JPH05218462A - Semiconductor photodetective device - Google Patents

Abstract

PURPOSE:To prevent signals from being distorted and to dispense with an expensive lens so as to lessen a semiconductor photodetective device in manufacturing cost by a method wherein a disused carrier trapping structure is provided to a photodiode chip, and signal light emitted from an optical fiber is made to impinge on the photodiode chip without interposing a lens optical system. CONSTITUTION:A photodiode chip 1 is provided with a structure which treats a photocurrent, which is generated by light that impinges on a region outside a PN junction which serves as a photodetective region, as ineffective, and an optical fiber 6 is made to approach the photodiode chip 1 so as to make it as high in sensitivity as required without interposing a lens optical system between them. The optical fiber 6 is inserted into a housing 8 through a ferrule 7, and the light emitting end face of the optical fiber 6 and the light receiving face of the photodiode 1 are made to confront each other without interposing an optical lens or the like between them. An expensive lens need not be used, and furthermore an optical fiber is not required to be finely aligned with a lens, so that a photodetective device of this design can be obtained at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving device used in a receiving device of an optical communication system.

[0002]

2. Description of the Related Art In a semiconductor light receiving device for optical communication using an optical fiber, a photodiode chip 1 is mounted on a header 2 and leads 3 are provided as shown in FIG.
The optical signal is converted into an electric signal by taking out a photocurrent to the outside through. The cap 4 has a translucent window 5 and is used for hermetically sealing the photodiode chip. Here, the ferrule 7 in the housing 8
A condenser lens 9 is used to efficiently irradiate the photodiode chip 1 with the light from the optical fiber 6 that is inserted through. The shape shown in FIG. 3 is called a coaxial type.

The apparatus shown in FIG. 4 is of a butterfly type, and has a short housing 8. Basically, the function is the same as that of FIG.
A C (integrated circuit) chip or the like may be arranged so that the photocurrent signal from the photodiode chip 1 is amplified to some extent and then taken out to the outside.

[0004]

A conventional device of this type uses a single mode fiber or a multimode fiber as an optical fiber. For example, in the 1.3 μm band light, the core diameter is about 10 μm for a single mode fiber and about 50 μ for a multimode fiber.
m. The light emitted from the end face of the optical fiber spreads into the space at an angle according to the refractive index difference between the core and the clad of the optical fiber. Therefore, the lens 9 is used to efficiently collect the expanding light on the light receiving surface of the photodiode. Especially when using a photodiode chip with a small light receiving diameter of 100 μm or less for high speed,
It is often the case that an aspherical lens or a SELFOC lens having better light condensing characteristics is used, and there is no choice but to use expensive parts.

Even if these lenses are used, very high accuracy is required for alignment with the optical fiber. Particularly, when the portion B shown in FIG. 3 is fixed, a positional accuracy of about ± 15 μm is required to keep the sensitivity variation within ± 0.5 dB. For fixing this kind of parts,
Spot welding with a YAG laser is most often used, but it still causes misalignment and yield is as low as 70-80%. Further, it takes a long time of 20 to 30 minutes for one alignment.

A particular problem is that the condensed light beam hits the outside of the light receiving region of the pn junction of the photodiode chip. This is shown in FIG. In the fat diode chip 1, an epitaxial growth layer 12 is formed on a semiconductor substrate 11, and a diffusion region 13 having a polarity opposite to that of the layer 12 is formed by diffusion of a metal element. Layer 1
The boundary portion between 2 and the region 13 is called a pn junction, and the light applied to this portion mainly contributes to the photocurrent. The photocurrent is taken out as a signal to the outside through the electrodes 14 and 15.

Here, reference numeral 16 is a core 6 of the optical fiber 6.
It shows the spread of the light beam emitted from ′.
The light absorbed in the region 13 and its immediate vicinity (for example, 3 to 5 μm) of this beam contributes to the photocurrent at high speed and efficiently by the electric field applied to the pn junction, but outside the region, the electric field is increased. Is not applied, the absorbed light will generate a photocurrent with a very slow response speed. Then, in the reproduction of analog signal light,
The signal becomes out of phase, the distortion level becomes high, and there is a problem that noise appears in the reproduced image. Further, in the reproduction of the digital signal light, the pulse waveform is distorted (particularly, the falling portion of the rectangular pulse has a μsec tail), which causes a problem that high-speed communication cannot be performed. In order to prevent such an adverse effect, the light from the optical fiber is focused on the photodiode chip by a high-grade and expensive optical system.

