JPS6133658Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to communication using an optical fiber as a transmission path, that is, improvement of a bidirectional electrical-to-optical conversion element belonging to an optical semiconductor element for optical fiber communication.

In recent years, optical fiber communication has attracted attention due to its non-electromagnetic induction, light weight, and low transmission loss characteristics, and has been rapidly put into practical use for a variety of applications. A light-emitting/light-receiving semiconductor element is a semiconductor element that combines the functions of a light-emitting element, such as a light-emitting diode, and a light-receiving element, such as a photodiode, used in optical fiber communication equipment, and is capable of processing a single beam of light in a time-sharing manner. This allows the fiber to be used effectively in both directions. In addition to making it possible to use a single optical fiber in both directions without using a bidirectional separation optical circuit, the light-emitting and light-receiving semiconductor device can also replace two parts, a light-emitting element and a light-receiving element, with a single part. It has the advantage of significantly reducing the number of related optical components, and has attracted attention as a key element for simplifying and economicalizing optical transmitter/receivers for data transmission, and has been under development for some time.

For example, various GaAs-
A study of the photodetection characteristics of GaAlAsLEDs and an article published in Electronics Letters published in 1978.
GaAs-
Observations of avalanche multiplication in GaAlAs LEDs have been reported. Furthermore, at the 4th European Optical Communication Conference (1978), it was reported that the characteristics were improved by optimizing the layer thickness and impurity doping amount of the multilayer structure shown in FIG.

A sectional view is shown in FIG. In the conventional example, P type
A confinement _layer 22 made of _P -type Ga _{0 . 65 Al 0 .} an active layer 23 made of n-type Ga _{0.65 Al 0.35} As (thickness 1.5 _μm ), and an active layer 23 made of n-type Ga _0.65 Al _0.35 As (thickness _{1.5 μm} ); Sa2.5
window layer 25 electrodes 26, 27
Signals are input and output through the opening 28.

However, in the above-mentioned conventional example, the light emitting diode was constructed by simply utilizing the photodiode function that the light emitting diode had as a secondary function. For this reason, in the conventional example, even if the performance as a light emitting diode is good, the performance of a photodiode as a light receiving element is unsatisfactory. In other words, in the conventional example, when the diameter of the light emitting region is reduced in an attempt to improve the performance of the light emitting element and obtain a large light output to the optical fiber, when the emitted light from the optical fiber is detected as a light receiving element, the minute emitted light is The drawback was that it required a high-performance optical element and a highly precisely adjusted optical system to effectively focus light on the light-receiving area.

In addition, due to having a common light-emitting region and light-receiving region, for example, in order to obtain good frequency response characteristics during light-emitting operation, an element with a thinner layer thickness in the light-emitting and light-receiving region may absorb light during light-receiving operation. or, conversely, a device with a thick layer in the light-emitting/receiving region may have high light-receiving sensitivity during light-receiving operation, but poor frequency response characteristics during light-emitting operation. I can see the inconvenience.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, and to provide a light-emitting and light-receiving semiconductor device that can easily obtain high light-emitting and light-receiving coupling efficiency when coupled with an optical fiber, and at the same time enable high frequency response characteristics during light-emitting operation. There is a particular thing.

According to the present invention, in a light-emitting and light-receiving semiconductor device that includes a double heterojunction structure composed of a - group compound semiconductor and has a light-emitting and light-receiving opening on the top surface of the device, the device has a forbidden band width narrower than that of adjacent layers. The light emitting and receiving layer has a thickness larger than the reciprocal of the attenuation constant of the light emitting and receiving layer for light having the wavelength of light emitting and receiving, and is located below an area narrower than the light emitting and receiving aperture at approximately the center of the light emitting and receiving aperture. A light-emitting/light-receiving semiconductor element is obtained, which is characterized by having a locally deep Pn junction formed by introducing impurities into the interior of the semiconductor element.

