JPH02246268A - Photoreceptor - Google Patents

Abstract

PURPOSE:To equalize the incident light intensity entering from photowaveguide layers to PIN photodiodes by a method wherein N layers are tapered in the light emitting direction along the photowaveguides. CONSTITUTION:The title photodetector is provided with photowaveguides 12, 14 leading light as well as PIN photodiodes 20, 30 composed of N layers 21, 31 formed on the photowaveguides 12, 14, I layers 22, 32 formed on the N layers 21, 31 and P layers 23, 33 formed on the I layers 22, 32. At this time, the N layers 21, 31 are formed to be tapered in the direction from one ends of the photowaveguides 12b, 14b to the other ends. Through thee procedures, the unevenness in the incident light intensity can be compensated, thereby enabling even incident light to be entered.

Description

[Detailed Description of the Invention] [Summary] Regarding a light receiving device, particularly a light receiving device in which an optical waveguide and a PIN photodiode are integrally formed, it is possible to remove the PI from the optical waveguide layer.
The purpose of the present invention is to provide a light receiving device that uniformizes the intensity of light incident on an N photodiode, and includes an optical waveguide that guides light, an N layer formed on the optical waveguide, and an a PIN photodiode having one layer and a P layer formed on the first layer, the thickness of the N layer being formed such that it gradually becomes thinner along the direction of propagation of light in the optical waveguide. Configure it to do so.

[Industrial Application Field] The present invention relates to a light receiving device, and particularly to a light receiving device in which an optical waveguide and a PIN photodiode are integrally formed.

Optical communication systems are gradually entering the practical stage because they are capable of high-speed, large-capacity communication. Current optical communication systems use a method that transmits the strength and weakness of light as information, but the next generation optical communication method is a coherent optical transmission method that transmits information by adding information to the frequency, phase, amplitude, etc. of light. Attention has been paid.

[Prior Art] In a light receiving device using a coherent optical transmission system, detection is performed by forming a beat between a phase modulated optical signal and a reference optical signal. Therefore, the light receiving device needs to have a function of combining the modulated optical signal and the reference optical signal. Conventionally, there has been a problem in that the optical coupling section and the light receiving section are formed independently, which increases noise generation and signal attenuation.

For this reason, the optical coupling part and the light receiving part are integrated into OBI C (
Opto-Electronic Interarate
dC1rcuit) is being considered. The conditions necessary to integrate the optical coupling part and the light receiving part are: ■ High quantum efficiency, ■ High speed operation, ■ PI
It is necessary to increase the current generated in the N photodiode to reduce noise. From the condition (2), it is necessary to increase the power of the optical signal that enters the PIN photodiode as much as possible. It is necessary to downsize the diode to reduce its capacitance, and from the condition (2), it is necessary to improve the coupling between the optical waveguide and the PIN photodiode.

Taking these conditions into consideration, a light receiving device has been proposed in which an optical waveguide and a PIN photodiode are integrally formed as shown in FIG. 4(a).

An n-InP buffer layer 52 on a high-resistance InP substrate 50
An optical waveguide layer 54 of n-InGaAsP is formed therebetween. A PIN photodiode 56 is formed on the optical waveguide layer 54 and is elongated along the light traveling direction. That is, 800 nm of n”InP is formed on the optical waveguide layer
Layer 57, one layer of n-InGaAs 58, two layers of p''InP
Layers 59 are stacked in sequence. Although the entire PIN photodiode 56 is small and has a small capacity, the optical waveguide layer 5
There is an advantage that the contact area between the 4th and 8th layers 57 is large and a large amount of incident light can be obtained.

[Problem to be solved by the invention] However, in the case of the above-mentioned proposed light receiving device, the PI
There is a problem in that the intensity of light incident on the N photodiode exhibits non-uniformity in that it gradually decreases along the traveling direction of the light, as shown in FIG. 4(b). therefore,
More carriers are generated on the left side of the PIN photodiode shown in FIG. 4(a), and fewer carriers are generated on the right side.

High light intensity (If too many carriers are generated in the PIN photodiode, high-speed operation will be impaired due to the space charge effect caused by the carriers, so there is a limit to the light intensity that can be incident on the PIN photodiode. If the light intensity is non-uniform as shown in FIG. 4(b), the light intensity that can enter the PIN photodiode is limited by the limit value of the strongest part on the left side. Due to the non-uniformity of light intensity shown in (b),
There is a problem in that the limit of light intensity that can be incident on the PIN photodiode is lowered.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a light receiving device in which the intensity of light incident on a PIN photodiode from a leading waveguide layer is made uniform.

