JPH04249382A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To enable incidence of signal light parallel with a package surface of a photodetector without deteriorating dynamic characteristics by providing a diffraction grating to a boundary between a first semiconductor layer and a second semiconductor layer. CONSTITUTION:After a diffraction grating 12 of a period LAMBDA is formed on an N-type semiconductor substrate 11, the diffraction grating 12 is buried by an N-type semiconductor layer 13. After an N-type avalanche layer 14 and an N-type semiconductor layer 15 are laminated and a guard ring 16 and a P-type semiconductor region (photoabsorbing layer) 17 are formed in the N-type semiconductor layer 15, a highly reflecting film 18 and electrodes 19, 20 are laminated. Signal light of wavelength lambda which is vertically directed to the N-type semiconductor substrate 11 of refraction index nj waveguides in the layer, diffracted to satisfy a specified equation in a direction which forms an angle thetato an incidence direction through mutual operation with the diffraction grating 12 of period LAMBDA, and is reflected to the N-type semiconductor layer 13 of refractive index n2. Furthermore, diffracted radiation light is applied to a P-type semiconductor region 17, converted to an electrical signal through photoelectric effect and output from a photodetector element.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a semiconductor photodetector.

0002

[Prior Art] Recent technological advances in trunk optical communication systems are remarkable, and DFB-LDs (Distributed Feedback Laser Diodes), which always oscillate stably in a dynamic single-axis mode, have achieved high efficiency and high sensitivity at the same time. 1Gb with the development and practical application of APD (avalanche photodiode)
Optical communication systems ranging from /s to 2Gb/s have already reached commercialization. Under these circumstances, active research and development is being carried out on next-generation optical communication systems that aim to further increase the distance between repeaters and increase capacity through ultra-high-speed modulation. Among these, in next-generation optical communication systems that aim to increase capacity through ultra-high-speed modulation, the light-emitting element, the drive circuit directly connected to the light-receiving element, and the first stage amplifier are not only integrated circuits for ultra-high-speed operation. When connecting these integrated circuits to light emitting elements and light receiving elements, it is important to avoid generating parasitic capacitance and inductance as much as possible.

[0003] 1Gb/s has reached practical and commercialization so far.
~ In the 2Gb/s trunk optical communication system, various studies have been made regarding the operating speed of each element, but the deterioration of dynamic characteristics caused by these implementations and connections is difficult to solve since the operating range is relatively low frequency. Due to this, sufficient consideration and countermeasures were not taken. Specifically, the light-emitting element, light-receiving element, drive circuit, and first-stage amplifier are individually enclosed in individual packages, and each element is mounted on a circuit board and then connected using lead wires, etc. Ta. With this method, each element can be thoroughly sorted and screened in advance, so it is possible to check not only various electrical and optical characteristics, but also operation speed and reliability. However, the major disadvantage is that the individual packages enclosing the elements have parasitic capacitance and parasitic inductance, so mounting and connecting these elements deteriorates the dynamic characteristics. It also has Therefore, this method is extremely effective because ~
For ultra-high-speed modulation up to the modulation speed range of 2 Gb/s, it is necessary to establish new methods for mounting methods and connecting methods between individual elements.

This new method involves mounting the light emitting element and the light receiving element in close proximity to the driver circuit and the first-stage amplifier integrated circuit, respectively, and connecting them with bonding wires of about 1 mm (bare chip mounting). )
, A method of forming a mounting pattern for a light-emitting element and a light-receiving element on an integrated circuit in advance, and then mounting a light-emitting element and a light-receiving element thereon to connect the integrated circuit (flip-chip mounting). , a method of forming the light-receiving element itself on each integrated circuit to form an integrated element (OEIC
). When mounting and connecting elements capable of sufficiently high-speed operation using each mounting method, the operable modulation frequency range is up to approximately 5 GHz with bare chip mounting, approximately 10 GHz with flip chip mounting, and even higher frequencies with OEIC. It is estimated that up to the area.

[0005] Light-emitting/light-receiving modules installed in 2.5 Gb/s trunk communication systems based on SONET have recently been the most actively developed in terms of increasing communication capacity through ultra-high-speed modulation. Among these, for light-emitting modules with built-in drive circuits and light-receiving modules with built-in first-stage amplifier integrated circuits, consideration has been given to mounting and connections between elements, and implementation using bare chips has already been attempted. In particular, the first stage amplification integrated circuit is mounted close to the light receiving element and connected with bonding wire.
A light-receiving module with a built-in first-stage amplifier integrated circuit has a relatively simple structure as a module because the light-receiving element itself does not generate heat, and there is a strong demand for development compared to a light-emitting module with a built-in drive circuit.

FIG. 3 is a simplified configuration diagram of a conventional light emitting module with a built-in first stage amplifier integrated circuit. After the signal light emitted from the optical fiber 131 is focused by the SELFOC lens 133, it enters the light receiving element 31 and is converted into an electrical signal by the photoelectric effect. The light receiving element 31 is mounted on a pedestal 36 in close proximity to the first stage amplification integrated circuit 33, and the converted electrical signal is input to the first stage amplification integrated circuit 33 through the bonding wire 32 and amplified without interfering with high-speed operation. The light is further transmitted through an electrode pattern 34 formed on the circuit board, passes through an output terminal 35, and is output from the light receiving module with a built-in first-stage amplifier integrated circuit.

