JP2001308369A - Photodiode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photodiode, which has high sensitivity, can reduce its operating voltage and moreover, can respond at high speed. SOLUTION: A photodiode is provided with a plurality of semiconductor layers having light absorbing layers and distributed reflective layers to reflect the light transmitted through the light absorbing layers toward the light absrobing layers. The distributed reflective layers consist of a material which is not lattice-matching the semiconductor layers and respectively in contact with one semiconductor layer only of the plurality of the semiconductor layers through each surface in one side of their surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodiode having a distributed reflection layer for reflecting light transmitted through a light absorption layer.

[0002]

2. Description of the Related Art FIG. 3 is a cross-sectional view showing the structure of a conventional photodiode disclosed in Japanese Patent Application Laid-Open No. 61-2229371. The conventional photodiode shown in FIG.
^An n ⁺ -InP buffer layer, an n ^-- GaInAs light absorbing layer 3 and an n ^-- InP layer 5 are stacked on a ⁺ -InP semiconductor substrate 1 via a distributed reflector 19, and the n ^-- InP layer is formed. P-type conductive region 9 by diffusion or ion implantation in part of 5
Is formed. In the conventional photodiode, a guard ring 10 formed by, for example, diffusion or ion implantation of Be is formed around the p-conductive region 9 to alleviate the concentration of the electric field. The SiN anti-reflection coating film 7 is formed on the light-receiving portion of, and a p-electrode 17 is formed around the SiN anti-reflection coating film 7. The n electrode 18 is n
⁺ -Formed on the lower surface of the InP semiconductor substrate 1.

In the conventional photodiode configured as described above, the light to be detected 6 is incident on the photodiode via the anti-reflection coating film 7, and a part of the light to be detected is absorbed by light. The electrons absorbed in layer 3
It is converted into a hole pair, ie, a photocarrier. At this time, light transmitted through the light absorption layer 3 without being absorbed by the light absorption layer 3 reaches the distribution reflector 19. Here, the distribution reflector 19 is, for example, InP / GaIn so as to efficiently reflect incident light.
Part of the light is reflected by the distributed reflector 19, and is again incident on the light absorbing layer 3 and absorbed.

The holes generated in the light absorbing layer 3 are n ⁻
Avalanche multiplication in the high electric field region of the InP layer 5;
It is extracted as an external current with high gain. In the photodiode of FIG. 3, a current corresponding to the incident light is output and light is detected. The ratio (light absorptance) η of the light to be detected 6 absorbed by the light absorbing layer 3 is represented by the following equation, where W is the thickness of the light absorbing layer 3, α is the absorption coefficient, and R is the reflectance of the distributed reflector 19. It is given by equation (1).

Η = (1−Exp [−αW]) (1 + R Exp [−αW]) Equation (1)

According to equation (1), the wavelength λ of the light to be detected is
Is 1.55 μm and the absorption coefficient α is 6800 cm ⁻¹ , in order to obtain η = 0.9, the light absorption layer 3 needs a thickness W of about 3.4 μm when R = 0. , R =
At the time of 0.8, a thickness W of about 2.0 μm is required. As described above, the light absorption rate η in the light absorbing layer 3 can be increased by increasing the thickness W of the light absorbing layer 3 and the light receiving sensitivity can be increased. However, when the thickness W of the light absorbing layer 3 is increased, the light absorption rate η is increased. It is necessary to increase the voltage (operating voltage), and the high-speed response deteriorates. Therefore, in order to keep the applied voltage (operating voltage) low and to ensure high-speed response, it is necessary to reduce the thickness of the light absorption layer 3 and increase the light absorption rate η. It is necessary to increase the reflectance R in the layer 19.

The distributed reflection layer 19 is composed of a distributed reflector having a λ / 4 thick multi-periodic structure. Assuming that the refractive index is n ₁ , the refractive index of the high refractive index layer is n ₂ , and the refractive indexes of the layers located on the incident side and the passing side are n ₀ and n ₃ , respectively, are given by the following equation (2).

[0008] _{R = (n 0 n 2 p} -n 3 n 1 p) / (n 0 n 2 p + n 3 n 1 p) Equation (2)

The distributed reflector 19 is made of InP / GaInAsP.
, The refractive index of InP is 3.15 and InGa
Assuming that the refractive index of AsP is 3.43, 35 cycles are required to achieve R> 0.9, and the total thickness of the distributed reflector is 8.26 μm. In order to reduce this layer thickness, it is effective to use a periodic structure having a high refractive index difference,
Usable semiconductors are limited to those that can be lattice-matched. That is, since the refractive index of the semiconductor capable of lattice matching is in the range of 3 to 4, there is a limit to a periodic structure having a high refractive index difference, and no significant improvement can be expected.