[Means for Solving the Problems] The above purpose is to provide an optical waveguide for guiding light and 1. A PIN photodiode including an N layer formed on the optical waveguide, one layer formed on the N layer, and a P layer formed on the one layer, the thickness of the N layer being This is achieved by a light receiving device characterized in that the optical waveguide is formed so as to become gradually thinner along the direction in which light travels.

[Function] According to the present invention, since the thickness of the N layer is formed so as to gradually become thinner along the direction from the one end to the other end of the optical waveguide layer, non-uniformity of incident light intensity can be avoided. can be compensated for and uniform light can be incident.

[Example] A light receiving device according to an example of the present invention will be described with reference to FIGS. 1 and 2. Figure 1 is a perspective view showing the entire light receiving device;
FIG. 2(a) is a cross-sectional view taken along the line IIa--IIa of the main part of the light receiving device, and FIG. 2(b) is a cross-sectional view taken along the line mb-mb.

As shown in FIG. 1, two optical waveguides 12 and 14 are formed on a high resistance InP substrate 10.

These optical waveguides 12 and 14 are optical coupling parts 1 for optical detection.
The modulated optical signal is inputted to one side, and the reflex optical signal is inputted to the other side. A PIN photodiode 20.30 is formed at each end of the optical waveguide 12.14.

The optical waveguide 12.14 is composed of n-InP buffer layers 12a, 14a formed on the InP substrate 10, and n-InGaAsP optical waveguide layers 12b, 14b formed on the buffer layers 12a, 14a. There is.

Details of PIN photodiode 20.30 Part 1
This will be explained with reference to the drawings and FIG.

The PIN photodiode 20 is formed on the optical waveguide layer 12b via an etching stop layer 12c of n''InGaAs.The etching stop layer 12c was inserted as required in the manufacturing process, and its details will be described later. This will be explained later.

Eight layers 21 of n''InP are formed on the n''InGaAs layer 12c, and the feature of this embodiment is that the thickness of these eight layers 21 is such that the thickness of the eight layers 21 is equal to This point is gradually becoming thinner. That is, the non-uniformity of light intensity that the conventional light receiving device had is compensated for by changing the thickness of the eight layers 21.

It is desirable that the thickness of the thinnest part of the eight layers 21 corresponds to the thickness of the conventional eight layers, and the other parts are made into a rectangular shape that is thicker than that.

On the eight layers 21, one layer 22 of n'''InGaAs and two layers 23 of p''InP are laminated in order, as in the conventional case.

On the second layer 23, a P-side electrode 24 of AuZnAu is formed. AuS is placed on the 8 layers 21 extending on the InP substrate 10.
N-side type of n [! 25 is formed.

The PIN photodiode 30 also has the same configuration as the PIN photodiode 20, and has an n"InGaAs layer 14.
N layer 31 of n”InP and 1 layer 3 of nInGaAs on c
Two layers 33 of 2 and p”InP are laminated in order, and the two layers 33
A P-side electrode 34 is formed on the top, and an N-side electrode 35 is formed on the eight layers 31 extending on the I-nP substrate 10 .

Note that an n-InP buried cladding layer (not shown) is formed on the optical waveguide 12.14 where the PIN photodiode 20.30 is not formed.

Optical waveguide 12.14 and PIN photodiode 20.
30 is entirely covered with a protective film 40 of silicon nitride film.

In this way, according to this example, the light intensity was made uniform by changing the thickness of the eight layers of the PIN photodiode, so the limit of light intensity that can be incident on the PIN photodiode was increased, and high speed with low noise was achieved. It is possible to make it work.

Next, a method for manufacturing the light receiving device will be explained using FIG.

Figures 3(al) to (gl) are I[a-1] of Figure 2(a).
Corresponds to the cross-sectional view taken along the line 1a, and is shown in Fig. 3 (a2) to (o2)j.
, corresponds to the left half of the cross-sectional view taken along the line mb-nb in FIG. 2(b).

First, an n-InP buffer layer 12a and n-In*Ga+-gAa are formed on the entire surface of a high-resistance InP substrate 10.

P, -2 optical waveguide layer 12b and a thickness of 50A n” In
An etching stop layer 12c of GkAs is sequentially formed by MOCVD (FIGS. 3(a) and 3(a2)).

