JPH02228079A - Pin photodiode - Google Patents

Abstract

PURPOSE:To contrive the extending of frequency zone and the reduction in contact resistance of the electrode by making the are of an intrinsic layer virtually equal to the light receptive diameter. CONSTITUTION:This PIN photodiode is provided with an n-type InP substrate 1 and an n-type InP layer 2 as an n-type semiconductor layer, an n<->-type InGaAs layer 3 as an intrinsic semiconductor layer, and a p-type InP layer 4 as a p-type InP layer, which are laminated. On said p-type InP layer 4, an electrode 5 is placed which defines a window for transmitting an incident light(IL). At this time, a junction diameter (d) defined by the n<->-type InGaAs layer 3 and a light receptive diameter (d') defined by the electrode 5 are processed into approximately equal sizes. Also, the area where the electrode can be attached is made wider because the only intrinsic layer is etched while leaving the above layer. Thus, the frequency zone can be extended and also the contact resistance can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to fields where high-speed response to optical signals is required;
Especially used for optical communication, optical signal processing, or optical measurement. The present invention relates to a p-type semiconductor, an intrinsic
ic) The present invention relates to a light receiving element having a three-layer structure of a semiconductor layer and an n-type semiconductor layer, that is, a PIN photodiode, and more specifically relates to improving the frequency band of a PIN photodiode.

In this specification, "intrinsic semiconductor" does not necessarily mean an intrinsic semiconductor, but refers to a semiconductor with a low carrier concentration. The intrinsic semiconductor layer in the PIN photodiode actually exhibits p-type or p-type conductivity characteristics, absorbs light, and efficiently generates electron-hole pairs.

〔overview〕

The present invention expands the frequency band of the PIN photodiode and reduces the contact resistance of its electrodes by making the area of the intrinsic layer substantially equal to the light-receiving diameter in the PIN photodiode.

[Conventional technology]

FIGS. 5 to 7 show cross-sectional structures of different types of conventional PIN photodiodes. These structures are: (a) Wuang et al., 188B) Transactions;
On Electron Devices, Volume εD-34, Page 938, 1987 (S, Y, Wang et,
al, , IEE [E Trans.

electron Dev, 80-34. p, 9
38.1987), et al., Miura et al., 1
Volume 5, page 1371, 1987 (SlMiura
et, al,, IEEE J, L+ghtwa
veTechno1. , LT-5, p, 1371.1
987) (C) Bowers et al., Electronics
Letters, Volume 21, Page 812, 1985 (J,
E. Bowers et al.

F, Iectron, Lett, 21. p.81
2.1985), respectively.

In the conventional example shown in FIG. 5, an n-type 1
The nP layer 2, the n-type 1nGaAs layer 3, and the p-type nP layer 4 are epitaxially grown, and electrodes 5.6 are formed on the surface of the p-type layer nP layer 4 and the back surface of the n-type 1nP substrate 1, respectively. A part of the InP layer 2, the n-type 1nGaAs layer 3, and the p-type InP layer 4 are etched into a mesa shape.

The n-type 1nGaAS layer 3 is used as an intrinsic layer and absorbs light incident from the p-type nP layer 4 side to generate electron-hole pairs. These electrons and holes drift to the n-type 1nP layer 2, the p-type layer, and the nP layer 4, respectively, and are each taken out as an electric signal from the electrode 6.5.

In the conventional example shown in FIG. 6, an n-type 1
The nP layer 2, the n-type 1nGaAs layer 3, and the InP cap layer 7 are epitaxially grown, and the InP cap layer 7 is
A p-type InP region 4' is formed by diffusing 2n into the p-type 1nP region 4', and an electrode 5 and an antireflection film 8 are provided on the surface of the p-type 1nP region 4'. An electrode 6 is provided on the back surface of the n-type 1nP substrate 1 .

In the conventional example shown in FIG. 7, a mesa structure is formed similarly to the example shown in FIG. 5, and then the back surface of the n-type 1nP substrate 1 is processed to provide an entrance window. Electrode 5' is p-type InP
Cover the entire surface of layer 4.

[Problem that the invention seeks to solve]

However, in the conventional example shown in FIG. 5 or 6, since the upper electrode blocks the incident light, there is a portion in the junction region that does not contribute to the generation of electron-hole pairs. Therefore, there is a drawback that the apparent junction capacitance increases and the frequency band of the PIN photodiode is limited.

