JPH0750404A - Optoelectronic integrated circuit - Google Patents

Abstract

PURPOSE:To provide a high sensitive photo-receiving or photo-transmitting and receiving optoelectronic integrated circuit by reducing the generation of dark current. CONSTITUTION:A low reflectance layer 11 comprising Ti and a bonding layer 12 comprising Au are successively lamination-formed on the rear surface of a semi-insulating substrate 10 comprising InP crystal. On the other hand, a pin-PD 20 and an HBT 30 are monolithically and integrally formed on the surface of the substrate 10. In such a constitution, light is emitted by light emitting recoupling in the base layer during the operation time of the latter 30 so as to emit the incident light to the former 20 in index-functionally attenuable mode while the photocomponent in wavelength sensitive to the PD 20 is absorbed into the layer 11 on the rear surface of the substrate 10 to be reflected thereon with the photointensity thereof reduced to fractions reaching the photoabsorbent layer for reducing the dark current so that the current corresponding to externally detected photo-amount may be generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optoelectronic integrated circuit (OEIC) in which an optical element and an electronic element are monolithically integrated and used for optical fiber communication or the like.

[0002]

2. Description of the Related Art Conventionally, on a surface of a semi-insulating substrate made of InP or the like, a pin type photodiode (pin-P) is used as a reception front end used for optical fiber communication.
An optoelectronic integrated circuit has been developed in which a light receiving element such as D) is monolithically integrated with a light emitting element such as a laser diode (LD) or an electronic element such as a heterojunction bipolar transistor (HBT) as a transmission front end. In addition, it has a high-speed communication function and is downsized.

Regarding such prior art, reference is made to "Chandrasekhar, S.et.al., IEEE Photon.Technol.Let."
t., vol.3, no.9, pp.823-825, 1991 "and the like.

[0004]

However, in the above-mentioned conventional optoelectronic integrated circuit, light is emitted due to the radiative recombination due to the electric current inside the base layer during the operation of the HBT. Light is also emitted from the active layer of the LD. These lights may reach and be absorbed by the light absorption layer of the pin-PD that is the light receiving element, and the main path is via reflection on the back surface of the semi-insulating substrate. Therefore, since the generation of dark current increases in the pin-PD, there is a problem that the generation of noise signals increases as the output of the optoelectronic integrated circuit.

Therefore, the present invention has been made in view of the above problems, and provides an optoelectronic integrated circuit for high-sensitivity optical reception or optical transmission / reception by reducing the generation of dark current. With the goal.

[0006]

In order to achieve the above object, the present invention provides a first light receiving element on the surface of a substrate,
In an optoelectronic integrated circuit in which at least one of a light emitting element, an electronic element, and a second light receiving element is monolithically integrated and formed, a wavelength of a wavelength having sensitivity to the first or second light receiving element is provided on a back surface of a substrate. A low reflectance layer that absorbs light is formed.

The low reflectance layer may be formed of Ti having a layer thickness of 10 nm or more.

The first or second light receiving element is
It may be characterized by being arranged two-dimensionally.

Further, the first or second light receiving element is
It may be a pin type photodiode, an avalanche photodiode, or a metal-semiconductor-metal photodetector.

The light emitting element may be either a light emitting diode or a laser diode.

The electronic device may be a heterojunction bipolar transistor or a PN junction diode.

Further, the substrate may be made of InP.

[0013]

According to the present invention, an optoelectronic integrated circuit in which a first light receiving element and at least one of a light emitting element, an electronic element and a second light receiving element are monolithically integrated on the surface of a substrate. In, on the back surface of the substrate,
A low-reflectance layer that absorbs light having a wavelength having sensitivity is formed in the first or second light receiving element. Inside this optoelectronic integrated circuit, light is emitted from the electronic element due to radiative recombination during operation, or light is emitted from the light emitting portion of the light emitting element during operation. In addition, external incident light is transmitted and emitted from the first or second light receiving element.

