WO2018189898A1

WO2018189898A1 - Semiconductor light-receiving element

Info

Publication number: WO2018189898A1
Application number: PCT/JP2017/015362
Authority: WO
Inventors: 晴央山口; 亮太竹村
Original assignee: 三菱電機株式会社
Priority date: 2017-04-14
Filing date: 2017-04-14
Publication date: 2018-10-18

Abstract

The invention comprises: an InP substrate comprising InP; a buffer layer provided above the InP substrate, in contact or not in contact with the InP substrate; an electron multiplier layer provided above the buffer layer, in contact with the buffer layer, and formed from an Al-containing material; a photoabsorption layer provided above the electron multiplier layer, absorbing light to generate a carrier; and a contact layer provided above the photoabsorption layer. The invention is characterized in that the material of the buffer layer is a quaternary crystal having a lower Al composition than the electron multiplier layer.

Description

Semiconductor photo detector

The present invention relates to a semiconductor light receiving element used for optical communication, for example.

In order to realize long-distance transmission by optical communication, an avalanche photodiode (APD: Avalanche Photo Diode) having an action of amplifying an optical signal on the receiving side is indispensable. In the APD, as a layer for amplifying a received signal, a hole multiplication layer made of InP or an electron multiplication layer made of AlInAs is mainly used.

It is better to provide an electron multiplication layer made of AlInAs than a hole multiplication layer made of InP. Patent Document 1 discloses an avalanche photodiode having an excellent noise figure using an electron multiplier layer made of AlInAs.

Non-Patent Document 1 shows that AlInAs, which is a crystalline material with a high Al composition, has a higher thermal resistance than InP. Therefore, device characteristics may be deteriorated by local heat generated in the multiplication layer made of AlInAs.

Patent Document 2 discloses that in an avalanche photodiode having a hole multiplication layer made of InP, a buffer layer is inserted between a light absorption layer and a semiconductor substrate. However, in an avalanche photodiode having a hole multiplication layer, it is necessary to form a guard ring structure in the device in order to prevent local electric field concentration, and complicated manufacturing is required.

Japanese Patent No. 4166560 Japanese Patent No. 5433948

In a semiconductor light receiving element having an electron multiplier layer made of AlInAs, the thermal resistance of the electron multiplier layer and its vicinity is high, and the heat dissipation of the element may be insufficient. For example, it is conceivable to grow a buffer layer made of AlInAs on the InP substrate to suppress impurity diffusion from the substrate and improve crystal quality, and then grow an electron multiplication layer. In this case, since AlInAs, which is a material of the buffer layer, has a higher thermal resistance than InP, it is difficult for heat to escape during high-temperature operation of the element. Therefore, there is a problem that the heat dissipation of the element becomes insufficient.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a semiconductor light-receiving element that can improve heat dissipation while using an electron multiplying layer containing Al.

A semiconductor light receiving element according to the present invention is formed of an InP substrate, a buffer layer provided on the InP substrate, and a material including Al provided on the buffer layer in contact with the buffer layer. An electron multiplying layer; a light absorbing layer provided above the electron multiplying layer; and a contact layer provided above the light absorbing layer, wherein the material of the buffer layer is from the electron multiplying layer. Is a quaternary crystal having a low Al composition.

Other features of the present invention will be clarified below.

According to this invention, heat dissipation can be improved while using an electron multiplication layer containing Al by bringing a buffer layer having an Al composition lower than that of the electron multiplication layer into contact with the electron multiplication layer.

FIG. 3 is a cross-sectional view of the semiconductor light receiving element according to the first embodiment. It is a figure which shows the thermal analysis result of a semiconductor light receiving element. It is a figure which shows the relationship between the thickness of a buffer layer, and temperature. It is an energy band figure. It is an energy band figure. FIG. 6 is a cross-sectional view of a semiconductor light receiving element according to a second embodiment. It is an energy band figure.

A semiconductor light receiving element according to an embodiment of the present invention will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repeated description may be omitted.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view of a semiconductor light receiving element 10 according to the first embodiment. The semiconductor light receiving element 10 is an electron multiplying avalanche photodiode. The semiconductor light receiving element 10 includes an n-type InP substrate 12. A semiconductor light-receiving element can be formed by forming each layer on the InP substrate 12 by a method such as metal organic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE). it can.

