JPH0774381A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To obtain a semiconductor photodetector with a fast response speed for irradiation with light by increasing the mobility of positive holes. CONSTITUTION:In0.53-xGa0.47+xAs distortion superlattice layer 4a is formed on n-type InP buffer layer 3, In0.53+xGa0.47-xAs distortion superlattice layer 4b is formed on it to form a pair, and a number of pair structures are laminated; thus forming a light absorption layer, where the conditions of X expressing the composition ratio of the superlattice layer is X>0. Therefore, since the effective mass of carriers generated due to incident light in a light absorption layer can be reduced, thus increasing the response speed for the irradiation with light due to increase in the mobility of carriers at the light absorption layer. Also, since mutual stresses can be canceled by alternately laminating first and second distortion superlattice layers, the damage of light absorption layer due to stress can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving element,
In particular, it relates to a semiconductor light receiving element capable of high-speed response.

[0002]

2. Description of the Related Art FIG. 7 is a sectional view showing the structure of a conventional InGaAs semiconductor light receiving element. In FIG. 7, an n ⁺ InP contact layer 2 is formed on a semi-insulating InP substrate 1, and a positive electrode 8 that gives a positive potential is formed on the surface of the n ⁺ InP contact layer 2. n type InP on the n ⁺ InP contact layer 2
The buffer layer 3 is formed. An In _0.53 Ga _0.47 As light absorption layer 4 is formed on the n-type InP buffer layer 3, and an n-type InP window layer 5 is formed thereon. A p-type diffusion region 6 is provided inside the n-type InP window layer 5, and a negative electrode 9 for contacting the region and applying a negative potential is provided with an insulating film 7.
It is formed sandwiching.

Next, the operation will be described with reference to FIG.
By applying a positive potential and a negative potential to the positive electrode 8 and the negative electrode 9, respectively, a reverse bias voltage is applied to this light receiving element. In this state, as shown in FIG.
Light (indicated by hν) is incident from the n-type InP window layer 5
_When reaching the _0.53 Ga _0.47 As light absorption layer 4, a hole-electron pair is generated there. The generated holes travel toward the p-type diffusion region 6 due to the applied bias, and the electrons travel toward the n-type InP buffer layer 3 in reverse, so that the photocurrent flows between the positive electrode 8 and the negative electrode 9. Will flow. If this current is taken out as an output, it is possible to obtain an electric signal that is turned on / off depending on the presence or absence of light irradiation.

[0004]

Since the conventional semiconductor light receiving element is constructed as described above, the response speed of the electric signal output to the light irradiation is, except for the delay due to the capacitance (C) and the inductance (L), In _0.53 Ga _0.47 As is limited by the traveling speed of electrons and holes generated in the light absorption layer 4. Generally, since the effective mass of electrons is light and the effective mass of holes is heavy, the mobility of holes is small, which limits the response speed.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a semiconductor light receiving element having a high response speed to light irradiation by increasing the mobility of holes.

[0006]

A first aspect of a semiconductor light receiving element according to the present invention is a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and the first semiconductor layer. And a light absorption layer formed between the second light absorption layer and the second semiconductor layer, wherein the light absorption layer is In _0.53-X Ga
_A first strained superlattice layer made of _{0.47 + X} As and having a tensile stress, and a second strained superlattice layer made of In _{0.53 + X} Ga _0.47-X As and having a compressive stress are alternately laminated in multiple layers. It is characterized by being done.

A second aspect of the semiconductor light receiving element according to the present invention is a first conductivity type first semiconductor layer, a second conductivity type second semiconductor layer, the first semiconductor layer and the second semiconductor layer. In the semiconductor light receiving element having a light absorption layer formed between the two, the light absorption layer is In _0.53-X Ga _{0.47 + X} As _Y P
_{A first} strained superlattice layer formed of _1-Y and having a tensile stress;
A semiconductor light-receiving element characterized by being formed by alternately laminating a large number of second strained superlattice layers formed of In _{0.53 + X} Ga _0.47-X As _Y P _1-Y and having a compressive stress.

[0008]

According to the first aspect of the semiconductor light receiving element of the present invention, In _0.53-X Ga having a tensile stress in the light absorption layer is used.
_{0.47 + X} As first strained superlattice layer and I with compressive stress
By forming the second strained superlattice layer of n _{0.53 + X} Ga _0.47-X As, the effective mass of carriers generated by incident light in each strained superlattice layer is reduced, so that carriers in the light absorption layer are reduced. Mobility becomes large, and mutual stress can be canceled by alternately stacking the first and second strained superlattice layers.

