layer stacked in a step have a lattice mismatch ratio of 0.5 with the InP substrate.
5% or more of the GaInAs layer, and the window layer has a lattice constant with the GaInAs absorption layer of −
A film thickness of 0.1 μm that is matched at 0.5 to 0.5%
The following layers. A GaInAs photodiode characterized by the above-mentioned.