JPH03201571A - Wavelength multiple photodetector - Google Patents

Abstract

PURPOSE:To suppress a leakage current and to reduce a junction capacity by providing one conductivity type short wavelength light absorption layer and one conductivity type long wavelength light absorption layer on the upper and lower sides of a substrate, and forming an opposite conductivity type layer formed by impurity diffusion on the opposite side surface of the short and long wavelength layers to the substrate. CONSTITUTION:One conductivity type short wavelength light absorption layer 2 and one conductivity type long wavelength light absorption layer 5 are respectively provided on upper and lower sides of a substrate 1. Further, opposite conductivity type layers 3, 7 are formed by impurity diffusion on the surface of the layers 2, 5 opposite to the substrate 1. Accordingly, PN junction area of an optical diode can be reduced. Further, in a wavelength multiple receiver formed integrally, a mesa shape of a step can be eliminated at the PN junction formed by impurity diffusion. Therefore, a leakage current can be prevented.

Description

[Detailed Description of the Invention] (Table of Contents) Industrial Field of Application Prior Art (Fig. 5) Problems to be Solved by the Invention Examples of Means and Actions for Solving the Problems (a) First Example of the Invention Description of the embodiment (FIGS. 1 and 2) (b) Description of the second embodiment of the present invention (FIGS. 3 and 2) (c) Description of the third embodiment of the present invention (FIG. 2) (Fig. 4, Fig. 2) Effects of the invention [Summary] Regarding a wavelength multiplexed light receiving device that enables wavelength multiplexed communication, the present invention aims to suppress leakage current and reduce junction capacitance. A light absorbing layer and a long wavelength light absorbing layer of one conductivity type are provided on the upper and lower sides of the substrate, and a surface of the short wavelength light absorbing layer and the long wavelength light absorbing layer opposite to the substrate is provided with impurity diffusion. The method includes forming layers of opposite conductivity type.

[Industrial application field]

The present invention relates to a wavelength multiplexed light receiving device that enables wavelength multiplexed communication.

(Prior Art) When performing optical communication, a device has been proposed that transmits a plurality of optical signals having different wavelengths in a layered manner and converts the signals into electrical signals for each wavelength using a light receiving element.

This device separates a wavelength-multiplexed optical signal into single-wavelength optical signals using a demultiplexer made of prisms, filters, etc., and converts each wavelength into an electrical signal using separate light-receiving elements.

However, this configuration requires a large number of parts, so
This impedes miniaturization of the wavelength multiplexed light receiving device.

Therefore, as a light-receiving device that does not use a demultiplexer, as shown in Fig. 5 (a
), an N-type InGaAsP layer 51 that absorbs short wavelength light is provided on the upper layer of the P9-type TnPM 50, while
Below that is an N-type InGaAs layer 5 that absorbs long wavelength light.
2, a first photodiode D consisting of P1 type TnPw450 and N type InGaAsP layer 51 is obtained.
, P′″ type InP layer 50 and N type InGaAs layer 52
A device has been proposed in which a second photodiode Dt is integrally formed to form a circuit as shown in FIG. 5(b).

According to this device, two wavelengths λ1. By irradiating an optical signal overlapping λ2 from above, the optical signal λ1 with a short wavelength is
is converted into an electrical signal by the first photodiode D, while the optical signal λ2 having a longer wavelength is converted by the second photodiode D,
This makes it possible to convert wavelength multiplexed light receiving devices into smaller sizes.

[Problem to be solved by the invention]

By the way, when forming this device, N+ type InP
On the a-plate 53, an N-type 1nP buffer layer 54, a long-wavelength light absorption layer 52 made of N-type rnGaAs, and a P0-type Tn
P layer 50, short wavelength light absorption 1 made of N-type 1nGaAsP
51 and a cap layer 55 made of N1 type TnP are formed in this order.

Further, the sides of the short wavelength light absorbing Ji 51 and the cap layer 55 are etched by photolithography or the like to form a mesa shape.

and first and second photodiodes D,,D.

An anode common electrode A is formed on the top of the P'' type 1nP layer 50, and a cathode electrode CI of the first photodiode D is provided on the upper periphery of the cap ji155, and
The cathode electrode C2 of the second photodiode D2 is connected to the substrate 53.
It is designed to be formed on the bottom surface of the .

Therefore, the first photodiode D1 formed in a mesa shape
There is a problem that a leakage current flows through the stepped portion B, or that the junction capacitance due to the PN junction surface of the second photodiode D2, which is formed widely, becomes large.