Hereinafter, the structure of the semiconductor light receiving element 10 will be clarified while explaining the manufacturing method. First, the following layers are sequentially grown on the InP substrate 12 at a growth temperature of about 600 ° C. by the MOVPE method.
(1) The buffer layer 13 made of n-type AlGaInAs having a carrier concentration of 1 to 5 × 10 ¹⁸ cm ⁻³ and a thickness of 0.1 to 1 μm.
(2) An electron multiplying layer 14 having a thickness of 0.1 to 0.5 μm and made of i-type AlInAs.
(3) An electric field relaxation layer 15 made of p-type AlInAs having a carrier concentration of 0.5 to 1 × 10 ¹⁸ cm ⁻³ and a thickness of 0.05 to 0.15 μm.
(4)

Transition layers

16, 17, and 18 made of n ⁻ type AlGaInAs having a carrier concentration of 1 to 5 × 10 ¹⁵ cm ⁻³ , a thickness of 0.05 to 0.15 μm, and different compositions.
(5) The light absorption layer 19 made of n ⁻ -type InGaAs having a carrier concentration of 1 to 5 × 10 ¹⁵ cm ⁻³ and a thickness of 1 to 2 μm.
(6) The n ⁻ -type InP window layer 20 having a carrier concentration of 0.01 to 0.1 × 10 ¹⁵ cm ⁻³ and a thickness of 0.5 to 1 μm.
(7) The contact layer 21 made of p-type InGaAs having a carrier concentration of 1 to 5 × 10 ¹⁸ cm ⁻³ and a thickness of 0.1 to 0.5 μm.

By the crystal growth described above, the buffer layer 13 is provided on the InP substrate 12, and the electron multiplication layer 14 is provided on the buffer layer 13. Further, a light absorption layer 19 is provided above the electron multiplication layer 14, and a contact layer 21 is provided above the light absorption layer 19.

Next, for example, using a SiOx film having a circular opening with a diameter of 20 μm as a mask, Zn is diffused into the InP window layer 20 exposed from the mask to form the p-type conductive region 24. Next, a part of the contact layer 21 is removed by etching, whereby the contact layer 21 having a circular shape or a concentric circular shape in plan view is obtained on the p-type conductive region 24. The width of the contact layer 21 is 5 μm, for example.

Next, an antireflection film 23 made of SiNx is formed on the wafer. The antireflection film 23 also functions as a surface protective film. Thereafter, the antireflection film 23 on the contact layer 21 is removed.

Next, a p-electrode 22 is formed on the contact layer 21. The material of the p electrode 22 is, for example, AuZn. Next, the surface opposite to the surface on which the buffer layer 13 of the InP substrate 12 is laminated is polished to form the n-electrode 11. The material of the n electrode 11 is, for example, AuGeNi.

The operation of the semiconductor light receiving element 10 will be described. A reverse bias voltage is applied to the semiconductor light receiving element 10 from the outside so that the n electrode 11 side is at a positive potential and the p electrode 22 side is at a negative potential. In this state, light to be detected is incident on the p-type conductive region 24 from the p-electrode 22 side. When light in the near infrared region of the optical communication wavelength band of 1.3 μm band or 1.5 μm band is incident on the p-type conductive region 24, the light is absorbed in the light absorption layer 19 to generate electron-hole pairs. .

The generated electrons move toward the n electrode 11, and the generated holes move toward the p electrode 22. When the reverse bias voltage is sufficiently high, electrons are ionized in the electron multiplier layer 14 to generate new electron-hole pairs. Existing carriers and newly generated carriers cause further ionization, thereby causing avalanche multiplication in which electrons and holes multiply in an avalanche manner.

The electron multiplication layer 14 in which avalanche multiplication occurs is the most active region. Therefore, it is considered that the heat source during the operation of the semiconductor light receiving element 10 is centered on the electron multiplication layer 14. Since the electron multiplication layer 14 made of AlInAs contains a large amount of Al, the electron multiplication layer 14 has poor heat dissipation. Therefore, the buffer layer 13 made of AlGaInAs having a lower Al content than the electron multiplication layer 14 was brought into contact with the electron multiplication layer 14. By forming the buffer layer 13 between the InP substrate 12 and the electron multiplier layer 14 so as to be in contact with them, the thermal resistance around the electron multiplier layer 14 as a heat source can be lowered. Thereby, the heat dissipation within the element can be improved.

FIG. 2 is a diagram showing a thermal analysis result of the semiconductor light receiving element. Under the condition that the InP substrate 12 side is in contact with an ideal heat sink and becomes 0 [K], and the heat source is in the electron multiplication layer 14, the temperature of each layer is obtained from the heat sink as a reference by analytically solving the heat conduction equation. . On the left side, the temperature of the electron multiplying layer 14 when the buffer layer is formed of AlInAs having a thickness of 500 nm is shown. On the right side, the temperature of the electron multiplying layer 14 in the case where the buffer layer is formed of AlGaInAs having a film thickness of 500 nm and the composition adjusted so that the absorption short wavelength is 1.2 μm is shown.