[0007]

[Problem to be solved by the invention] As mentioned above, 2Gb/
In order to achieve ultra-high-speed modulation faster than s, the photodetector and first-stage amplifier must be mounted close to each other on the same plane, with a distance of approximately 1 mm.
It is necessary to connect with some bonding wire. In addition, when considering mounting on an actual device or printed board, the light emitting module itself must be in a form that can be mounted on a plane, that is, the optical fiber that inputs the optical signal and the output terminal of the light receiving module are parallel to the same plane. It is also required that the shape be such that However, in the conventional light-receiving module with a built-in first-stage amplifier integrated circuit, it is difficult to make the mounting surface of the light-receiving element, the mounting surface of the first-stage amplifier integrated circuit, and the mounting surface of the light-emitting module itself parallel to each other. This is because the input direction of the signal light needs to be positioned so that the light receiving surface of the light receiving element is orthogonal to each other, and for this reason, for example, the light receiving element and the first stage amplification integrated circuit may be placed close to each other on the same plane. In the conventional example shown in Fig. 3, which is implemented with Since it is in-plane, deterioration of high-speed response cannot be avoided when transmitting electrical signals along the electrode pattern on the circuit board. In this way, in order to take full advantage of the greatest advantage of bare-chip mounting, which is that high-speed response does not deteriorate due to mounting or connection between elements, in the light receiving module, the optical fiber that inputs the optical signal and the light receiving The biggest problem is how to realize a structure in which the output terminals of the module are parallel to the same plane.

A possible solution to this problem is to modify the optical coupling system to determine the input direction of the optical signal to the light receiving element. Figure 4 is a simplified configuration diagram of a light receiving module with a built-in first-stage amplifier integrated circuit using Pelican Building fiber, which has been realized by directly processing the tip of the optical fiber to make the direction of the optical fiber and the input direction of the optical signal orthogonal. be. The tip of the Pelicanville fiber 142 is pre-processed to have a bulbous tip, and the tip of the optical fiber is polished obliquely to reflect the signal light, making it possible to make the direction of the optical fiber orthogonal to the output direction of the optical signal. The signal light is reflected by the pelican building fiber 142 in a direction perpendicular to the direction of the optical fiber, and then enters the light receiving element 41 where it is converted into an electrical signal by the photoelectric effect. Since the light receiving element 41 is mounted in close proximity to the first stage amplification integrated circuit 43, the converted electrical signal is input to the first stage amplification integrated circuit 43 through the bonding wire 42 and amplified without interfering with high-speed operation. The light is connected to an output terminal 45 through an extremely short electrode pattern 44 formed on the substrate, and is output from the light-receiving and light-receiving module with a built-in first stage amplifier integrated circuit.

In this example, by using a pelican building fiber, the mounting surface of the light receiving element, the mounting surface of the first stage amplifier integrated circuit, and the output terminal from the light receiving module, that is, the mounting surface of the light receiving module itself can be made parallel to each other. Therefore, the dynamic characteristics will not deteriorate due to the mounting and connection of the elements, but on the other hand, it is not easy to manufacture the Pelican Building fiber itself and the reproducibility is poor, and the complicated shape causes loss within the fiber. This has the disadvantage that it is difficult to obtain sufficient photoelectric efficiency and high receiving sensitivity.

0010

[Means for Solving the Problems] A semiconductor light receiving element of the present invention includes a first semiconductor layer of a first conductivity type into which received light is incident;
a second semiconductor layer of a first conductivity type that has a smaller band gap than the first semiconductor layer and is in contact with the first semiconductor layer;
It is characterized by having at least semiconductor junctions of first and second conductivity types, and having a diffraction grating at the boundary between the first semiconductor layer and the second semiconductor layer.

[0011]

Embodiment 1 Next, the present invention will be explained in detail with reference to the drawings. FIG. 1 is a cross-sectional view of the structure of a semiconductor light-receiving element showing Example 1 of the present invention. The semiconductor photodetector of the present invention forms a diffraction grating 12 with a period Λ on an n-type semiconductor substrate 11, and then buries the diffraction grating 12 with an n-type semiconductor layer 13.
Laminating an n-type avalanche layer 14 and an n-type semiconductor layer 15,
After forming a guard ring 16 and a p-type semiconductor region (light absorption layer) 17 on the n-type semiconductor layer 15, a high-reflection film 18 and electrodes 19 and 20 are laminated. Signal light with a wavelength λ that is perpendicularly incident on the n-type semiconductor substrate 11 with a refractive index nj is guided within the layer, and due to interaction with the diffraction grating 12 with a period Λ, the signal light is directed at an angle θ with respect to the direction of incidence. The n-type semiconductor layer 13 is diffracted to satisfy the following formula and has a refractive index n2.
is radiated to.