The present invention has been made in view of these problems, and an object of the present invention is to provide a wavelength multiplexed light receiving device that can suppress leakage current and reduce junction capacitance.

(Means for Solving the Li! Problem) The above-mentioned problem is solved by forming a short-wavelength light absorption layer 2 of a conductive type and a long-wavelength light absorption layer 5 of one conductivity type on a substrate 1, as illustrated in FIG. In addition to being provided on the upper and lower sides, an opposite conductivity type r*3.7 is formed by impurity diffusion on the surface of the short wavelength light absorption layer 2 and the long wavelength light absorption layer 5 on the side opposite to the substrate 1. This problem can be solved by using a wavelength multiplexed light receiving device.

[For production]

According to the present invention, the - conductivity type short wavelength light absorption N2 and the one conductivity type long wavelength light absorption N5 are provided on the upper and lower sides of the substrate l, and among the short wavelength light absorption N2 and long wavelength light absorption N5, the substrate Since the opposite conductivity type N3.7 was formed on the surface opposite to 1 by impurity diffusion, the P of the photodiode
The N junction area can be reduced.

Furthermore, in the integrally formed wavelength multiplexing light receiving device, since the stepped mesa shape can be eliminated from the PN junction surface formed by impurity diffusion, the generation of leakage current can be prevented.

(Example) Therefore, an example of the present invention will be described below based on the drawings.

(a) Description of the first embodiment of the present invention Fig. 1 is a block diagram of a device showing an embodiment of the present invention, in which reference numeral 1 is an N-type 1nP substrate, on which , N
A mesa-shaped short wavelength light absorption N2 made of 1nP type is formed with a thickness of 4 μm, and in the center of this short wavelength light absorption N2, a P layer with a depth of 0.2 μm formed by P and Zn diffusion is formed.
A type diffusion N3 is provided, and when light with a wavelength of 0.8 μm is irradiated onto the P9 type diffusion 3, it absorbs the light and excites electrons, creating a photocurrent between it and the InP substrate 1. It is structured to flow.

Further, under the InP substrate l, there are each a buffer WA4 made of N-type 1nP, a long-wavelength light absorption layer 5 made of N-type 1nGaAs, and a cap layer 6 made of N-type 1nP.
A P" type diffusion layer 7 is formed at the center of the cap layer 6 to reach the bottom of the long wavelength light absorption layer 5 by diffusion of P and Zn. The configuration is such that a photocurrent flows between the P0 type diffusion 7 and the InP substrate 1 when light with a wavelength of 1.55 μm passes through the short wavelength light absorption layer 2 and is irradiated onto the long wavelength light absorption layer 5. has been done.

Here, each of the N-type layers N2.4 to N7 is formed by an epitaxial growth method, and silicon, sulfur, etc. are used as impurities to make the N-type layer. 10"/cd or more, short wavelength light absorption N2 is 1 g+s to 10"/cd, buffer layer 4 is 1015 to 10"/cd, long wavelength light absorption layer 5 is 10"/cd.
”/eta, cap layer 6 is 101S to 10”/
cd, the two P″″ type diffusion layers 3 are 3×lO eyes/d
becomes.

8 is St, N formed to have a film thickness of about 3000.

This passivation film 8 is a passivation film consisting of the surface of the short wavelength light absorption layer 2 and the short wavelength light absorption layer N2.
Openings 9.10 are provided on the upper surface of the InP substrate 1 where no P'' type diffusion layer 3 is present, and on the lower surface of the cap layer 6, and at positions where the P'' type diffusion layer 3 is to be formed.
P through 10.

It is configured to diffuse Zn in ampules.

Furthermore, among the passivation B8, InP substrate 1
An opening 11 is formed in the upper surface area, and a cathode common electrode 12 made of gold-germanium-nickel alloy/gold is formed in this opening 11.

Reference numeral 13 denotes an anti-reflection film made of Si3N formed on the surface of the central region of the upper P1 type diffused layer 3. Around this anti-reflection film 13, there is a first layer connected to the P type diffusion layer 3. An anode electrode 14 is formed.

Note that reference numeral I5 in the figure indicates an opening 10 on the lower surface of the cap layer 6.
The second anode electrode 16 made of titanium/platinum/gold connected to the cap layer indicates a chip bonding band made of titanium/platinum/gold provided on the passivation film on the lower surface of the cap layer.

Next, the operation of the above embodiment will be explained.