Although the semiconductor light receiving device is indispensable for optical communication, its difficulty and high price hinder the rapid spread of the optical communication system.
An object of the present invention is to solve such a problem.

[0009]

The present invention has an integrated structure in which a housing having an optical fiber inserted therein is fixed to a header on which a photodiode chip is mounted, and the light receiving surface of the photodiode chip is an optical fiber. In the semiconductor light receiving device arranged so as to face the emitting end face, the photodiode chip has a pn junction region for outputting a photocurrent as a detection signal on the light receiving face, and carriers generated around the pn junction region are generated. It is characterized in that it has a region to be captured, and the light emitted from the optical fiber is immediately incident on the light receiving surface without passing through the lens optical system.

[0010]

According to the structure of the present invention, since the photodiode chip is provided with the carrier trapping structure to be invalidated, the signal light from the optical fiber is transmitted to the photodiode chip without interposing the lens optical system. Even if it is incident,
No signal distortion will occur.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a side view of the semiconductor light receiving device showing a crushed section of the main part, and FIG. 2 is an enlarged view of the main part. As shown in the figure, the point different from the prior art is that the photodiode chip 1 has a structure (a charge trapping photodiode chip The optical fiber 6 is brought close to the photodiode chip 1 without using a lens optical system to obtain a desired sensitivity.

As shown in FIG. 1, a header 2 is mounted with a photodiode chip 1, and a housing 8 is integrated with the photodiode chip 1. The optical fiber 6 is inserted into the housing 8 by the ferrule 7, and the light emitting end face of the optical fiber 6 and the light receiving face of the photodiode chip 1 face each other without an optical lens or the like.

As such a photodiode chip 1 that can be used in the semiconductor light receiving device according to the embodiment of the present invention, the photocurrent generated by the light incident on the outside of the pn junction, which is the light receiving region, is invalidated. (Charge trap type photodiode chip) having
FIG. 2 shows an example thereof. In this structure, a region 17 having the same polarity as the region 13 is formed in the epitaxial layer 12 by thermal diffusion of a metal element. The photocarriers generated in the region 17 do not flow toward the region 13 and disappear in the vicinity of the pn junction between the epitaxial layer 12 and the region 17 or at the pn junction exposed on the chip end face thereof. Specifically, Japanese Patent Application No. 2-308094 by the applicant,
The details are given in No. 2-230207.

When such an improved photodiode chip is used, even if the light beam is spread, it does not affect the characteristics at all, so it is not necessary to use an expensive lens and the optical fiber is finely aligned. Is no longer necessary, and a semiconductor light receiving device of low cost can be obtained very easily.

In the configuration of FIG. 1, a long wavelength band (1.1 μm-
An example of a semiconductor light receiving device used for optical communication of 1.6 μm) will be described. As the photodiode chip 1, I
nP is used as the substrate and Z is used as the InGaAs epitaxial layer.
A charge trap type photodiode chip in which a pn junction having a light receiving region of 100 μm is formed by n diffusion and a charge trap region is further formed by the same method is used. Of course, in this chip 1, an antireflection film is formed on the entire surface of the light receiving portion and the charge trapping region and the passivation of the junction portion by the SiN film. This chip 1 is bonded to the Kovar header 2 using AuSn,
Electrical continuity with the lead 3 is established with a μm gold wire.

Next, in order to prevent the returning light, the end face is
Fix the single mode fiber 6 cut diagonally to the ferrule 7 and attach it to the stainless steel housing 8
Prepare the one fixed on. At this time, the fixed position of the ferrule 7 is fixed to a value calculated by using geometrical optics according to the light receiving area of the chip 1 and the distance between the light receiving surface of the photodiode chip 1 and the tip of the fiber 6.