0012

Further, the diffracted radiation light enters the p-type semiconductor region (light absorption layer) 17, is converted into an electric signal by the photoelectric effect, and is output from the light receiving element. At this time, if the radiation light that can be received satisfies θ~π/2, that is,

[
0014

The incident light that can be received is theoretically limited to

[0016]

The wavelength is limited to the wavelength that satisfies the following. In addition, the photoelectric efficiency of a normal photodetector is said to be about 80%, and some of it passes through the photodetector without being converted into an electrical signal.
In this embodiment, the p-type semiconductor region (light absorption layer) 17
A highly reflective film 18 is formed in contact with the light to reflect the passing light and make it enter the light absorption layer again to improve photoelectric efficiency. By forming a light-receiving element using the diffraction phenomenon of the signal light by the diffraction grating in this way, it becomes possible to input the signal light parallel to the mounting surface of the light-receiving element, and the mounting and connection of the element A light receiving module with a built-in first stage amplifier integrated circuit can be manufactured without deteriorating dynamic characteristics. In this example, an avalanche photodiode having an avalanche layer is used as the semiconductor light-receiving element, but the present invention is not particularly limited.

[0018]

Embodiment 2 FIG. 2 is a sectional view of the structure of a semiconductor light receiving element showing Embodiment 2 of the present invention. The semiconductor photodetector of the present invention has a refractive index nj on an n-type semiconductor substrate 11 with a refractive index n3.
After stacking n-type semiconductor layers 121 with (n3 < nj ) and forming a diffraction grating 12 with a period Λ on the surface thereof, the diffraction grating 12 is formed with an n-type semiconductor layer 13 with a refractive index n2 (n2 < n3 < nj ). Buried, n-type avalanche layer 1
4. After stacking the n-semiconductor layer 15 and forming the guard ring 16 and the p-type semiconductor region (light absorption layer) 17 on the n-semiconductor layer 15, the high reflection film 18, electrodes 19, 20, and reflective mirror 122 are formed. It is manufactured by Signal light with a wavelength λ that is perpendicularly incident on the n-type semiconductor layer 121 with a refractive index nj is guided within the layer as in the case of Example 1, and is guided through the diffraction grating 1 with a period Λ.
2, it is diffracted and radiated in a direction forming an angle θ with respect to the incident direction. The synchrotron radiation has a refractive index n2
The p-type semiconductor region (light absorption layer) 17 passes through the type semiconductor layer 13
The light is incident on the light, is converted into an electrical signal by the photoelectric effect, and is output from the light receiving element.

In this embodiment as well, by forming the light receiving element by utilizing the diffraction phenomenon of signal light by the diffraction grating,
It becomes possible to make the signal light incident parallel to the mounting surface of the light-receiving element, and it is possible to manufacture a light-receiving module with a built-in first-stage amplification integrated circuit without deteriorating the dynamic characteristics due to element mounting and connection. In particular, in this example, since the refractive index is changed in contact with the waveguide layer (n-type semiconductor layer 121) for signal light, the confinement of light within the waveguide layer is stronger than in Example 1. Not only does the diffraction efficiency improve compared to the above, but even though a high reflection film 18 is formed in contact with the p-type semiconductor region (light absorption layer) 17 and a reflecting mirror 122 is formed in contact with the n-type semiconductor substrate, it is possible to redirect the reflected light. The photoelectric efficiency can be further improved by entering the light absorption layer. In this example as well, an avalanche photodiode having an avalanche layer was used as the semiconductor light-receiving element, but as in Example 1, this is not particularly limited.

[0020]

[Effects of the Invention] As explained above, since the semiconductor photodetector of the present invention has a diffraction grating within the photodetector, the photodetector can be formed by utilizing the diffraction phenomenon of signal light by the diffraction grating. Since it is possible to make the signal light incident parallel to the mounting surface of the light receiving element, the mounting of the element,
This has the effect that dynamic characteristics are not degraded by the connection.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the structure of a semiconductor light-receiving device showing Example 1 of the present invention;

FIG. 2 is a cross-sectional view of the structure of a semiconductor light-receiving device showing Example 2 of the present invention;

[Figure 3] A simple configuration diagram of a conventional light receiving module with a built-in first-stage amplifier integrated circuit,

FIG. 4 is a simple configuration diagram of a light receiving module with a built-in first-stage amplifier integrated circuit using a Pelican building fiber.

[Explanation of symbols]

11 n-type semiconductor substrate 12 diffraction grating 13 n-type semiconductor layer 14 n-type avalanche layer 15 n-type semiconductor layer 16 guard ring 17 p-type semiconductor region (light absorption layer) 18
High reflective film 19, 20 electrode

Claims (1)

[Claims] 1. A first semiconductor layer of a first conductivity type into which received light is incident, and a second semiconductor of a first conductivity type that is in contact with the first semiconductor layer and has a smaller band gap than the first semiconductor layer. A semiconductor light-receiving element having at least a layer and semiconductor junctions of first and second conductivity types, the semiconductor light-receiving element having a diffraction grating at the boundary between the first semiconductor layer and the second semiconductor layer. .