However, this emitted light is absorbed by the low-reflectance layer on the back surface of the substrate at a wavelength having a sensitivity to the first or second light-receiving element, and is reflected with reduced light intensity. Therefore, in the first or second light receiving element,
Since the dark current generated when this reflected light reaches the light absorption layer is reduced, a current faithful to the amount of light received from the outside is generated and output from the optoelectronic integrated circuit as an electrical signal corresponding to the amount of light received from the outside. To be done.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of an embodiment according to the present invention will be described below with reference to FIGS. In addition,
In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 shows the configuration of a first embodiment according to the optoelectronic integrated circuit of the present invention.

On the back surface of the semi-insulating substrate 10 made of InP crystal, a low reflectance layer 11 and a bonding layer 12 are sequentially laminated. This semi-insulating substrate 10 is
It has a high transmittance for light having a wavelength of about 1.3 μm. The low-reflectance layer 11 is formed by depositing Ti and has a penetration depth of about 23 with respect to light having a wavelength of about 1.3 μm.
nm, the layer thickness is about 10 nm or more, preferably about 1/2 of the penetration length or more, and the wavelength is about 1.3 μ.
It is formed so as to have a low reflectance for the light of m. Further, the bonding layer 12 is formed by depositing Au or the like, which improves the adherence to the package or the like during die bonding.

On the surface of the semi-insulating substrate 10, the pin-PD 20 which is a light receiving element is an HBT which is an electronic element.
It is formed by monolithically integrating with 30. In this pin-PD 20, a cathode layer containing a high concentration of n-type impurities, a light absorption layer having a low impurity content or substantially no impurities and having sensitivity to light having a wavelength of about 1.3 μm, And an anode layer containing a high concentration of p-type impurities are sequentially laminated on the semi-insulating substrate 10 to form a three-layer structure. Electrodes are partially formed on the surfaces of the cathode layer and the anode layer, and wirings connected to these are provided.

Further, in the HBT 30, the sub-collector layer containing n-type impurities in high concentration, the collector layer having n-type conductivity, the base layer having p-type conductivity, and the n-type impurities in high concentration. The included emitter layer is sequentially laminated on the semi-insulating substrate 10 to have a four-layer structure. Electrodes are partially formed on the surfaces of the subcollector layer, the base layer, and the emitter layer, and wirings connected to these are provided.

Next, the operation of the first embodiment will be described.

In the pin-PD 20, the reverse bias voltage is applied, so that the light absorption layer is depleted in the state where no light is received. When this pin-PD 20 is irradiated with external light having a wavelength of about 1.3 μm from the surface side of the semi-insulating substrate 10, photocarriers are excited in the light absorption layer with a high probability and accelerated by the electric field of the depletion layer to cause the cathode. Generates a current that flows from the layer to the anode layer.

The current output from the pin-PD 20 in this manner is input to the base layer of the HBT 30. During the operation of the HBT 30, radiative recombination due to the base current occurs in the base layer, so that light having a wavelength corresponding to the bandgap value of the base layer is emitted. Further, the light incident on the pin-PD 20 passes through the anode layer, the light absorption layer, and the cathode layer,
The light is emitted from the pin-PD 20 while being exponentially attenuated corresponding to each light absorption coefficient.

However, the low reflectance layer 11 is formed of Ti having a layer thickness of about 10 nm or more. Therefore, the emitted light from the pin-PD20 and HBT30 is
On the back surface of the semi-insulating substrate 10, the low-reflectance layer 11 absorbs a light component having a wavelength sensitive to the pin-PD 20, and reduces the light intensity of the light component to a fraction and reflects it.

As a result, in the pin-PD 20, the dark current generated by the reflected light reaching the light absorption layer is reduced, so that a current faithful to the amount of light received from the outside is generated. Therefore, this current is amplified and shaped by the HBT 30,
It is output from the optoelectronic integrated circuit as an electric signal corresponding to the amount of light received from the outside.

FIG. 2 shows the configuration of the second embodiment of the optoelectronic integrated circuit of the present invention.

