JPH06120555A - Photodiode array - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a photodiode array capable of wavelength division without using a demultiplexer by providing a photodiode with wavelength selectivity. [Structure] n-type epitaxial layers 14 and 16 are provided as cladding layers above and below the multiple quantum well (MQW) light absorption layer 15, and the n-type epitaxial layer 14 has two P ⁺ layers.
Region 13 is formed. By applying different reverse bias voltages to the two p electrodes 11, the absorption peak wavelength of the photodiode can be matched with the wavelengths λ ₁ and λ ₂ of the optical signal, and wavelength division and detection can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to wavelength division multiplexing transmission (W.
DM), a parallel transmission system, or a photodiode array used in a field such as optical interconnection.

[0002]

2. Description of the Related Art A conventional technique for wavelength division multiplexing transmission (WDM transmission), which is one of the fields of application of the present invention, will be described.
FIG. 2 is a schematic configuration diagram for explaining the basic configuration of wavelength division multiplexing (WDM) transmission, which is a transmission mode in which a plurality of optical signals having different wavelengths are transmitted via one optical fiber. It In the figure, 20 is a signal input terminal, 21 is a transmitter, and 2
2 is a light emitting source, 23 is an optical multiplexer, 24 is an optical fiber transmission line, 25 is an optical demultiplexer, 26 is a light receiving element, 27 is a receiver,
28 is an output terminal of each channel. The input signals CH ₁ , CH ₂ , ..., CH _n in each channel drive the light emitting source 22 by the transmitter 21, but the wavelengths λ ₁ , λ ₂ ,.
Each _n is different. This is the optical multiplexer 23
Are combined with each other, combined into one optical fiber, and transmitted to the receiving side through the optical fiber transmission line 24. Optical demultiplexer 2 on the receiving side
Each wavelength lambda ₁ by 5, λ _2, ···, λ is demultiplexed into optical signals of _n, the output terminal 28 and demodulated by the receiver 27 into an electric signal by the light receiving element 26, respectively, of each channel The output signals CH ₁ , CH ₂ , ..., CH _n are taken out.

Thus, the WD that has been considered so far
In the M-transmission configuration, on the transmission side, optical signals from light sources with different wavelengths are combined into one optical fiber by an optical multiplexer, and on the reception side, optical signals of each wavelength are demultiplexed by an optical demultiplexer. The light receiving element converts this into an electric signal.

An example of a demultiplexer conventionally used as a demultiplexer in such wavelength division multiplexing transmission is shown in FIG.
Shown in (A) and (B). FIG. 3A shows a system using an interference film filter. The input light 30 having a plurality of different wavelengths receives the interference film filter 33 provided in the waveguide 34.
Thus, the wavelength components 31a, 31b, 31c, 31d are demultiplexed. 32 is a rod lens. In this example, the interference film filter uses a wavelength-selective reflective film formed by coating a dielectric multilayer film.

FIG. 3 (B) uses a diffraction grating,
The wavelength dispersion of the diffraction grating is used. The input light 30 is
The light is given from the optical fiber to the diffraction grating 35 via the rod lens or the waveguide 36, is demultiplexed as the output light 31 by the wavelength dispersion of the diffraction grating, and is extracted from each optical fiber. 37 is a spacer. In either case, the demultiplexed light is converted into an electric signal by the photodiode.

However, in the conventional configuration in which the individual optical components as described above are assembled, a fine optical adjustment is required when connecting the optical elements to each other. Due to fixing with adhesive etc., the production time is long,
The cost is high. There is a limit to reducing the size and weight of the receiver. There was such a problem.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and wavelength division can be performed without using a demultiplexer by providing a photodiode with wavelength selectivity. It is intended to provide a photodiode array.

[0008]

According to the present invention, in a photodiode array, a multiple quantum well layer, a cladding layer sandwiching the multiple quantum well layer from above and below, and a plurality of layers formed in one cladding layer are provided. It has a diffusion region and an electrode formed corresponding to the diffusion region.

[0009]

The multi-quantum well layer (MQW layer) will be described. A potential structure in which electrons and holes are confined in an extremely thin layer of 200 Å or less is called a quantum well, and a coupling force due to Coulomb force acts between confined electrons and holes. This electron-hole pair is called an exciton. In the quantum well structure, the binding energy of excitons is higher than that in the bulk, and the optical absorption line due to exciton absorption is clearly observed even at room temperature. When an electric field is applied to the quantum well structure semiconductor, the quantum well potential becomes asymmetric, the quantum level in the conduction band lowers, and the quantum level in the valence band increases. This effectively reduces the band gap, and therefore the absorption spectrum peak of excitons shifts to the low energy side, that is, the long wavelength side. This phenomenon is the so-called quantum confined Stark effect (QCSE).

A multiple quantum well layer (MQW layer) is formed with a barrier layer interposed in the quantum well layer. Multiple quantum well layer (M
Regarding the QW layer), when an electric field is applied perpendicularly to the quantum well layer, a so-called quantum confined Stark effect in which the exciton absorption spectrum shifts to the long wavelength side is observed as shown in FIG. An example of this is shown in FIGS.

FIG. 4 shows InGaAs as a quantum well layer,
A multi-quantum well layer is formed by using InP as a barrier layer and has a voltage of 0 due to the quantum confined Stark effect.
When a voltage is applied to the multiple quantum well layer for a wavelength longer than the peak wavelength of the absorption spectrum of V, that is, for light that is transmitted without being absorbed at a voltage of 0 V, the peak of the absorption spectrum shifts to the longer wavelength side. Therefore, the absorption coefficient for the light of the above wavelength is increased, and the wavelength selectivity can be changed.