Therefore, in the conventional photodiode, in order to reduce the operating voltage without decreasing the sensitivity of the photodiode and to realize a high-speed response,
By reducing the thickness of the light absorbing layer, the thickness of the light absorbing layer 3 is reduced by 5
It was necessary to provide a distribution reflector of twice the thickness.

[0011]

However, as in the prior art, the method of thinning the light absorbing layer and providing a distributed reflector having a thickness more than five times the thickness of the light absorbing layer 3 is as follows.
It takes a long time to grow, and furthermore, the strain increases as the thickness increases,
Defects and the like are likely to occur, and the crystal quality of the entire device is reduced, which has a problem of adversely affecting device characteristics. There is also a method in which a metal film is used as a reflection film. However, even with this method, a metal reflection film usually has a reflectance of only about 50 to 60%, so that there is a problem that the absorption layer cannot be made very thin. there were. Therefore, it has been difficult to reduce the operating voltage and increase the response speed without lowering the sensitivity.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a photodiode having high sensitivity, low operating voltage, and high-speed response.

[0013]

In order to achieve the above object, a photodiode according to the present invention comprises a plurality of semiconductors including a light absorbing layer and a light transmitted through the light absorbing layer. A distributed reflection layer for reflecting light toward the semiconductor, wherein the distributed reflection layer is made of a material that is not lattice-matched with the semiconductor and has only one semiconductor of the plurality of semiconductors on one surface. Is characterized by being in contact with. With this configuration, the distributed reflection layer can be formed by selecting various materials that are not lattice-matched with the semiconductor. Here, the distributed reflection layer is composed of two types or two types.
It may be configured using at least one kind of dielectric layer.

Further, in the photodiode of the present invention, the distributed reflection layer may be formed by alternately stacking first and second layers each having a different refractive index from each other and made of a dielectric material. Good.

In the photodiode according to the present invention, it is preferable that the distributed reflection layer is formed by alternately stacking ZnSe layers and MgF ₂ layers.

Further, in the photodiode of the present invention, the light absorption layer can be formed by epitaxial growth on a semiconductor substrate, and the distributed reflection layer can be formed by a method other than epitaxial growth.

Further, in the photodiode according to the present invention, the distributed reflection layer is formed on the upper surface of the semiconductor substrate via the plurality of semiconductor layers, and light is incident from the lower surface of the semiconductor substrate. Can be.

In the photodiode according to the present invention, the semiconductor layer including the light absorbing layer is formed on one surface of the semiconductor substrate, and the distributed reflection layer is formed on the other surface of the semiconductor substrate. You may comprise. In this case, it is preferable that the distributed reflection layer is formed in a concave portion formed by removing a part of the semiconductor substrate on the other surface of the semiconductor substrate.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A photodiode according to an embodiment of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. FIG. 1 is a sectional view showing a configuration of the semiconductor avalanche photodiode according to the first embodiment of the present invention. The photodiode according to the first embodiment is a back-illuminated flip-chip structure element that operates with respect to light in the 1.3 to 1.6 μm band incident from the back surface of the substrate, and has the following features. Have.

That is, in the semiconductor avalanche photodiode of the first embodiment, (1) the distributed reflector 8 is in contact with the p conductive region 9 on one surface, and the other surface of the distributed reflector 8 is in contact with the other semiconductor layer. By adopting a structure that can be formed so as not to contact, the distributed reflector 8 can be formed using a material that does not lattice match with the semiconductor layer such as the p conductive region 9 and by a method other than the epitaxial growth method. (2) By taking advantage of the first feature, the distributed reflector 8 is formed by alternately stacking a ZnSe layer and a MgF ₂ layer, which are materials that are not lattice-matched with the p conductive region 9 and the like. The second characteristic is that the distributed reflector 8 having a high reflectance is formed by forming the reflector.