The present embodiment is constructed almost in the same way as the first embodiment. However, on the surface of the semi-insulating substrate 10, a plurality of light-receiving elements, that is, the pin-PDs 20a to 20a.
c are arranged two-dimensionally and are monolithically integrated and formed. Each of the pin-PDs 20a to 20c has substantially the same configuration as that of the first embodiment, and the semi-insulating substrate 1 is used.
Channels are formed by coupling with optical fibers on the surface side of 0, respectively.

Next, the operation of the second embodiment will be described.

In each of the pin-PDs 20a to 20c, the reverse bias voltage is applied, so that the light absorption layer is depleted in the state where no light is received. Each pin-PD2
When 0a to 20c are irradiated with light having a wavelength of about 1.3 μm from the optical fiber, photocarriers are excited in the light absorption layer with high probability and are accelerated by the depletion layer electric field to generate a current flowing from the cathode layer to the anode layer. To do. Further, this incident light is emitted from each of the pin-PDs 20a to 20c while being attenuated exponentially corresponding to each light absorption coefficient as it passes through the anode layer, the light absorption layer, and the cathode layer.

However, the low reflectance layer 11 is formed of Ti having a layer thickness of about 10 nm or more. Therefore, the emitted light from the pin-PDs 20a to 20c is pi due to the low reflectance layer 11 on the back surface of the semi-insulating substrate 10.
The n-PDs 20a to 20c absorb a light component having a wavelength having a sensitivity, reduce the light intensity of the light component to a fraction, and are reflected.

As a result, in the pin-PDs 20a to 20c, the dark current generated by the reflected light reaching the light absorption layer is reduced, so that a current faithful to the amount of light received from the outside is generated. Therefore, since the channels corresponding to the respective pin-PDs 20a to 20c are electrically and optically sufficiently separated from each other, the current thus output corresponds to the amount of light received from the outside. The electric signal is output from the optoelectronic integrated circuit.

FIG. 3 shows the configuration of a third embodiment of the optoelectronic integrated circuit of the present invention.

This embodiment is constructed almost in the same way as the first embodiment. However, on the surface of the semi-insulating substrate 10, the pin-PD 20 which is a light receiving element is formed monolithically integrated with the LD 40 which is a light emitting element. The pin-PD 20 has a structure similar to that of the first embodiment.

In the LD 40, the n-type cladding layer containing a high concentration of n-type impurities, the active layer having p-type conductivity, and the p-type cladding layer containing a high concentration of p-type impurities are semi-insulating. The layers are sequentially stacked on the substrate 10 to have a double heterojunction structure. Electrodes are partially formed on the surfaces of the n-type clad layer and the p-type clad layer, and wirings connected to these are provided.

Next, the operation of the third embodiment will be described.

In the pin-PD 20, since the reverse bias voltage is applied, the light absorption layer is depleted in the state where no light is received. When this pin-PD 20 is irradiated with external light having a wavelength of about 1.3 μm from the surface side of the semi-insulating substrate 10, photo carriers are excited with high probability in the light absorption layer and accelerated by the electric field of the depletion layer to cause the cathode. Generates a current that flows from the layer to the anode layer.

On the other hand, in the LD 40, when a forward bias voltage is applied as a trigger, the electrons injected from the n-type cladding layer are confined in the active layer. In this active layer, the light generated by stimulated emission is gradually amplified, and finally laser-oscillates to be emitted from the LD 40. Also, pi
The light incident on the n-PD 20 is attenuated exponentially in accordance with the respective light absorption coefficients as it passes through the anode layer, the light absorption layer, and the cathode layer, and
-It is released from PD20.

However, the low reflectance layer 11 is formed of Ti having a layer thickness of about 10 nm or more. Therefore, the light emitted from the pin-PD 20 and the LD 40 is p-typed by the low reflectance layer 11 on the back surface of the semi-insulating substrate 10.
The in-PD 20 absorbs a light component of a wavelength having sensitivity, reduces the light intensity of the light component to a fraction, and is reflected.

