JP3138997B2 - Optoelectronic integrated circuits - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an opto-electronic integrated circuit for receiving light and converting it into an electric signal for use in optical fiber communication or the like.

[0002]

2. Description of the Related Art With the development of optical fiber communication, optical receivers used in this field are required to have high speed. Optoelectronic integrated circuits combining various light receiving elements and transistors have been researched and prototyped in order to satisfy the demand for high speed and realize miniaturization. As a typical example of such an optoelectronic integrated circuit, “S. Chandrasekhar, et al .: IEEE
Photon. Technol. Lett., Vol.3, No.9, 1991, pp.823-
825 ", there is an optoelectronic integrated circuit mounted with a light receiving circuit including a pin photodiode and a heterojunction bipolar transistor.

FIG. 3 is a configuration diagram of this optoelectronic integrated circuit. FIG. 3A is a circuit configuration diagram, and FIG.
4 is a table showing materials forming an n-type photodiode and a heterojunction bipolar transistor (hereinafter, referred to as HBT). As shown, this optical integrated circuit is an InP
InP and InGaAs on a semi-insulating substrate made of crystal
The HBT is formed by using a heterojunction with s and a pin-type photodiode as a light receiving element. here,
Chemical beam epitaxy is used to form the heterojunction layer. Thus, this optoelectronic integrated circuit has characteristics of cut-off frequency (f _T ) = 32 GHz, maximum oscillation frequency (f _MAX ) = 28 GHz, and is operable at a reception information speed of 5 Gb / s. Has been realized.

[0004]

The conventional optoelectronic integrated circuit is constructed as described above, and the light absorbing layer of the light receiving element and the HBT
Was formed based on the same substance, and its band gap was the same. Therefore, light generated by luminous recombination due to current inside the base layer during operation of the HBT is absorbed by the light absorbing layer of the light receiving element to generate a noise current, and a highly sensitive optoelectronic integrated circuit for receiving light is required. There was a problem that it could not be realized.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a highly sensitive optoelectronic integrated circuit for receiving light with reduced noise current.

[0006]

According to the present invention, there is provided an optoelectronic integrated circuit comprising: (a) a light receiving element having a light absorbing portion made of a first semiconductor material on a semi-insulating substrate; A heterojunction bipolar transistor formed by forming an emitter portion and a collector portion in regions opposed to each other across a base portion made of a second semiconductor material having a band gap width smaller than the band gap width of the semiconductor material; Is monolithically included.

Here, the first semiconductor material is GaInAs.
P, and the second semiconductor material is GaInAs.

[0008] The light receiving element may be any one of a pin type photodiode, a metal-semiconductor-metal photodetector, and an avalanche photodiode.

[0009]

In the optoelectronic integrated circuit of the present invention, an HBT in which a current flows through the base portion when there is no external light reception exists near the light receiving element, and generates light according to the band gap of the base portion by radiative recombination. May be. However, even if this light is applied to the light absorbing part of the light receiving element, the light absorbing part of the light receiving element does not absorb the light because the band gap of the light absorbing part is larger than the band gap of the base part of the HBT. do not do.

In addition, even when there is external light reception, an HBT through which a current flows through the base portion is present near the light receiving element (for example, the first stage HBT to which the output of the light emitting element is input). Light corresponding to the band gap of the base may be generated. Even in this case,
Even if this light is applied to the light absorbing part of the light receiving element, the light absorbing part does not absorb the light because the band gap of the light absorbing part of the light receiving element is larger than the band gap of the base part of the HBT.

In this way, only light received from the outside is absorbed by the light absorbing portion of the light receiving element, and an electric signal corresponding to the absorbed amount is output from the optoelectronic integrated circuit.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a circuit configuration diagram of an optoelectronic integrated circuit according to an embodiment, and FIG. 2 is a cross-sectional structure diagram of a portion including a light receiving element and a first stage HBT.

As shown in FIG. 1, this device comprises a pin type photodiode 100 which exhibits conductivity by receiving light,
H for receiving, amplifying, and shaping an electric signal generated by the change in the conductivity of the pin photodiode 100
Transistor group 200 including BTs 210 _{1 to} 210 ₅
And electrical passive elements such as resistors and capacitors for setting operating conditions of the HBTs 210 _{1 to} 210 ₅ .
An electric signal corresponding to the amount of light incident on the pin photodiode 100 from outside is output.

The components of this device are formed on a semi-insulating substrate 300 made of InP crystal (see FIG. 2). The pin photodiode 100 includes a substrate 300
Layer 110 made of InP crystal containing n-type impurities at a high concentration and a GaInAsP mixed layer formed on the surface of the cathode layer 110 and having a low or substantially no impurity content. It has a three-layer structure of a light absorption layer 120 made of a crystal and an anode layer 130 made of an InP crystal formed on the surface of the light absorption layer 120 and containing a high concentration of p-type impurities. Electrodes 411 and 412 are formed on part of the surfaces of the cathode layer 110 and the anode layer 120, respectively, and wiring is provided.