FIG. 2 shows that when a buffer layer made of AlInAs is used, the temperature of the electron multiplying layer 14 is 337 K with respect to the heat sink. In addition, when a buffer layer made of AlGaInAs is used, it can be seen that the temperature of the electron multiplier layer 14 is 310 K with respect to the heat sink. Therefore, when AlGaInAs is used for the buffer layer, the temperature of the electron multiplier layer 14 can be lowered by about 8% compared to when AlInAs is used. This result is considered that AlGaInAs has an Al composition smaller than that of AlInAs and is caused by a decrease in the thermal resistance of the crystal near the electron multiplication layer.

FIG. 3 is a diagram showing the relationship between the thickness of the buffer layer 13 and the temperature. FIG. 3 shows the temperature difference between the InP substrate 12 and the electron multiplier layer 14 when the thickness of the buffer layer 13 of the semiconductor light receiving element 10 of the first embodiment is changed from 0.1 μm to 1.2 μm. . The thinner the buffer layer 13, the better the heat dissipation of the electron multiplying layer 14. When the crystal growth is actually performed, impurity diffusion occurs from the InP substrate 12 to the buffer layer 13, or the electric field distribution in the buffer layer 13 affects the operation of the electron multiplication layer 14. It is preferable to secure a thickness of 0.2 μm or more. On the other hand, when the buffer layer 13 is too thick, in addition to the deterioration of heat dissipation, the electron travel distance becomes long, so that the high-speed response of the semiconductor light receiving element is difficult. For this reason, the thickness of the buffer layer 13 is preferably 1.0 μm. Therefore, the layer thickness of the buffer layer 13 is preferably 0.2 μm or more and 1.0 μm or less.

FIG. 4 is an energy band diagram in the case where a buffer layer made of AlInAs is provided. FIG. 5 is an energy band diagram of the InP substrate 12, the buffer layer 13, and the electron multiplication layer 14 according to the first embodiment. As described above, the material of the buffer layer 13 is AlGaInAs. When the buffer layer 13 made of AlGaInAs is provided, not only the thermal resistance can be reduced, but also the band discontinuity between the InP substrate 12 and the electron multiplier layer 14 made of AlInAs can be reduced. Reduction of the band discontinuity contributes to speeding up the response.

In order to prevent light absorption by the buffer layer 13, it is important to set the composition of the buffer layer 13 so as not to be sensitive to the wavelength of incident light. By controlling the composition of Al, Ga, In, and As of the buffer layer 13, the absorption edge wavelength that is a wavelength corresponding to the band gap can be adjusted. Wavelengths shorter than the absorption edge wavelength are absorbed by the layer. The absorption edge wavelength λ (Eg) [μm] is equal to 1.24 / Eg. Here, Eg is the band gap energy [eV] of a certain layer.

The absorption edge wavelength of the buffer layer 13 is preferably 0.85 μm or more and 1.3 μm or less. Since the band gap energy of the electron multiplying layer 14 made of AlInAs is 1.45 eV, the absorption edge wavelength λ (Eg) of the electron multiplying layer 14 is 1.24 / Eg = 1.24 / 1.45. = 0.85 [μm]. Therefore, by setting the absorption edge wavelength of the buffer layer 13 to 0.85 μm or more, it is possible to prevent light absorbed by the electron multiplication layer 14 from being absorbed by the buffer layer 13. Further, when near infrared rays in the 1.3 μm band are incident on the semiconductor light receiving element 10, the near infrared rays are prevented from being absorbed by the buffer layer 13 by setting the absorption edge wavelength of the buffer layer 13 to 1.3 μm or less. it can.

In order to solve the problem that the semiconductor light-receiving element 10 according to the first exemplary embodiment of the present invention cannot secure sufficient heat dissipation with the electron multiplying layer 14 having a large amount of Al, the buffer layer 13 is brought into contact with the electron multiplying layer 14. Thus, the heat dissipation is improved. The semiconductor light receiving element 10 can be variously modified within a range not losing its characteristics.

For example, the material of the buffer layer 13 is not particularly limited as long as it is a quaternary crystal having an Al composition lower than that of the electron multiplication layer 14. For example, AlGaInAs or AlInAsP can be used as the material of the buffer layer 13.