The conventional example shown in FIG. 7 solves this drawback and makes the light-receiving diameter and the junction diameter coincide. However, this conventional example
This had the disadvantage of complicating the manufacturing process because back surface processing was required. Moreover, since light is incident from the n-type layer, there is a drawback that the response speed is slightly reduced.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a PIN photodiode in which the light-receiving diameter and the junction diameter substantially match each other through a simple manufacturing process.

[Means for solving problems]

The PIN photodiode of the present invention is characterized in that the intrinsic semiconductor layer is processed to have a shape in a direction perpendicular to incident light that is substantially equal to the window defined by the upper electrode.

Selective etching is used to perform such processing.

When InGaAs is used as the intrinsic layer, to selectively etch only this layer, a sulfuric acid solution, that is, an aqueous solution of H2SO and H20□, is used.

As a result, the InGaA
The diameter of the s layer can be made to match the light receiving diameter.

In this specification, "upper" and "lower" do not refer to a specific direction of the element, but refer to a direction away from the substrate and a direction toward it, respectively.

[For production]

Since the light-receiving diameter and the junction diameter are almost the same, the junction capacitance can be reduced and the frequency band can be expanded compared to a conventional element having the same light-receiving diameter. Furthermore, since only the intrinsic layer is etched leaving the upper layer, the area on which electrodes can be attached becomes larger. When the electrode area is increased, the series resistance component of the element can be reduced.

〔Example〕

FIG. 1 shows a cross-sectional structure of a PIN photodiode according to an embodiment of the present invention.

This PIN photodiode uses n as an n-type semiconductor layer.
It includes a 1nP type substrate 1 and an n-type 1nP layer 2, an n-type 1nGaAs layer 3 as an intrinsic semiconductor layer, a p-type nP layer 4 as a p-type semiconductor layer, and these layers are stacked. . An electrode 5 is provided on the p-type layer nP layer 4, and this electrode 5 defines a window through which incident light passes.

Here, the feature of this embodiment is that n-type InGa
The As layer 3 has a window shape (electrode 5) in the direction perpendicular to the incident light.
The reason is that it is processed into a shape that is substantially the same as the inner shape of the That is, the junction diameter d defined by the n-type InGaAs layer 3 and the light receiving diameter d' defined by the electrode 5.
are almost equal.

FIG. 2 shows a method of manufacturing this PIN photodiode.

First, an n-type 1nP layer 2, an n-type 1nGaAs layer 3, and a p-type nP layer 4 are epitaxially grown on an n-type 1nP substrate 1, and the surface of the p-type InP layer 4 and the back surface of the n-type 1nP substrate 1 are , respectively form ohmic electrodes 5.6.

As a result, the structure shown in FIG. 2(a) is obtained.

Next, KKI-121 (HCl: CH2C0OH:
H2O2 = 1:2:1) or bromomethanol (n
A part of type 1nP layer 2, n-type InGaAs layer 3 and p
The mold layer nP layer 4 is etched into a mesa shape. As a result, a structure as shown in FIG. 2(b), that is, a light receiving element equivalent to that shown in FIG. 5 is obtained.

Furthermore, the n-type 1nG'aAs layer 3 is selectively etched using sulfuric acid peroxide (H2S04+H2O2+H20). As a result, the light receiving element shown in FIG. 2(C) is obtained.

FIG. 3 shows the etching rate of sulfuric acid peroxide for InG'aAs and InP. InP requires a longer time for etching than InG'aAs, and this can be used to perform selective etching.

The frequency band of a PIN photodiode depends on carrier transit time in the intrinsic layer and a time constant determined by the product of junction capacitance and load impedance. In this example, there is no part of the n-type 1nGaAS layer 3 where light is blocked by the electrode 5, and the entire region contributes to quantum efficiency. Therefore, no unnecessary junction capacitance occurs.

This will be explained in comparison with the conventional example shown in FIG.

When a voltage is applied to the electrode 5.6, most of the electric field is n-
Type 1 is added to the nGaAs layer 3. Therefore, the junction capacitance is determined by the dimensions of the n-type 1nGaAs layer 3. Here, assuming that the n-type 1 nGaAs layer 3 is completely depleted, its junction capacitance C is C=ε,ε. π(d/
2)''/L, where C1 is the dielectric constant, ε is the dielectric constant in vacuum, d is the junction diameter, and L is the thickness of the n-type 1nGaAs layer 3.