As a result, in the pin-PD 20, the dark current generated by the reflected light reaching the light absorption layer is reduced, so that a current faithful to the amount of light received from the outside is generated. Therefore, since the pin-PD 20 and the LD 40 are optically sufficiently separated from each other, the current output in this way is used as an output of the optoelectronic integrated circuit and an electric signal corresponding to the amount of light received from the outside. Is output as.

The present invention is not limited to the above embodiments, but various modifications can be made.

For example, in the above-mentioned embodiments, the pin-PD is used as the light receiving element, but the same applies when an avalanche photodiode (APD) or a metal-semiconductor-metal photodetector (MSM photodetector) is used. The effect is obtained.

Although the HBT is used as the electronic element in the above-mentioned embodiments, the same effect can be obtained by using the PN junction diode.

Further, although the LD is used as the light emitting element in the above-mentioned embodiments, the same effect can be obtained by using the light emitting diode (LED).

[0043]

As described above in detail, according to the present invention, the first light receiving element, the light emitting element, and the
In an optoelectronic integrated circuit in which at least one of an electronic element and a second light receiving element is monolithically integrated, light having a wavelength sensitive to the first or second light receiving element is provided on the back surface of the substrate. A low reflectance layer that absorbs is formed. Inside this optoelectronic integrated circuit, light is emitted from the electronic element due to radiative recombination during operation, or light is emitted from the light emitting portion of the light emitting element during operation.
In addition, external incident light is transmitted and emitted from the first or second light receiving element.

However, this emitted light is absorbed by the low-reflectance layer on the back surface of the substrate at a wavelength having a sensitivity to the first or second light-receiving element, and is reflected with reduced light intensity. Therefore, in the first or second light receiving element,
Since the dark current generated when this reflected light reaches the light absorption layer is reduced, a current faithful to the amount of light received from the outside is generated and output from the optoelectronic integrated circuit as an electrical signal corresponding to the amount of light received from the outside. To be done. Therefore, by reducing the noise signal, it is possible to provide a highly sensitive optoelectronic integrated circuit for optical reception.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of a first embodiment according to an optoelectronic integrated circuit of the present invention.

FIG. 2 is a sectional view showing a configuration of a second embodiment according to the optoelectronic integrated circuit of the present invention.

FIG. 3 is a cross-sectional view showing the configuration of a third embodiment according to the optoelectronic integrated circuit of the present invention.

[Explanation of symbols]

10 ... Semi-insulating substrate, 11 ... Low reflectance layer, 12 ... Bonding layer, 20 ... Pin-PD, 30 ... HBT, 40 ...
LD.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kentaro Michiguchi 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works

Claims (7)

[Claims] 1. An optoelectronic integrated circuit in which a first light receiving element and at least one of a light emitting element, an electronic element, and a second light receiving element are monolithically integrated on a surface of a substrate, wherein the substrate An optoelectronic integrated circuit characterized in that a low-reflectance layer that absorbs light having a wavelength sensitive to the first or second light receiving element is formed on the back surface of the. 2. The optoelectronic integrated circuit according to claim 1, wherein the low reflectance layer is formed of Ti having a layer thickness of 10 nm or more. 3. The optoelectronic integrated circuit according to claim 1, wherein the first or second light receiving element is two-dimensionally arranged. 4. The first or second light receiving element is pi
2. The optoelectronic integrated circuit according to claim 1, wherein the optoelectronic integrated circuit is an n-type photodiode, an avalanche photodiode, or a metal-semiconductor-metal photodetector. 5. The optoelectronic integrated circuit according to claim 1, wherein the light emitting element is one of a light emitting diode and a laser diode. 6. The optoelectronic integrated circuit according to claim 1, wherein the electronic element is either a heterojunction bipolar transistor or a PN junction diode. 7. The optoelectronic integrated circuit according to claim 1, wherein the substrate is made of InP.