According to the second aspect of the semiconductor light receiving element of the present invention, In _0.53-X G having a tensile stress in the light absorption layer.
a _{0.47 + X} As _Y P _1-Y first strained superlattice layer and In _{0.53 + X} Ga _0.47-X As _Y P _1-Y second strained superlattice layer each having a compressive stress. Since the effective mass of carriers generated by incident light in the strained superlattice layer of is reduced, the mobility of carriers in the light absorption layer increases,
Moreover, mutual stress can be canceled by alternately stacking the first and second strained superlattice layers, and by containing P, it becomes possible to react with light in a shorter wavelength range. Become.

[0010]

1 is a sectional view showing a first embodiment of a semiconductor light receiving element according to the present invention. In FIG. 1, an In _0.53-X Ga _{0.47 + X} As strained superlattice layer 4a is formed on the n-type InP buffer layer 3, and an In _{0.53 + X} Ga _0.47-X is formed thereon.
As strained superlattice layers 4b are formed to form a pair, and a large number of the paired structures are stacked to form a light absorption layer. here,
The strained superlattice layer is MOCVD (Metal Organic Chemical Vap
or Deposition) method or VPE (Vapor Phase Ep)
itaxy) method or MBE (Molecular Beam Epitax)
The condition of X which is formed by the y) method and represents the composition ratio of the strained superlattice layer is X> 0. Other configurations are similar to those of the conventional semiconductor light receiving element described in FIG. The basic operation of obtaining an output signal in response to light irradiation is also the same as that of the conventional semiconductor light receiving element described in FIG.

Next, referring to FIGS. 2 and 3, In _0.53-X
Ga _{0.47 + X} As strained superlattice layer 4a and In _{0.53 + X} Ga
_{The operation of the 0.47-X} As strained superlattice layer 4b will be described. I
Comparing n and Ga at the atomic level, In has a larger atomic number, so the atomic radius is approximately 3 of the atomic number.
It grows in proportion to the root. Figure 2 shows In _0.53-X Ga
The structure of _{0.47 + X} As strained superlattice layer 4a, FIG. 3 is an In _{0.53 + X}
It is the figure which represented typically the structure of _Ga0.47- XAs strained superlattice layer 4b. In FIG. 2, when Ga having a small number of atoms is rich, it receives a force to be pulled from the surroundings,
Tensile stress is applied to the entire layer. On the contrary, as shown in FIG. 3, when In having a large number of atoms is rich, it is compressed so as to be crushed from the surroundings, so that a compressive stress is applied to the entire layer.

In _0.53-X Ga _{0.47 + X under} tensile stress
As strained superlattice layer 4a and In _{0.53 + X} G to which compressive stress is applied
Since the a _0.47-X As strained superlattice layers 4b are alternately laminated, the respective stresses are canceled in the light absorption layer formed of these layers, and the light absorption layer as a whole is in a stress-free state.

Next, the hole mobility in the GaAs strained superlattice layer will be described with reference to FIGS. For details on the following description, see "IEEE J. Qantum El
ectron., vol.25, PP171-178,1989, TCChong and CGF
onstad, ”Teoretical Gain of Streined Layer Semicond
uctor Lasers in the Large Strein Regime ””.

The energy E of holes is expressed by the following equation.

[0015]

[Equation 1]

In the equation (1), Ev represents the energy at the top of the valence band and m ^* represents the effective mass of holes. h'is the Planck's constant h divided by 2π (h / 2π),
k _vec is a wave vector.

When the effective mass m ^{* of} holes is calculated from the equation (1), it is expressed by the following equation.

[0018]

[Equation 2]

FIG. 4 shows Ek curves with and without strain due to tensile stress. 4, the vertical axis represents hole energy E, the left horizontal axis represents the wave number k _H in the plane of the superlattice layer, and the right horizontal axis represents the vertical wave number k _P of the superlattice layer.
Represents In FIG. 4, the broken line represents the characteristics of the valence band of the superlattice layer when there is no strain, and the solid line represents the characteristics of the valence band when there is strain due to tensile stress. When there is no distortion, the change in the energy E of the holes with respect to the change in the wave number is gradual and shows a symmetrical characteristic. On the other hand, if strain occurs due to tensile stress, the energy of the valence band shifts, and the band gap shrinks. In addition, the characteristic is that the energy E of the hole with respect to the change of the wave number in the plane rather than in the vertical direction.
Changes sharply, and the curvature at k = 0 becomes steep as a whole. This means that the denominator on the right side becomes larger in the equation (2), and the effective mass m ^{* on the} left side becomes smaller.