The material of the electron multiplication layer 14 is not limited to AlInAs. For example, if the material of the electron multiplication layer 14 is AlGaInAs, the effect of lowering the thermal resistance of the electron multiplication layer 14 itself can be expected. The electron multiplying layer 14 is a semiconductor that is lattice-matched to the InP substrate 12 and has an electron ionization rate larger than the hole ionization rate, and any material containing Al can be employed. For example, AlInAs / AlGaInAs superlattice or InGaAsP may be used as the material of the electron multiplication layer 14.

In this embodiment, the case where the p-type conductive region 24 is formed by Zn diffusion has been described. However, an atom imparting another p-type conductivity may be used. As a Zn diffusion method, a solid phase diffusion method using ZnO or a Zn vapor phase diffusion method using a crystal growth furnace can be used. The contact layer 21 may be grown by crystal growth. In the present embodiment, the surface incident type structure in which light to be detected is incident on the p-type conductive region 24 from the p-electrode 22 side has been described. However, even if a back-illuminated structure in which light is incident from the InP substrate 12 side is employed, the above effect can be obtained.

The modifications mentioned in the first embodiment can be applied to semiconductor light receiving elements according to the following embodiments. Since the semiconductor light receiving element according to the following embodiment has many similarities to the first embodiment, differences from the first embodiment will be mainly described.

Embodiment 2. FIG.
FIG. 6 is a cross-sectional view of the semiconductor light receiving element according to the second embodiment. The buffer layer 13 of the semiconductor light receiving element of the second embodiment has a plurality of

layers

13a, 13b, 13c having different compositions. The

layers

13a, 13b, and 13c are formed of AlGaInAs but have different compositions.

FIG. 7 is an energy band diagram of the buffer layer 13 and the like according to the second embodiment. The plurality of

layers

13 a, 13 b, and 13 c have shorter absorption edge wavelengths as layers closer to the electron multiplication layer 14. In order to reduce the band discontinuity, it is desirable that the absorption edge wavelengths of the plurality of

layers

13 a, 13 b, and 13 c gradually become shorter from the InP substrate 12 toward the electron multiplication layer 14. When the buffer layer 13 is composed of a plurality of layers, the band gap may be changed continuously in the buffer layer 13 so that the portion where the band gap changes stepwise may be eliminated.

According to the semiconductor light receiving element according to the second embodiment, by providing the buffer layer 13 including the plurality of

layers

13a, 13b, and 13c having shorter absorption edge wavelengths as the layer closer to the electron multiplier layer 14, the InP substrate 12 is provided. And the band discontinuity between the electron multiplication layer 14 can be reduced. Therefore, the semiconductor light receiving element of the second embodiment is an element suitable for high-speed response.

As in the first embodiment, the composition of the buffer layer 13 is controlled so as not to be sensitive to the wavelength of incident light. Specifically, the composition ratio of AlGaInAs is adjusted. Further, the material of the buffer layer 13 need not be limited to AlGaInAs. The buffer layer 13 can be made of a material having a band gap between the band gap of AlInAs and the band gap of InP. For example, a layer formed of a combination of arbitrary materials among Al, Ga, In, As, and P can be used as the buffer layer.

Although the buffer layer 13 including the

layers

13a, 13b, and 13c has been described in the second embodiment, the number of the buffer layers 13 is not limited to three.

10 semiconductor light-receiving element, 12 InP substrate, 13 buffer layer, 14 electron multiplication layer, 19 light absorption layer, 21 contact layer

Claims

An InP substrate;
A buffer layer provided on the InP substrate;
An electron multiplying layer provided on the buffer layer in contact with the buffer layer and formed of a material containing Al;
A light absorption layer provided above the electron multiplication layer;
A contact layer provided above the light absorption layer,
The material of the buffer layer is a quaternary crystal having an Al composition lower than that of the electron multiplier layer.
2. The semiconductor light receiving element according to claim 1, wherein the material of the electron multiplying layer is AlInAs.
3. The semiconductor light receiving element according to claim 1, wherein the material of the buffer layer is AlGaInAs or AlInAsP.
4. The semiconductor light receiving element according to claim 3, wherein the absorption edge wavelength of the buffer layer is not less than 0.85 μm and not more than 1.3 μm.
5. The semiconductor light receiving element according to claim 1, wherein a thickness of the buffer layer is 0.2 μm or more and 1.0 μm or less.
The buffer layer has a plurality of layers having different compositions,
4. The semiconductor light receiving element according to claim 3, wherein the plurality of layers have shorter absorption edge wavelengths as a layer closer to the electron multiplication layer.
2. The semiconductor light receiving element according to claim 1, wherein the material of the electron multiplying layer is AlGaInAs.