The HBTs 210 _{1 to} 210 ₅ have a similar structure. The structure, the output signal of the pin photodiode 100 as shown in FIG. 2 and input to the base terminal, will be described as a representative in HBT210 ₁ having the function of signal amplification.
The HBT 210 ₁ is formed on the surface of the substrate 300 and n
Layer 211 made of a GaInAs mixed crystal containing a high concentration of impurities of the type, a collector layer 212 formed of a GaInAs mixed crystal having n-type conductivity formed on the surface of the subcollector layer 211, and a surface of the collector layer A base layer 213 made of GaInAs mixed crystal having p-type conductivity and a base layer 213 formed on the surface of the base layer 213;
An emitter layer 214 made of GaInAs mixed crystal containing a high concentration of n-type impurities has a four-layer structure. Sub-collector layer 211, base layer 213, and emitter layer 214
The electrodes 421, 422, and 423
Are formed, and wiring is further provided.

The electrically passive element group is composed of a resistor, a capacitor, and the like formed on the substrate by a known method, and is connected to the above-mentioned active elements such as the pin-type photodiode 100 and the transistor group 200 by wiring. The function of the device is realized in cooperation with the element.

In FIG. 2, the pin type photodiode 100 is not formed directly on the surface of the substrate 300. This is because a method of forming each layer of the pin type photodiode after forming each layer of the HBT 200 on the surface of the substrate 300 is adopted. Even if it is formed directly on the surface of the substrate 300, the same operation and effect as in the present embodiment are obtained.

A reverse bias voltage is applied to the pin photodiode 100, and the light absorbing layer 120 is depleted in a state where no light is received. Light incident on the pin photodiode 100 from the outside excites photocarriers while attenuating exponentially according to the light absorption coefficient. The photocarriers generated in the depletion layer are accelerated by the depletion layer electric field, and generate a current flowing from the anode layer 130 to the cathode layer 110. Note that light absorption is caused by the anode layer 1
The photocarriers are also generated in the layer 30 and the cathode layer 110 to excite the photocarriers. However, since these layers are thin, the excitation probability of the photocarriers is low, and the movement of the photocarriers is caused by diffusion. The amount of generated current is much smaller than the amount of generated current due to light absorption in the depletion layer.

The current generated by the incident light is input to an amplifying / shaping circuit constituted by a transistor group 200 and an electrically passive element group provided at the subsequent stage, and finally an electric signal reflecting the amount of incident light is obtained. Is output.

At the time of the above amplification / shaping operation, a base current flows through each HBT. The base layer 213 of each HBT is G
Since it is made of aInAs mixed crystal, luminescent recombination occurs due to the base current, and light having a wavelength corresponding to the band gap value of the base layer 213 is generated. This light is transmitted to the light absorbing layer 12.
0, but the light absorption layer 120 is GaInA
Since it is made of an sP mixed crystal, its band gap value is larger than the band gap value of the base layer 213, and this light is not absorbed. Therefore, the pin photodiode 1
In the case of 00, a current faithful to the amount of light received from the outside is generated, and an electric signal faithful to the amount of light received can be obtained as an output of the optoelectronic integrated circuit.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, although a pin photodiode is used as a light receiving element in the embodiment, an avalanche photodiode or a metal-semiconductor-metal photodetector may be used. Further, a semiconductor material other than the semiconductor material used in the embodiment may be adopted in consideration of the band gap value.

[0022]

As described in detail above, in the optoelectronic integrated circuit of the present invention, the light absorbing portion of the light receiving element is formed of a material having a band gap larger than that of the material forming the base of the HBT. The light absorption part of the light receiving element does not absorb the light due to the radiative recombination of the base part caused by the
A high-sensitivity optoelectronic integrated circuit with suppressed noise can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an optoelectronic integrated circuit according to an embodiment of the present invention.

FIG. 2 is a structural diagram of an optoelectronic integrated circuit according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a conventional optoelectronic integrated circuit.

[Explanation of symbols]

100 pin photo diode, 110 cathode layer, 120 light absorption layer, 130 anode layer, 200
Heterojunction bipolar transistor, 210: sub-collector layer, 211: collector layer, 212: base layer, 2
13: emitter layer, 300: substrate, 410, 420, 4
30,440,450 ... electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 31/10-31/119 H01L 27/14-27/15

Claims (5)

(57) [Claims] 1. A light receiving element having a light absorbing portion made of a first semiconductor material on a semi-insulating substrate, and a second light receiving device having a band gap width smaller than a band gap width of the first semiconductor material. An optoelectronic integrated circuit, comprising: a heterojunction bipolar transistor formed by forming an emitter and a collector in regions opposed to each other with a base made of a semiconductor material interposed therebetween; 2. The method according to claim 1, wherein the first semiconductor material is GaInAsP.
Wherein the second semiconductor material is GaInAs.
2. The optoelectronic integrated circuit according to claim 1, wherein: 3. The optoelectronic integrated circuit according to claim 1, wherein said light receiving element is a pin type photodiode. 4. The optoelectronic integrated circuit according to claim 1, wherein said light receiving element is a metal-semiconductor-metal photodetector. 5. The optoelectronic integrated circuit according to claim 1, wherein said light receiving element is an avalanche photodiode.