More specifically, in the semiconductor avalanche photodiode according to the first embodiment, an n ⁺ -InP buffer layer is formed on (front surface) an n ⁺ -InP semiconductor substrate 1 having a SiN anti-reflection coating film 7 formed on the back surface. through 2 ⁿ - -GaInAs light absorbing layer _{3, Ga x in 1-x} As y P
Transition layer 4 composed of _1-y single layer or plural layers, n ⁻ −In
P layer 5 are sequentially stacked, the n ⁺ -InP buffer layer ^2, n - -GaInAs light absorbing layer 3, a transition layer 4 and the n ^- -
The layered portion composed of the InP layer 5 is separated into a photodetection section 20 and an n-electrode formation section 21.

The n ^--In in the photodetector 20 is
A p-type impurity is diffused or ion-implanted into a part of the P layer 5 to form a p-type conductive region 9, and a distributed reflector 8 is formed in the center of the p-type conductive region 9. P contact electrode 11 is formed so as to be in contact with conductive region 9. Incidentally, around the p conductive region 9,
A guard ring 10 formed by, for example, diffusing or ion-implanting Be to reduce the concentration of the electric field is formed. Further, a SiN film 14 having an opening so as to expose the surface of the p-conductive region 9 is formed in the light detection unit 20, and the distributed reflector 8 and the p-contact electrode 11 are connected to the p-conductive region 9 at the opening. It is formed so that it may contact. And
In the photodiode of the first embodiment, a bump electrode 13 made of, for example, AuSn is formed so as to cover the distributed reflector 8 and be electrically connected to the p-contact electrode 11.

In the photodiode of the first embodiment, the n-electrode forming portion 21 is made of, for example, AuGe so as to be in contact with the n ⁻ -GaInAs light absorbing layer 3, the transition layer 4 and the n ⁻ -InP layer 5. An n-contact electrode 12 is formed. Then, in the n-electrode forming portion 21, an SiN film 14 having an opening on the n-contact electrode 12 on the upper surface of the n-electrode forming portion 21 and continuous with the SiN film 14 of the photodetecting portion 20 is formed. The bump electrode 13 electrically connected to the n-contact electrode 12 is formed at the portion.

Here, in particular, in the first embodiment, as described above, the distributed reflector 8 is formed by alternately forming the ZnSe layer and the MgF ₂ layer so as to have a high reflectance for a desired wavelength. Thus, a distributed reflector having excellent reflection characteristics can be formed. Specifically, the refractive index of ZnSe is 2.46, and the refractive index of MgF ₂ is 1.38.
Since the refractive index difference is large, four periods and a layer thickness of 1.7
With a film having a thickness of 5 μm, a distributed reflector excellent in reflection characteristics with a reflectivity of 90% for light in the 1.3 to 1.6 μm band can be formed.

In the photodiode according to the first embodiment configured as described above, the light to be detected 6 enters through the SiN anti-reflection coating film 7, and a part of the light 6 enters the light absorption layer 3.
To generate electron-hole pairs, that is, photocarriers. The light transmitted through the light absorption layer 3 without being absorbed is reflected by the distributed reflector 8 having a high reflectance, and is again incident on the light absorption layer 3 to generate an electron-hole pair.

As described above, the photodiode according to the first embodiment is provided with the above-mentioned distributed reflector 8 having a high reflectivity. The same sensitivity is obtained. As described above, the sensitivity equivalent to that of the conventional example can be obtained by the light absorbing layer thinner than that of the conventional example, so that the operating voltage can be reduced and the high-speed response can be achieved while maintaining the required sensitivity.

In the photodiode of the first embodiment, the distributed reflector 8 is formed on the InP layer 5, but the present invention is not limited to this.
May be removed and formed on the removed portion. In this case, in order to remove the InP layer 5 with good controllability, it is also possible to provide an etching stopper layer made of a thin semiconductor layer, for example, a GaInAs etching stop layer, and use an etching solution that selectively dissolves the InP layer 5. it can.

In the first embodiment, the avalanche photodiode has been described. However, the present invention is not limited to this, and may be a pn or pin type photodiode, or may be another type of photodiode. The same operation and effect as in the first embodiment can be obtained. In the first embodiment, the avalanche photodiode in the 1.3 to 1.6 μm band has been described. However, the present invention may be applied to a photodiode of another wavelength band or a photodiode of another wavelength. The same function and effect as those of the first embodiment can be obtained.