Here, the light receiving diameter is set to 25 threshold. In the case of this embodiment, the light receiving diameter d'ζ junction diameter dζφ25μ0. In contrast, in the conventional example, even for the same light receiving diameter, the width of the electrode 5 is 10 μm and the process margin is 5 μm. Therefore, joint diameter = φ (25 + (10 + 5) x 2) μ0 = φ
It becomes 55 μm. If the thickness of the n-type 1nGaAs layer 3 is the same, the junction capacitance is proportional to the junction area. Therefore, the ratio between the junction capacitance C1 of the embodiment and the junction capacitance C2 of the conventional example is c, : c2= (25/2)" : (55
/2)2''=,1:4.84.In other words, the junction capacitance is 1/2'' compared to the conventional example.
It is reduced to about 4.84.

FIG. 4 shows calculated values of the frequency band with respect to the film thickness of the n-type 1nGaAs layer 3.

This calculation is based on the junction capacitance described above, as described by Bowers et al.
, B.Bowers et al., , IεBE
J.Lightwave technology.

The method described in T-5, p. 1339.1987) was used. The equivalent circuit at this time is also shown in FIG. In addition to the calculated values for the embodiment, FIG. 4 shows the calculated values for the conventional example shown in FIG. 5 as conventional example I, and the calculated values for the conventional example shown in FIG. 7 as conventional example ■. show.

When the n-type 1nGaAs layer 3 is made thinner, the transit time of carriers is shortened, so that the band tends to be widened.

However, making the device thinner increases the junction capacitance of the device and narrows the band. In Conventional Example I, the junction capacitance is affected even where the film thickness is relatively thick. In addition, in the case of n-type incidence (backside incidence) shown in conventional example (■), although it has the same junction capacitance as the embodiment example, the band is slightly narrower because the hole saturation speed is slower than the electron speed. It gets narrower.

In the above embodiments, a PIN photodiode using InP/InGaAs/InP has been described as an example, but the present invention can be similarly implemented with a PIN photodiode having other structures. For example, A4GaAs/GaAs/A1GaAs
In the case of a PIN photodiode using a PIN photodiode, the GaAs intrinsic layer can be selectively etched by using ammonia hydrogen peroxide (NH,OH: H20□=1:20), and the present invention can be implemented in the same manner. Selective etching of GaAs is described in detail in, for example, Electronic Materials, May 1974 issue, page 86.

〔Effect of the invention〕

As explained above, the PIN photodiode of the present invention can expand the frequency band with the same light-receiving diameter, and has the effect of enabling the detection of rapidly changing optical signals and optical signals modulated at high frequencies. be.

Furthermore, since the electrode area can be increased, contact resistance can be reduced, and the resistance component in series with the PIN photodiode can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional structural diagram of a PIN photodiode according to an embodiment of the present invention. FIG. 2 is a diagram showing the manufacturing method. FIG. 3 is a diagram showing the etching rate of sulfuric acid water flow for InGaAs and InP. FIG. 4 is a diagram showing calculated values of the frequency band with respect to the film thickness of the n-type 1nGaAs layer. FIG. 5 is a cross-sectional structural diagram of a first conventional PIN photodiode. FIG. 6 is a cross-sectional structural diagram of a second conventional PIN photodiode. FIG. 7 is a cross-sectional structural diagram of a third conventional PIN photodiode. l ・n-type InP substrate, 2 ・n-type InP layer, 3-n-
type InGaAs layer, 4.p-type layer nP layer, 4'.p-type 1nP region, 5.5', 6...electrode, 7...InP
Cap layer, 8... antireflection film. Patent Applicant Optical Measurement Technology Development Co., Ltd. Agent Patent Attorney Nao Ide Takashi Fugyo Case Shoulder 1st IR Sho Aot Irisho 2nd Time Exploration 1 Imashi 7° Yu Tatsuma 0 3 Figure iM 1 ■m) fan

Claims (1)

[Claims] 1. An n-type semiconductor layer, an intrinsic semiconductor layer, and a p-type semiconductor layer.
In the PIN photodiode, the p-type semiconductor layer is stacked with a window through which incident light passes, and the intrinsic semiconductor layer has a shape in a direction perpendicular to the incident light that is similar to the window. A PIN photodiode characterized in that it is processed into a shape substantially equal to that of the PIN photodiode.