Note that there is a relationship between the In composition ratio X and the As composition ratio y as shown in the following equation.

y=0.42/(0,18+0.02x) Next, the buffer layer 12a, the optical waveguide layer 12b, and the etching stop layer 12c are etched and shaped into the shape shown in FIG. 1 to form the optical waveguide 12. (Fig. 3 (bl), (b)
2)), .

Next, while controlling the thickness, eight layers 21 of n''TnP are formed on the entire surface so as to have the tapered shape shown in the figure (Fig. 3 (cl), (c2)).
It is formed by a liquid phase growth method using a solution in which P is supersaturated in 1 liter. Therefore, the thickness of the n''InP layer is controlled by controlling the time of immersion in the solution, that is, the time of liquid phase growth.

Subsequently, one layer 22 of n-InGaAs and p“In
Two layers 23 of P are formed on the entire surface (Fig. 3 (cl), (
c2)).

Next, using the planar resist layer (not shown) of the PIN photodiode 20 as a mask, p''I
The two nP layers 23 are removed by etching (Fig. 3 (dl)).
(d2)) Since the etching solution HCj selectively etches only InP, etching stops at one layer 22 of n-InGaAs.

Next, using the etched two layers 23 of p''InP as a mask, one layer 22 of n-InGaAs is removed by etching with a mixed etching solution of HF and HNOs (
As shown in FIGS. 3(el) and (e2), since the etching solution, a mixture of HF and HNOs, selectively etches only InGaAs, the etching stops at the 8 layers 21 of n''InP.

Next, using a resist layer (not shown) formed to cover the region where the N-side electrode 25 is to be formed as a mask, the 8 layers 21 of n''InP are etched away using an HCj etching solution (FIG. 3 (fl)). , (f2)).

At this time, etching is performed on the etching stop layer 1 of n''I nGaAs formed under the 8 layers 21 of n''InP.
2c and does not reach the optical waveguide layer 12b. In other words, the etching stop layer 12c is n"In
This is to prevent the optical waveguide layer 12b from being etched when the P 8 layer 21 is etched.

Next, after removing the etching stop layer 12c in areas other than the PIN photodiode 20 area, a silicon oxide film (not shown) is covered only on the PIN photodiode 20 to form an n-InP buried cladding layer 42. Next, the silicon oxide film is peeled off and the protective film 4 of the silicon nitride film is removed.
form 0.

Subsequently, the portion of the 8 layer 21 extending to the InP substrate 10 and the 2
A contact hole is formed in the protective film 40 on the layer 23, and an N-side electrode 25 and a P-side electrode 24 are formed respectively (third
Figure (Ql), (lJ2)).

The present invention is not limited to the above embodiments, and can be modified in various ways.
For example, the materials constituting the substrate, optical waveguide, and PIN photodiode are not limited to those of the above embodiments.

[Effects of the Invention] As described above, according to the present invention, the light intensity incident on the PIN photodiode is made uniform, which increases the limit of the light intensity that can be incident on the PIN photodiode. The device can be realized.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a light receiving device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the main parts of the light receiving device, FIG. 3 is a process diagram of a method for manufacturing the same light receiving device, and FIG. 4 is a conventional method. FIG. 2 is a sectional view of the main parts of the light receiving device. In the figure, 10... InP substrate 12.14... Optical waveguides 12a, 14a... Buffer layer (n-InP) 12b
, 14b... Optical waveguide layer (n-InGaAsP) 12c, 14c... Etching stop layer (n"I
nGaAs) 16... Optical coupling section 20.30... PIN photodiode 21.31
・N layer (n"1nP) 22.32-I layer (n""InGaAs) 23.33
・P layer (p"InP) 24.34...pm electrode 25.35...N side electrode 40...protective film 42...buried cladding layer (n-1nP) 50...
InP substrate 52... Buffer layer (n-InP) 54... Optical waveguide layer (n-InGaAsP) 56... PIN photodiode 57 - N layer (n''InP) 58 - I layer (n-InGaAs) 59-P layer (p” InP)

Claims (1)

[Claims] An optical waveguide that guides light, an N layer formed on the optical waveguide, an I layer formed on the N layer, and a P layer formed on the I layer. PIN photodiode, the thickness of the N layer is
A light receiving device characterized in that the optical waveguide is formed so as to become gradually thinner along the direction in which light travels.