Next, the chip 1 is irradiated with a laser beam of 1.3 μm from the optical fiber 6, and while monitoring the photocurrent,
Using a YAG laser welder, fix at A in the figure. Since there is no lens, alignment and welding can be performed in a short time (2 to 3 minutes), and 95% of the whole exhibits high sensitivity characteristics of 0.8 A / W.

Even when an optical signal of 125 Mbps is received by digital communication using this semiconductor light receiving device, a phenomenon such as waveform distortion and jitter in which the rising and falling portions of the waveform fluctuate with time are not observed at all. .. Also,
Even if this semiconductor light receiving device is used for the light receiving portion of a 40-channel analog image transmission device, the sensitivity is 0.8 A / W.
Is quite sufficient, and even with high sensitivity, a slight amount of leaked light has caused flickering on the screen due to signals with a phase shift, but by using this semiconductor light receiving device, it will not be seen at all. Furthermore, in the charge trapping area with antireflection,
Since it absorbs all unnecessary light, it does not generate reflected light or scattered light that is noise in optical communication.

Thus, the semiconductor light receiving device of the present invention has been expensive until now because it can be mounted on an optical fiber in a short time and the cost can be reduced, and in many applications, the fluctuation of the waveform and the noise are eliminated. For this reason, it will accelerate communication using light, which has been delayed in widespread practical application. Further, as another embodiment of the present invention, the same effect can be obtained even when applied to a butterfly type housing.

[0021]

As described above, according to the present invention, since the photodiode chip is provided with the carrier trapping structure to be invalidated, the signal light from the optical fiber can be transmitted without interposing the lens optical system. Even if it is incident on, the signal will not be distorted. In this way, an inexpensive semiconductor light receiving device that does not use an expensive lens is configured, and a signal with a phase shift is generated when reproducing analog signal light, and the distortion level becomes high. Therefore, it is possible to provide a semiconductor light receiving device that solves the conventional problems such as the above distortion and the inability to perform high-speed communication.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a semiconductor light receiving device according to an embodiment.

FIG. 2 is a diagram showing a relationship between a photodiode chip and an optical fiber according to an essential part of the embodiment.

FIG. 3 is an overall configuration diagram of a conventional example.

FIG. 4 is an overall configuration diagram of a conventional example.

FIG. 5 is a relationship diagram between a photodiode chip and an optical fiber in a conventional example.

[Explanation of symbols]

1 ... Photodiode chip, 2 ... Header, 3 ... Lead, 4 ... Cap, 5 ... Window, 6 ... Optical fiber, 6 '...
Core, 7 ... Ferrule, 8 ... Housing, 9 ... Focusing lens, 11 ... Semiconductor substrate, 12 ... Epitaxial growth layer,
13 ... Diffusion region, 14, 15 ... Electrode, 17 ... Diffusion region.

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[Procedure amendment]

[Submission date] November 20, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

As such a photodiode chip 1 that can be used in the semiconductor light receiving device according to the embodiment of the present invention, a structure for canceling the photocurrent generated by the light incident on the outside of the pn junction which is the light receiving region. (Charge trap type photodiode chip) having
FIG. 2 shows an example thereof. In this structure, a region 17 having the same polarity as the region 13 is formed in the epitaxial layer 12 by thermal diffusion of a metal element. The photocarriers generated in the region 17 do not flow toward the region 13 and disappear in the vicinity of the pn junction between the epitaxial layer 12 and the region 17 or at the pn junction exposed on the chip end face thereof. Specifically, the details are shown in Japanese Patent Application No. 2-230206 by the present applicant.

Claims (1)

[Claims] 1. A header on which a photodiode chip is mounted is fixed to a housing in which an optical fiber is inserted so as to form an integrated structure, and a light receiving surface of the photodiode chip faces a light emitting end surface of the optical fiber. In the semiconductor light receiving device arranged in, the photodiode chip has a pn junction region for outputting a photocurrent as a detection signal on the light receiving surface, and a region for trapping carriers generated around the pn junction region. The semiconductor light receiving device according to claim 1, wherein the light emitted from the optical fiber is immediately incident on the light receiving surface without passing through a lens optical system.