In the above-mentioned embodiment, P is placed above the InP substrate 1.

The layers up to type diffusion N3 form the first photodiode D, while the layers P below from the InP substrate 1.

The second photodiode I)t is formed by the layers up to the type diffusion layer 7.
t, and these constitute an electronic circuit as shown in FIG. 2(a).

In this circuit, the positive pole of the power source W is connected to the cathode common electrode 12, and the first and second photodiodes DIl,
A negative pole is connected to the D-th anode electrode 14.15, and a reverse bias voltage is applied to the two photodiodes DIl and the D-th photodiode.

From this state, when optical signals with two wavelengths of 0.8 μm and 1.55 pm are irradiated through the antireflection film 13, the first
In the photodiode D11, since 0.8 μm light is absorbed by the short wavelength light absorption layer 2, a photocurrent flows due to the photoelectric effect, and the current It in the bias application direction increases.

On the other hand, light with a wavelength of 1.55 μm passes through the short wavelength light absorption layer 2 and reaches the long wavelength light absorption layer 15, where it is absorbed. A corresponding photocurrent flows, and the current (2) in the bias direction increases.

The reason for this phenomenon is that the InP forming the short wavelength light absorption layer 2 has a band gap such that electrons are excited from the valence band to the conduction band by receiving light with a wavelength of 0.8 μm. This is because the bandgap size of the InGaAs layer constituting the long wavelength light absorption layer 5 is such that when exposed to a wavelength of 1.55 μm, electrons are excited from the valence band and transferred to the conduction band. This is because they are designed to move.

(b) Description of the second embodiment of the present invention In the first embodiment described above, the short wavelength light absorption layer 2 was formed of N-type 1nP, thereby absorbing light with a wavelength of 0.8 μm. However, when trying to operate the first photodiode with light having a wavelength of 1.3 μm, the third
Make the structure as shown in the figure.

That is, in FIG. 3, the reference numeral 20 in the figure is an N3 type 1nP
A 1 μm thick film made of N-type TnP formed on the substrate 1
This buffer layer 20 is formed in a mesa shape, and on top of this is a buffer layer of N type! A short wavelength light absorption layer 21 made of nGaAsP with a thickness of 4 μm and a cap N22 made of N type 1nP with a thickness of 11 Im are formed. The P1 type diffusion 23 that reaches the InP substrate 1 is formed by P and Zn diffusion, and is configured such that a current flows between the P0 type diffusion 23 and the InP substrate l by irradiating light with a wavelength of 1.3 μm. There is.

Here, to give an example of the impurity concentration, the InP substrate l is I
X 10”/c4 or more, buffer layer 20 is 10+s~
l O”/cd, short wavelength light absorption layer 21 is 10”/cj
.

Cap N22 is 10"-10"/cd, P" type diffusion I!23 is 3X10"/cd.

Reference numeral 24 denotes a passivation film made of Si3N4 formed to a thickness of about 3000 Å, and this passivation film 24 includes a buffer N20 above the InP substrate l, a short wavelength light absorbing layer N21. It covers the cap M22 and is formed on the upper surface of the InP substrate l where these layers 20 to 22 are not present, and an opening 25 is provided at the position where the upper P" type diffusion 71J23 is formed. It is configured to diffuse P and Zn in ampules through the openings 25.

Furthermore, an opening 26 is formed in the upper surface of the TnP substrate in the passivation film 24, and this opening 26 has the following characteristics:
A cathode common electrode 27 made of gold-germanium-nickel alloy/gold is formed.

Reference numeral 28 denotes an anti-reflection film with a thickness of 1900 Å made of Si3N4 formed on the surface of the central region of the upper P-type scattering layer 23. Around this anti-reflection film 28, a P-type diffusion layer 111
A first anode electrode 29 connected to 23 is formed.

Further, under the InP substrate l, as in the first embodiment, a buffer layer 4 and a long wavelength light absorbing layer J! ! ! J5, cap layer 6
, a P'' type scattered layer 7 is formed, and a second anode electrode 15 connected to the lower P'' type scattered layer 7 is connected to the opening lO of the passivation film 8 on the lower surface of the cap layer 6.
A passivation film pad 16 is formed thereon.

This embodiment device has an electronic circuit similar to that of the first embodiment (FIG. 2(a)), and each layer 20 to 23 formed on the InP substrate 1 constitutes a first photodiode Dlt. become.