Next, the present invention will be explained in detail with reference to the drawings.
1 and 2 are a plan view and a side sectional view, respectively, of an embodiment based on the present invention. This example belongs to the - group compound semiconductor and has an n-type conductivity type.
A non-doped, conductive type n
The effective attenuation constant for light with the emission wavelength of the shape is 0.5
~ ³ μm thick n-
In _{0 . 76} Ga _{0 . 24} As ₀ . ₅₅ P 0 . Light receiving aperture 1
A zinc diffusion region 14 is formed from the surface on the side of the light emitting/receiving aperture 15 and is deeply diffused only in a small circular area in the center of the light emitting/receiving aperture 15. It has a deep Pn junction 18b. In addition, 18a in the figure is an n- layer formed during liquid phase epitaxial growth.
A shallow Pn junction near the heterojunction between the In ₀ . ₇₆ Ga ₀ . ₅₄ As ₀ . ₅₅ P ₀ . ₄₅ layer 12 and the P-InP layer 13 is shown. n
The side electrode 17 and the P side electrode 16 are each made of well-known tin.
15% gold 75% Au-Sn alloy and zinc 10% gold 90%
It was formed using a vacuum evaporation method using an Au-Zn alloy.

In this embodiment, the P-side electrode 16 is connected to the N-side electrode 17.
By switching the polarity between positive and negative, it can be used as a light emitting element and a light receiving element in a time-sharing manner.
If the P-side electrode 16 is made positive, both the shallow Pn junction 18a and the deep Pn junction 18b will be biased in the forward direction, so that the n-
Minority carrier injection is performed into the In _{0 . 76} Ga _{0 . 24 As} 0 . 55 P 0 _{.
In 0.76} Ga _{0.24 As 0.55} P _0.45 Forbidden band _width of layer 12 approximately _0.95eV
Corresponding to this, light emission with a wavelength of 1.3 μm is generated. A small number of carrier injections also occur through the shallow Pn junction 18a, so light emission can of course be seen from the shallow Pn junction 18a region, but due to the low resistance of the zinc diffusion region 14, most of the current flows through the deep Pn junction 18a. 18b, and the substantial light emission flows through the deep Pn junction 18b provided in the center of the light emitting/receiving aperture 15.
It is conducted mainly in the area of

_{In this} example _, sufficiently thick n-In _{0.76 Ga 0.24} As _0.55 P _0.45
Despite the layer 12, the main part of the emission is due to the short carrier lifetime in the zinc diffusion region 14 and the thin n
Due to the shape area effect, ie, the high emission recombination rate due to the high injection carrier density, it has a high frequency response characteristic during light emission operation. Furthermore, since the light emitting/receiving aperture 15 is larger than the narrow light emitting region centered on the deep Pn junction 18b, it has an advantageous feature in coupling with an optical fiber, as will be described later.

On the other hand, the P-side electrode 16 is made negative and the shallow Pn junction 18a
If both _{the deep Pn junction 18b and the deep Pn junction 18b are biased in the opposite direction, the n-In 0.76 Ga 0.24 As 0.55 P 0.45 layer} 1
The electron-hole pairs generated in step 2 are taken out as photocurrent through the n-side electrode 17 and the p-side electrode 16 by the reverse bias electric field of the Pn junction. In this example, n-
In ₀ . ₇₆ Ga ₀ . ₂₄ As ₀ . ₅₅ P ₀ . ₄₅ The thickness of the layer 12 is large, several times the reciprocal of the effective attenuation constant for light at the wavelength of light emitted and received, and the light reception quantum efficiency is typically 60 to 80%. Compared to the 30 to 40% light-receiving quantum efficiency that can be obtained if a light-emitting diode is used, this value is considerably higher.

In addition, since the area of the shallow Pn junction 18a that occupies most of the light emitting/receiving aperture 15 in terms of area has little contribution to the light emitting operation, the n-
The In ₀ . ₇₆ Ga ₀ . ₂₄ As ₀ . ₅₅ P ₀ . ₄₅ layer 12 is non-doped and suppressed to a low carrier concentration convenient for light receiving operation.