Further, in the first embodiment, the distributed reflector 8 made of ZnSe and MgF ₂ is used. However, the present invention is not limited to this, and it may be configured using another dielectric. . The dielectric material that can be used as the material of the distributed reflector 8 in the present invention is a dielectric material that has low absorption in the wavelength band of light to be used and can increase the refractive index difference from the other material, and is preferable. Examples include, for example, SiO ₂ , SiN, and the like. Preferred combinations are (1) ZnSe and SiO ₂ , and (2) ZnSe.
And SiN, (3) MgF ₂ and SiO ₂ , and (4) MgF ₂ and SiN.

Embodiment 2 FIG. Next, a semiconductor avalanche photodiode according to a second embodiment of the present invention will be described with reference to FIG. Here, in FIG. 2, the components denoted by the same reference numerals as those in FIG. 1 are the same or corresponding components.

The semiconductor avalanche photodiode according to the second embodiment forms a light detecting portion by sequentially growing each semiconductor layer which needs to be formed by epitaxial growth on the upper surface of the InP substrate 1, and forms a light detecting portion on the opposite side of the light detecting portion. I
By forming the distributed reflector 8 on the lower surface of the nP substrate 1, the distributed reflector 8 can be formed using a material that does not lattice match with the semiconductor layer and by a method other than the epitaxial growth method. And still,
In the photodiode of the second embodiment, taking advantage of the characteristics, the distributed reflector 8 is formed by alternately laminating a ZnSe layer and a MgF ₂ layer, which are materials that are not lattice-matched with the p conductive region 9 and the like. Thus, the distributed reflector 8 having a high reflectance is formed.

[0032] In detail, the semiconductor avalanche photodiode embodiment 2, ⁿ via the n ⁺ -InP n ⁺ -InP buffer layer 2 on the upper surface of the semiconductor substrate 1 - -GaInAs light absorbing layer 3, Ga _x In _1-x As _y P
Transition layer 4 composed of _1-y single layer or plural layers, n ⁻ −In
The P layer 5 is sequentially stacked, and a p-type impurity is diffused or ion-implanted into a part of the n ⁻ -InP layer 5 to form a p-conductive region 9, thereby forming a photoelectric conversion portion. Here, the p-contact electrode 17 is formed on the periphery of the p-conductive region 9 via the p ⁺ -GaInAs contact layer 16. Also, n ⁻ −I including the surface of p conductive region 9
On the surface of the nP layer 5, a SiN anti-reflection film 7 is formed.
An electrode pad 15 electrically connected to the p-contact electrode 17 is formed between the N anti-reflection film 7 and the p-contact electrode 17. Around the p-conductive region 9, a guard ring 10 formed by diffusing or ion-implanting Be, for example, to reduce the concentration of the electric field is formed.

In the photodiode according to the second embodiment, a recess 30 is formed in a portion of the lower surface of the n ⁺ -InP semiconductor substrate 1 facing the p conductive region 9, and ZnSe and ZnSe are formed in the recess 30 as in the first embodiment. A distributed reflector 8 made of MgF2 is formed. Further, an n-contact electrode 18 is formed outside the concave portion 30 on the lower surface of the n ⁺ -InP semiconductor substrate 1.

The photodiode according to the second embodiment configured as described above includes the distributed reflector 8 having a high reflectance similarly to the first embodiment, and therefore has the same operation and effect as the first embodiment. Having. Therefore, Embodiment 2
In the photodiode, the same sensitivity as that of the conventional example can be obtained by the light absorbing layer 3 which is thinner than the photodiode of the conventional example, so that the operating voltage can be reduced while maintaining the required sensitivity, and high-speed response can be achieved.

In the second embodiment, the avalanche photodiode has been described. However, the present invention is not limited to this, and the same operation and effect as those of the second embodiment can be obtained even with a pn or pin type photodiode. . Also,
In the first embodiment, the avalanche photodiode in the 1.3 to 1.6 μm band has been described, but the present invention is not limited to the photodiode having the wavelength.

In the first embodiment, the distributed reflector 8 made of ZnSe and MgF ₂ is used. However, the present invention is not limited to this, and other dielectrics may be used as in the first embodiment. You may comprise using it.

As described above, each of the photodiodes of Embodiments 1 and 2 has a structure in which it is not necessary to epitaxially grow a semiconductor layer on the reflection distributor 8.
For example, the reflection distributor 8 can be formed using a thin film forming apparatus other than the epitaxial growth apparatus such as a sputtering apparatus. Thereby, various semiconductors or dielectrics can be used as the material of the distributed reflector 8, and a distributed reflector having a high reflectance can be formed.