FIG. 5 shows Ek curves with and without strain due to compressive stress. 5, the vertical axis represents the hole energy E, the left horizontal axis represents the wave number k _H in the plane of the superlattice layer, and the right horizontal axis represents the vertical wave number k _P of the superlattice layer. In FIG. 5, the broken line represents the characteristics of the valence band of the superlattice layer when there is no strain, and the solid line represents the characteristics of the valence band when there is strain due to compressive stress. When there is no distortion, the change in the energy E of the holes with respect to the change in the wave number is gradual and shows a symmetrical characteristic. On the other hand, if strain occurs due to compressive stress, the energy of the valence band shifts, and the band gap shrinks. Further, the characteristic is that the change of the hole energy E with respect to the change of the wave number in the vertical direction is steeper than that in the plane, and the curvature at k = 0 becomes steep as a whole. This means that the denominator on the right side becomes larger in the equation (2), and the effective mass m ^{* on the} left side becomes smaller. Further, in both cases of tensile stress and compressive stress, as the stress becomes stronger, the curvature at k = 0 becomes steeper, and the effective mass m ^* becomes smaller accordingly.

Although it has been shown above that the response speed to light irradiation is governed by the hole mobility, the relationship between the hole mobility μ _h and the effective mass m ^* is expressed as follows.

[0022]

[Equation 3]

In equation (3), τ _h is the relaxation time,
It shows the time until the momentum of holes decreases to 1 / e. Therefore, it can be seen that the mobility of holes becomes faster as the effective mass m ^* becomes smaller.

In the present embodiment, the tensile stressed In
_{Since the} light absorption layer is formed by the _0.53-X Ga _{0.47 + X} As strained superlattice layer 4a and the compressive stressed In _{0.53 + X} Ga _0.47-X As strained superlattice layer 4b, no stress is applied. In any of the layers, the effective mass m ^{* of} holes is reduced as compared with the InGaAs layer, and the mobility of holes is increased, whereby a semiconductor light receiving element having a high response speed to light irradiation can be obtained.

In this embodiment, the In _0.53-X Ga _{0.47 + X} As strained superlattice layer 4a to which a tensile stress was applied and the In _{0.53 + X} Ga _0.47-X As strained superlattice layer 4b to which a compressive stress was applied were formed. Since the light absorbing layers are alternately laminated, the tensile stress and the compressive stress are canceled even if the thickness of the entire light absorbing layer is, for example, about 2.5 μm, which is sufficient to absorb light, It becomes a stress-free state, and it is possible to prevent the crystal of the light absorption layer from being broken by the stress.

FIG. 6 shows a second semiconductor light receiving element according to the present invention.
It is sectional drawing which shows the Example of. In FIG. 6, n-type InP
An n-type InP buffer layer 12 is formed on the substrate 11. In _0.53-X G is formed on the n-type InP buffer layer 12.
a _{0.47 + X} As strained superlattice layer 13a is formed, and In _{0.53 + X} Ga _0.47-X As strained superlattice layer 13b is formed thereon to form a pair, and a large number of these paired structures are stacked to absorb light. Layer 13
Are formed. Here, the condition of X representing the composition ratio of the superlattice layer is X> 0. On top of these superlattice layers are p-type I
An nP contact layer 14 is formed, and a negative electrode 16 that gives a negative potential is formed on the surface thereof. Positive electrode 15 is n
It is formed on the lower surface side of the type InP substrate 11.

Next, the operation will be described with reference to FIG.
By applying a positive potential and a negative potential to the positive electrode 15 and the negative electrode 16, respectively, a reverse bias voltage is applied to this light receiving element. In this state, as shown in FIG. 6, when light (indicated by hν) enters from the side surface of the light absorption layer 13, holes and electron pairs are generated in the light absorption layer 13. The generated holes are p-type I due to the applied bias.
The electrons travel toward the nP contact layer 14 and the electrons are reversed to n.
Since it travels toward the type InP buffer layer 12, a photocurrent flows between the positive electrode 15 and the negative electrode 16. In _0.53-X Ga _{0.47 + X with} tensile stress
As strained superlattice layer 13a and In to which compressive stress is applied
_The effect of reducing the effective mass m ^* of holes in the _{0.53 + X} Ga _0.47-X As strained superlattice layer 13b is the same as that of the first embodiment.

