JPH0575159A - Optical semiconductor device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of transistor characteristics due to the residual resistance effect and current concentration effect and lessen the chip size by providing a light entrance window or the electrodes in emitter area section of bipolar transistor-type optical semiconductor device. CONSTITUTION:A P-type semiconductor layer 12 is formed to comprise a base area on an N-type semiconductor layer 11 forming a collector area, and further an N-type semiconductor 13 is formed to comprise an emitter area on the layer 12. Then, electrodes 14 are provided on the layer 13 and simultaneously the area on the emitter area excluding the electrodes 14 is used as a light entrance window 15. Thanks to such construction, the enlarged emitter area can be utilized as it is as a light absorbing area, resulting in reduction of chip area. On the other hand, when a light 18 enters uniformly, collector current will flow evenly in a whole emitter area and there occurs no lowering of transistor efficiency resulting from the concentration of collector current to the periphery of emitter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device,
In particular, it relates to a bipolar transistor type optical semiconductor device.

[0002]

2. Description of the Related Art A conventional optical semiconductor device, in particular, a bipolar transistor type optical semiconductor device has a structure shown in FIG. The example shown in FIG. 3A is an example of an NPN type phototransistor, in which a semiconductor layer 32 forming a base region is formed on a semiconductor layer 31 forming a collector region, and an emitter region is formed in a part of the base region. The semiconductor layer 33 forming the is formed. An electrode 34 is formed on the semiconductor layer 33 forming the emitter region so as to cover the emitter region. That is, FIG.
In (a), the PN junction of the transistor structure portion in the region B is covered with the electrode, so that the structure does not receive the direct light 37. On the other hand, a PN junction with an extended base region,
That is, a diode is formed in the region A in FIG.
The light 37 is absorbed in this portion and photoelectric conversion is performed. Incidentally, reference numerals 35 and 36 in the figure respectively denote a back electrode and a surface protective film.

FIG. 3B is a diagram showing an operating state of the conventional optical semiconductor device described above. That is, the photocurrent 38 generated by the light 37 incident on the diode portion in the region A is injected into the base portion of the transistor in the region B,
Operates as a phototransistor.

[0004]

This conventional optical semiconductor has the following problems. In order to secure the quantum efficiency of light, the optical semiconductor device generally has a structure in which the semiconductor layer in the collector region is thick and the specific resistance is high.
Therefore, the collector current is easily saturated due to the residual resistance effect.
In order to avoid this problem, it is necessary to increase the emitter area, the chip area becomes large, and as a result, there is a problem that the cost tends to be high. On the other hand, FIG.
As shown in (b), the collector current is likely to concentrate on the emitter peripheral portion 39 due to the resistance R of the base region, and there is also a problem that the characteristics of the transistor are deteriorated.

[0005]

The optical semiconductor device of the present invention has a light entrance window in at least a part of the electrode formed so as to be connected to the emitter region of the bipolar transistor.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an optical semiconductor device of the present invention will be described with reference to the drawings. FIG. 1A is a diagram showing the structure of an embodiment of an optical semiconductor device of the present invention. A P-type semiconductor layer 12 forming a base region is formed on an N-type semiconductor layer 11 forming a collector region, and an N-type semiconductor layer 13 forming an emitter region is further formed on the semiconductor layer forming a base region.
Are formed. An electrode 14 is formed on the semiconductor layer 13 forming this emitter region, and at the same time, a region having no electrode is formed as a light incident window 15 on this emitter region. In the figure, reference numerals 16, 17 and 18 denote a back electrode, a surface protective film, and incident light, respectively.

Next, the operation of the optical semiconductor device of the present invention will be described with reference to FIG. The light 18 incident from the light incident window 15 is absorbed by the pn junction of the transistor and injected into the base 12 of the transistor as a photocurrent 19.
As a result, a collector current flows through the transistor.

With such a structure, the enlarged emitter region can be used as it is as a light absorbing region, and as a result, good transistor characteristics can be obtained even if the chip area is small.

Further, since the photocurrent is mainly supplied from the collector region 11 to the base region 12, it is not affected by the base resistance R shown in FIG. 1 (b). If the light 18 is uniformly incident on the emitter region, a collector current flows uniformly over the entire emitter region. That is, the transistor efficiency is not reduced due to the concentration of the collector current around the emitter due to the base resistance, which has occurred in the conventional optical semiconductor device. Specifically, in the conventional semiconductor device, it is necessary to set the emitter width to about 20 μm to 30 μm or less to prevent the current concentration effect, whereas in the optical semiconductor device of the present invention, the emitter width is set to 100 μm or more. If the light incident area is widened, current concentration does not occur essentially. Therefore, deterioration of transistor characteristics due to current concentration can be prevented.

In the case of a PNP type phototransistor, the same effect as above can be obtained.

FIG. 2 is a diagram showing the structure of the second embodiment of the present invention. Here, 21, 22, and 23 are semiconductor layers showing collector, base, and emitter regions, respectively, and 25 is a light incident window. In this structure, the light 28a incident on the area A in the figure is absorbed by the diode portion formed in the area A, and is supplied to the base 22 of the transistor as a photocurrent. Further, the light 28b incident on the transistor portion in the region B is absorbed by the pn junction portion of the transistor portion, is similarly supplied to the base region 22, and is amplified. In this way, also in the case of the second embodiment of the present invention, as in the case of the first embodiment, the light incident from the entrance window 25 effectively becomes the base current, and the same effect as in the case of the first embodiment. Is obtained.

Further, these optical semiconductor devices can be used as a light receiving element of a composite type optical semiconductor device such as a photo coupler and a photo interrupter.

[0013]

As described above, the optical semiconductor device of the present invention has a structure in which at least a part of the electrode formed so as to be connected to the emitter region of the bipolar transistor has a light incident window. There is.

With this structure, the light incident on the transistor region is effectively absorbed and injected into the base as a photocurrent. Therefore, even if the chip size is reduced, good characteristics can be obtained. Further, since the photocurrent is directly injected into the base region from the collector region, it is not affected by the base resistance, and the transistor characteristics are not deteriorated due to the current concentration effect around the emitter.

[Brief description of drawings]

1A is a diagram showing a structure of an optical semiconductor device according to an embodiment of the present invention, and FIG. 1B is a diagram explaining an operation of the optical semiconductor device of the present invention.

FIG. 2 is a diagram showing the structure of an optical semiconductor device according to a second embodiment of the present invention.

FIG. 3A is a diagram showing a structure of a conventional optical semiconductor device,
(B) is a figure explaining operation | movement of the conventional optical semiconductor device.

[Explanation of symbols]

 11, 21, 31 Semiconductor layers forming collector regions 12, 22, 32 Semiconductor layers forming base regions 13, 23, 33 Semiconductor layers forming emitter regions 14, 24, 34 Electrodes 15, 25 Light incident window 16 , 26, 35 Backside electrode 17, 27, 36 Surface protective film 18, 37 Light 28a Light incident on diode portion 28b Light incident on transistor portion 19,38 Photocurrent 39 Current concentration area around emitter

Claims (2)

[Claims] 1. A semiconductor device having an NPN or PNP type bipolar transistor, wherein at least a part of an electrode formed to be connected to an emitter region of the bipolar transistor has a light incident window. Semiconductor device. 2. A photocoupler or photointerrupter type optical semiconductor device in which a light emitting element and a light receiving element are incorporated in the same package, wherein the light receiving element corresponds to claim 1.