[0038]

As described above in detail, the photodiode according to the present invention is made of a material that does not lattice match with the above-mentioned semiconductor, and has one surface in contact with only one of the plurality of semiconductors. Since the distributed reflection layer is provided, various materials suitable for the reflection layer can be selected to form a distributed reflection layer having a high reflectance. As a result, sensitivity equivalent to that of the conventional example can be obtained with a light absorbing layer thinner than that of the conventional example, so that it is possible to provide a photodiode having high sensitivity, low operating voltage, and high response speed. Further, the photodiode according to the present invention can be manufactured at a high yield because the semiconductor layer can be prevented from growing on the distributed reflection film, so that the quality of the semiconductor crystal such as the light absorption layer can be improved. And high quality can be obtained.

In the photodiode of the present invention, the distributed reflection layers have different refractive indices and are alternately laminated with first and second layers made of a dielectric material. A high distributed reflection film can be formed. Therefore, the operating voltage can be further reduced and the response speed can be further increased.

Further, in the photodiode according to the present invention, by forming the distributed reflection layer by alternately stacking ZnSe layers and MgF ₂ layers, a distributed reflection film having a higher reflectance can be formed. Therefore, the operating voltage can be further reduced and the response speed can be further increased.

Further, in the photodiode of the present invention, the light absorption layer can be formed by epitaxial growth on a semiconductor substrate, and the distributed reflection layer can be formed by a method other than epitaxial growth. A photodiode which can form a reflective film and can be manufactured at low cost can be provided.

Further, in the photodiode according to the present invention, the distributed reflection layer is formed on the upper surface of the semiconductor substrate via the plurality of semiconductor layers, and light is incident from the lower surface of the semiconductor substrate. Can be.

In the photodiode according to the present invention, the semiconductor layer including the light absorbing layer is formed on one surface of the semiconductor substrate, and the distributed reflection layer is formed on the other surface of the semiconductor substrate. Alternatively, light can be incident from the semiconductor layer side.

In the case where light is incident from the side of the semiconductor layer, the distributed reflection layer is formed in a concave portion formed by removing a part of the other surface of the semiconductor substrate, thereby absorbing light. Since the layer and the reflective layer can be brought close to each other, light can be efficiently reflected.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a photodiode according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a photodiode according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional photodiode.

[Explanation of symbols]

1 n ⁺ -InP semiconductor substrate, 2 n ⁺ -InP buffer layer, 3 n ^-- GaInAs light absorption layer, 4 Ga _x In
_{1-x As y P 1-} y single layer or plural layers than it made the transition layer, 5
InP layer, 6 light to be detected, 7 non-reflective coating film of SiN, 8 distributed reflection layer, 9 p conductive region by diffusion or ion implantation, 10 guard ring, 11, 17
p contact electrode, 12, 18 n contact electrode, 1
3 bump electrode, 14 SiN protective film, 15 electrode pad, 16 p ⁺ -GaInAs contact layer.

Claims (7)

[Claims] 1. A photodiode comprising: a plurality of semiconductors including a light absorption layer; and a distributed reflection layer configured to reflect light transmitted through the light absorption layer toward the light absorption layer. Is a photodiode made of a material that does not lattice match with the semiconductor, and is in contact with only one of the plurality of semiconductors on one surface. 2. The photodiode according to claim 1, wherein said distributed reflection layer has a refractive index different from each other and a first layer and a second layer each made of a dielectric are alternately laminated. 3. The distributed reflection layer comprises a ZnSe layer and a MgF
_{2. The} photodiode according to claim 1, wherein _two layers are alternately stacked. 4. The method according to claim 1, wherein the light absorption layer is formed by epitaxial growth on a semiconductor substrate, and the distributed reflection layer is formed by a method other than epitaxial growth. Photodiode. 5. The distributed reflection layer is formed on an upper surface of a semiconductor substrate via the plurality of semiconductor layers, and allows light to enter from a lower surface of the semiconductor substrate.
A photodiode according to the item. 6. The semiconductor layer according to claim 1, wherein the semiconductor layer including the light absorbing layer is formed on one surface of the semiconductor substrate, and the distributed reflection layer is formed on the other surface of the semiconductor substrate. A photodiode according to any one of the preceding claims. 7. The photodiode according to claim 6, wherein the distributed reflection layer is provided in a recess formed by removing a part of the semiconductor substrate on the other surface of the semiconductor substrate.