In the present embodiment, the thickness of the light absorption layer 13 is set to, for example, about 0.1 μm, the traveling distance of electrons and holes is shortened, and the response speed to light irradiation is further increased. Further, since the thickness of the light absorption layer 13 is thin, the structure is such that the light is incident from the end face in order to sufficiently absorb the light.

Also in this embodiment, as in the first embodiment,
In _0.53-X Ga _{0.47 + X} As strained superlattice layer 13a to which tensile stress was applied and In _{0.53 + X} Ga to which compressive stress was applied
_{Since the 0.47-X} As strained superlattice layers 13b are alternately laminated, the tensile stress and the compressive stress are cancelled, and a stress-free state is obtained as a whole, so that the damage of the crystal of the light absorption layer 13 due to the stress can be prevented. it can.

Both the first and second embodiments of the semiconductor light receiving element according to the present invention described above can be modified as described below. That is, the superlattice layer having tensile stress is formed of In _0.53-X Ga _{0.47 + X} As _Y P _1-Y strained superlattice layer, and the superlattice layer having compressive stress is In _{0.53 + X} Ga.
The same effect as in the first and second embodiments can be obtained also by forming the _0.47-X As _Y P _1-Y strained superlattice layer, and the semiconductor light receiving element described in the above-mentioned embodiments can be obtained. It is possible to obtain a semiconductor light receiving element that responds to light in a shorter wavelength range.

[0031]

According to the semiconductor light receiving element of the first aspect, since the effective mass of the carriers generated by the incident light in the light absorption layer is reduced, the mobility of carriers in the light absorption layer is increased and The response speed to irradiation can be increased, and mutual stress can be canceled by alternately stacking the first and second strained superlattice layers, so that the light absorption layer is prevented from being damaged by the stress. You can

According to the semiconductor light receiving element of claim 2,
Since the effective mass of the carriers generated by the incident light in the light absorption layer is reduced, the mobility of the carriers in the light absorption layer is increased, and the response speed to light irradiation can be increased, and the first and second Mutual stress can be canceled by alternately stacking the two strain superlattice layers,
It is possible to prevent destruction of the light absorption layer due to stress. Further, since the light absorption layer is formed of an In _0.53-X Ga _{0.47 + X} As _Y P _1-Y strained superlattice layer and an In _{0.53 + X} Ga _0.47-X As _Y P _1-Y strained superlattice layer, P is It is possible to obtain a semiconductor light receiving element that responds to light in a shorter wavelength range than when not containing it.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of a semiconductor light receiving element according to the present invention.

FIG. 2 is a schematic diagram illustrating the structure of an In _0.53-X Ga _{0.47 + X} As strained superlattice layer.

FIG. 3 is a schematic diagram illustrating the structure of an In _{0.53 + X} Ga _0.47-X As strained superlattice layer.

FIG. 4 is a diagram showing Ek curves with and without strain due to tensile stress.

FIG. 5 is a diagram showing Ek curves with and without strain due to compressive stress.

FIG. 6 is a sectional view showing a second embodiment of the semiconductor light receiving element according to the present invention.

FIG. 7 is a sectional view showing a conventional semiconductor light receiving element.

[Explanation of symbols]

4a, 13a In _0.53-X Ga _{0.47 + X} As strained superlattice layer 4b, 13b In _{0.53 + X} Ga _0.47-X As strained superlattice layer 11 n-type InP substrate 12 n-type InP buffer layer 13 Optical absorption layer 14 p-type InP contact layer 15 Positive electrode 16 Negative electrode

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[Procedure amendment]

[Submission date] January 21, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction content]

[Figure 7]

Claims (2)

[Claims] 1. A first conductive type first semiconductor layer, a second conductive type second semiconductor layer, and a light absorption layer formed between the first semiconductor layer and the second semiconductor layer. In the semiconductor light receiving element, the light absorption layer includes a first strained superlattice layer formed of In _0.53-X Ga _{0.47 + X} As and having a tensile stress, and In _{0.53 + X} Ga.
A semiconductor light-receiving element characterized by being formed by alternately laminating a large number of second strained superlattice layers formed of _0.47-X As and having a compressive stress. 2. A first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and a light absorption layer formed between the first semiconductor layer and the second semiconductor layer. In the semiconductor light receiving element, the light absorption layer includes a first strained superlattice layer formed of In _0.53-X Ga _{0.47 + X} As _Y P _1-Y and having a tensile stress, and In.
A semiconductor light receiving element characterized by being formed by alternately laminating a large number of second strained superlattice layers formed of _{0.53 + X} Ga _0.47-X As _Y P _1-Y and having a compressive stress.