In this case, when light with a wavelength of 1.3 μm is irradiated through the antireflection film 28, short wavelength light is absorbed! 1!121 causes a photocurrent to flow through the first photodiode D.

Here, the N type that constitutes the short wavelength light absorption 1121! nGa
The bandgap of AsP is such that upon receiving light with a wavelength of 1.3 μm, electrons in the valence band are excited to be excited in the conduction band.

(c) Description of the third embodiment of the present invention In the second embodiment, an electrode 2 formed on an InP substrate 1 is used.
7 to two photodiodes D11. ．． Although the cathode common electrode of DI2 was used, there is an apparatus shown in FIG. 4 that separately forms the cathode electrodes of two photodiodes.

That is, a semi-insulating InP substrate 30 with a resistance value of 10'Ωcm
A buffer M31 made of N1nP is formed on the buffer layer 31, and a mesa-shaped N-type 1nGaA layer is formed on the buffer layer 31.
A short-wavelength light absorbing layer N32 made of sP and a cap FJ33 made of N-type inP are formed, and a P scattering layer 1934 reaching the top of the short-wavelength light absorbing layer 32 is formed in the central region of this cap layer 33.

Further, a buffer layer 35 made of N-type InP is formed under the semi-insulating 1nP substrate 30.
A mesa-shaped long-wavelength light absorption layer 36 made of N-type 1nGaAs and a cap layer 37 made of N-type 1nP are formed below, and the central region of this cap layer 37 reaches the bottom of the long-wavelength light absorption layer 36. A P9 expanded P11 layer 38 is formed.

Then, these are covered with a passivation layer [39] made of Si3N, and a window 40 is formed in the upper part of the P dispersion layer 4, and an anti-reflection film 4 made of 5L3N4 is formed here.
Form 1.

Further, a first anode electrode 42 is provided on the side of the antireflection film 41.
and a second anode electrode 44 is formed in the window 43 provided in the passivation 11939 of the lower P'' diffusion 1538 region.
Made of titanium/platinum/gold.

Furthermore, openings 45.46 are formed in the passivation film 39 on the surfaces of the two buffs 553135, and through these openings 45.46, the first and second cathode electrodes 47.
48 is connected to the buffer layer 31.35.

According to this, as shown in FIG. 2(c), an upper cathode electrode 47 for controlling the first photodiode D,
The lower cathode electrode 48 constituting the second photodiode D is formed separately.

In the three embodiments described above, a P° type scattered layer was formed using an N type substrate, but it is also possible to use the opposite conductivity type.

[Effects of the Invention] As described above, according to the present invention, a - conductivity type short wavelength light absorption layer and a single conductivity type long wavelength light absorption layer are provided on the upper and lower sides of the substrate, and the short wavelength light absorption layer A layer of opposite conductivity type is formed by impurity diffusion on the surface of the long-wavelength light absorption layer opposite to the substrate, so that the PN of the photodiode is
The bonding area can be reduced.

Furthermore, in the integrally formed wavelength multiplexing light receiving device, the PN junction surface formed by impurity diffusion can eliminate the stepped mesa shape, making it possible to prevent leakage current from occurring.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a device showing a first embodiment of the present invention, FIG. 2 is a circuit diagram of a device showing first to third embodiments of the present invention, and FIG. 3 is a cross-sectional view of a device showing a first embodiment of the present invention. FIG. 4 is a cross-sectional view of a device showing a third embodiment of the present invention; FIG. 5 is a cross-sectional view and circuit diagram showing an example of a conventional device. . (Explanation of symbols) 1...N゛ type 1nP base layer, 2...Short wavelength light absorption layer, 3.7...P'' type scattering layer 4...Buffer layer, 5... - Long wavelength light absorption layer, 6... Cap layer, 20... Buffer layer, 21... Short wavelength light absorption layer, 22... Cap layer, 23... P° type scattering layer 30 ...InP substrate, 31.35...Buffer layer, 32...Short wavelength light absorption layer, 36...Long wavelength light absorption layer, 33.37...Cap layer, 34. 38...P'' type scattered layer Applicant: Fujitsu Co., Ltd.

Claims (1)

[Claims] A short wavelength light absorption layer of one conductivity type and a long wavelength light absorption layer of one conductivity type are provided on the upper and lower sides of the substrate, and one of the short wavelength light absorption layer and the long wavelength light absorption layer is provided on the side opposite to the substrate. 1. A wavelength multiplexed light receiving device characterized in that a layer of opposite conductivity type is formed on a surface by diffusion of impurities.