During the light receiving operation, unlike during the light emitting operation, both the Pn junction regions under the light emitting/receiving aperture 15, that is, the shallow Pn junction 18a and the deep Pn junction 18b, work effectively. Therefore, when using this embodiment in combination with an optical fiber, it is sufficient to mainly consider the coupling efficiency during light emission operation. Even if the light cannot be completely focused on the center of the light-receiving aperture 15, a decrease in efficiency can be substantially prevented.

The dimensions of each part in this example should be optimized according to the characteristics of the optical fiber to be used, but the core diameter
A typical example of a device for 50 μm is an n-InP single crystal substrate 11 with a thickness of 70 μm, an n-
In _0.76 Ga _0.24 As _{0.55 P 0.45} Thickness of layer 12 is ₃ μm _{, P-}
The thickness of the InP layer 13 is 1 μm, the depth of the deep Pn junction 18b is 3.5 μm and the diameter is 20 μm, the diameter of the light emitting/receiving aperture 15 is 80 μm, the outer diameter of the device is 0.5 mm square, and the exposed Pn junction is protected when cutting out the device. In order to achieve this, mesa etching with a depth of approximately 5 μm and SiO coating for preventing surface reflection of light in the light emitting/receiving aperture 15 are applied.

In the above-described embodiments, a semiconductor with an n-type conductivity type was used as the substrate material, but it is of course possible to use a substrate of a p-type semiconductor and have a configuration in which the conductivity type is reversed. However, in this case, sulfur or the like would have to be used instead of the well-known P-type impurities such as zinc or cadmium, and an ion implantation method would have to be used as the introduction method. Regarding semiconductor materials, the above-mentioned InP-
Not limited to InGaAsP, but also GaAs depending on the required wavelength range.
- Group compound semiconductors such as -GaAlAs can also be used. When using GaAs-GaAlAs system, GaAs or Al should be used as the light emitting/receiving layer.
Using Ga _1-x Al _x As, (0<x<1), which has a small phase ratio, the upper and lower parts of the light-emitting and receiving layer have a high A1 composition ratio.
Ga _1-y Al _y As, (0<x<y<1) may be used. Further, the configurations of the electrodes and the light emitting/receiving aperture are not limited to the above embodiments. For example, there is no problem in a configuration in which a light emitting/receiving aperture is provided on the substrate side. However, it is opaque to the wavelength of emitted light, e.g.
When an element is fabricated using a substrate such as GaAs for the GaAs-GaAlAs system, it is necessary to remove the substrate in the light-emitting and light-receiving aperture area by etching or the like.

Finally, to summarize the advantages of the present invention, it can be manufactured in almost the same process as ordinary light emitting diodes, and high overall efficiency can be easily achieved in coupling with optical fibers through improvements in the electrode structure and light emitting layer structure. In addition, a light-emitting/light-receiving semiconductor element having excellent frequency response characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are a plan view and a side sectional view, respectively, of an embodiment based on the present invention. FIG. 3 is a sectional view of a conventional example. In the figure, 11...n-InP single crystal substrate, 12...n
_{−In 0.76 Ga 0.24 As 0.55 P 0.45 layer , 13 ... P - InP}
Layer, 14... Zinc diffusion region, 15... Light emitting/light receiving aperture, 16... P side electrode, 17... N side electrode, 18
a... Shallow Pn junction, 18b... Deep Pn junction.

Claims (1)

[Scope of utility model registration request] In a light-emitting/light-receiving semiconductor device that includes a double heterojunction structure composed of a - group compound semiconductor and has a light-emitting/light-receiving aperture on the top surface of the device, the thickness of the light-emitting/light-emitting layer having a narrower bandgap than the adjacent layer. is larger than the reciprocal of the attenuation constant of the light emitting/receiving layer for light having the wavelength of light emitting/receiving, and the main light emitting region is formed under an area narrower than the light emitting/receiving aperture at approximately the center of the light emitting/receiving aperture. It is characterized by having a locally deep Pn junction region formed by introducing impurities that reach the inside of the layer, and a shallow Pn junction region forming a main light receiving region under an area wider than the light emitting and receiving aperture. Semiconductor device that can emit light and receive light.