FIG. 5 shows 100 Å thick AlGaInAs as a quantum well layer and 50 Å thick AlI as a barrier layer.
A multiple quantum well layer is constructed by using 30 pairs of nAs, and similarly, when a voltage is applied to the multiple quantum well layer due to the quantum confined Stark effect, the peak of the absorption spectrum shifts to the long wavelength side, and the wavelength selectivity Can be changed. As described above, the present invention utilizes the large optical absorption by the room temperature excitons and the shift of the optical absorption edge by the quantum confined Stark effect.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram of an embodiment of a photodiode array of the present invention. This embodiment is a case of two channels. In the figure, 11 is a p-side electrode, 12 is a surface protective film, 13 is a P ⁺ region, 14 is an n-type epitaxial layer, 15 is a multiple quantum well (MQW) light absorption layer, and 16 is n.
-Type epitaxial layer, 17 is an n-type semiconductor substrate, and 18 is n-type
The side electrode 19 is a multiple signal light.

An outline of the manufacturing process of this photodiode array will be described. First, on the n-type semiconductor substrate 17, the n-type epitaxial layer 14, the multiple quantum well (MQW) light absorbing layer 15, and the n-type epitaxial layer 16 are sequentially crystal-grown. In this embodiment, InP is used as the n-type semiconductor substrate 17, and the n-type epitaxial layers 14 and 1 are used.
InP was used for 6. The n-type epitaxial layer 14 is used as an upper clad layer, and the n-type epitaxial layer 16 is used as a lower clad layer. Multiple quantum well (M
In the QW) light absorption layer, InGaAs was used as the quantum well layer and InP was used as the barrier layer.

Next, the P ⁺ region 13 is formed in the n-type epitaxial layer 14 by the Zn selective diffusion method or the like. Since it has two channels, the P ⁺ region 13 is formed at two separate locations, and the photodiode regions of CH ₁ and CH ₂ are formed along the incident path of the multiplexed signal light. Then, in order to form the p-side electrode, mesa etching is performed, and the surface protective film 12 is formed thereon.

In order to apply a voltage to the multiple quantum well (MQW) light absorption layer 15, a contact hole is formed on the P ⁺ region 13 in the surface protective film 12 and the p-side electrode 11 is formed. The p-side electrode 11 is formed separately for each P ⁺ region. Further, an n electrode 18 is formed below the n type semiconductor substrate 17.

In the embodiment described above, the multiple quantum well layer (M
InGaAs / InP system was used as the QW layer) and InP was used as the n-type epitaxial layer.
sP / InP or AlGaInAs / AlInAs
Can also be used. For the n-type epitaxial layer, InP is used in the former case and AlI in the latter case.
nAs are used. These materials are for the long wavelength band, but can be applied to the short wavelength band by using the AlGaAs / GaAs system. In the case of this material,
AlGaAs is used for the n-type epitaxial layer and GaAs is used for the semiconductor substrate.

The operation will be described. As mentioned above,
Utilizing the quantum confined Stark effect (QCSE),
Reverse bias voltages V ₁ and V applied to the photodiodes of the respective channels constituted by the respective P ⁺ regions
By adjusting ₂ , the absorption peak wavelength of the photodiode of each channel is adjusted to the wavelengths λ ₁ and λ ₂ of the optical signal, as shown in FIG. Here, if λ ₂ > λ ₁ , the relation of the reverse bias voltage is | V ₂ |> | V ₁ |.

Two-wave (λ ₁ , λ ₂ ) multiplexed signal light 19 is
The light is made incident on the multiple quantum well light absorption layer 15 in the direction of the ridge waveguide. First, the light of wavelength λ ₁ is absorbed by the photodiode of channel 1 (CH ₁ ) and converted into photocurrent I _ph1 , and then the light of wavelength λ ₂ is absorbed by the photodiode of channel 2 (CH ₂ ). And converted into photocurrent I _ph λ ₂ .

In this way, the photodiode array shown in FIG. 1 has a demultiplexing function and a detecting function. In the case of n-wave multiplexed signal light, a photodiode array having n-channel photodiodes having the same structure as in FIG. 1 can be used.

Although the n-type substrate is used in the above embodiment, a p-type substrate can be used. In this case, an appropriate material may be selected for the multiple quantum well layer and the cladding layer.

[0022]

As is apparent from the above description, according to the present invention, the selected wavelength can be set by changing the voltage applied to each photodiode, and the demultiplexing and the detection of the optical signal can be performed in one. Since the photodiode array of the chip can be used, the size and weight can be reduced. Further, the structure is suitable for mass production, and there is an effect that the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a photodiode array of the present invention.

FIG. 2 is a schematic configuration diagram for explaining a basic configuration of wavelength division multiplexing transmission.

FIG. 3 is an explanatory diagram of a demultiplexer in wavelength division multiplexing transmission.

[Figure 4]

FIG. 5 is an explanatory view of the operation of the present invention.

FIG. 6 is an explanatory diagram of an operation of the embodiment of FIG.

[Explanation of symbols]

11 p-side electrode 12 surface protective film 13 P ⁺ region 14 n-type epitaxial layer 15 multiple quantum well (MQW) light absorption layer 16 n-type epitaxial layer 17 n-type semiconductor substrate 18 n-side electrode 19 multiple signal light

Claims (1)

[Claims] 1. A multiple quantum well layer, a cladding layer sandwiching the multiple quantum well layer from above and below, a plurality of diffusion regions formed in one of the cladding layers, and a plurality of diffusion regions formed corresponding to the diffusion regions. Photodiode array having patterned electrodes.