JPH01140678A - Photodetector - Google Patents

Abstract

PURPOSE:To provide a photodetector operable at high speed and to facilitate application thereof in an photoelectronic integrated circuit, by inverting conductivity type of first and second light absorbing layers so that p-n junctions are formed vertically to a substrate. CONSTITUTION:A linear groove is formed in a semi-insulating semiconductor substrate 13. First and second n-type light absorbing layers 14, 15 are formed by crystal growth such that they border the groove vertically and that they have flat surfaces. A p-type dopant is diffused in a part of the first and second light absorbing layers 14, 15 so that p-n junctions 20, 21 are formed along the groove. Reverse bias is applied to the P-N junctions 20, 21 of the first and second light absorbing layers 14, 15, so that depletion layers are extended into optical guides and the first and second light absorbing layers 14, 15 are caused to function as a p-i-n photodiode. Namely, the conductivity type of the first and second light absorbing layers 14, 15 are inverted so that p-n junctions are formed along first and second optical guides 16, 17 vertically to the substrate 13. A photodetector thus constructed is allowed to operate at high speed and can be integrated easily with other electronic elements.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides wavelength selection 11 (W) for incident light of two or more wavelengths.
This invention relates to the structure of a light-receiving element having a high speed and can be used as a light-receiving element that can be easily applied to optoelectronic integrated circuits.

Prior Art A structure including a receiver having a wavelength selection function for incident light of two or more wavelengths is disclosed in Japanese Patent Application No. 151, for example.
There is a structure shown in FIG. 5 shown in Japanese Patent No. 578. In this structure, n-[nP second emitter 2, p-(nGaAsP (l wavelength λg=1.1
7zm) Second base 3, n-1nGaAsP (composition wavelength λg = 1.171 m) First emitter and second collector 4, p-InGaAsP (g composition wavelength λg = 1.3 μm)
First base 5, n -1tlP n cladding and first collector 6, rnGaAsP (, [wavelength λg=1.171
m) active layer 7 and I) -r n P p cladding 8 are laminated. Among them, P-crat 8, active layer 7,
The n-cladding 6 constitutes a light emitting element 9. Also, the first
The collector 6, the first base 5, and the first emitter 4 constitute the first phototransistor 1O, and the second collector 4, the second base 3, and the second emitter 2 constitute the second phototransistor 1.
1.

Here, although the function of the light emitting element 9 is not directly related to the present invention, the first and second phototransistors 1O1li function as a light receiving element having a wavelength selection function for incident light of two or more wavelengths. . The first and second phototransistors have a wide band gap emitter structure, the longest wavelength at which light can be received is determined by the band gap of the base, and the shortest wavelength is determined by the band gap of the emitter. That is, the second phototransistor selectively receives light with a wavelength of 0.9-1.1 μrn, and the first phototransistor selectively receives light with a wavelength of 1°1-1.3 μm. . Therefore, the incident light 12
When light with a wavelength of 1.0 μm and 1.2 μm is incident simultaneously, the light with a wavelength of 1.071 m is converted into a current by the second phototransistor, 2μm light is the first
The phototransistor converts the current into a current.

Problems to be Solved by the Invention Since the light receiving element shown in FIG. 5 performs photoelectric conversion using a phototransistor, it has the advantage of having an amplification function, but it is difficult to increase the response speed. Furthermore, since it has a vertical integrated structure, it is not easy to apply it to, for example, an optoelectronic integrated circuit that also integrates electronic elements.

Means for Solving the Problems In order to solve the above problems, the present invention provides a semi-insulating semiconductor substrate, and a semiconductor thin film formed on a partial region of the substrate and having a higher refractive index than the substrate. a first light absorption layer including a first optical waveguide; a second light absorption layer made of a t-conductor thin film having a band gap smaller than that of the light absorption layer and including a second optical waveguide, the first and second optical waveguides being optically coupled. and perpendicular to the substrate along the first and second optical waveguides l) -n
The light-receiving element has a structure in which the conductivity types of the first and second light absorption layers are reversed so that a junction is formed.Function The light-receiving element of the present invention is made of, for example, a semi-insulating semiconductor. Grooves were formed in stripes on the substrate, and the first and second light-absorbing layers, both of n-type, were crystal-grown so that their surfaces were flat, with boundaries perpendicular to the grooves. After that, p-type impurities are diffused into parts of the first and second light absorption layers to form p-n junctions along the grooves. Here, the first and second light absorption layers formed on the grooves become first and second optical waveguides, respectively. By applying a reverse bias to the p-n junction of the first and second light absorption layers and expanding the depletion layer into the optical waveguide, the light absorption layer becomes p-1-n.
It can function as a photodiode.

In this light receiving element, the composition wavelength λ2 of the second light absorption layer is the first wavelength.
Since the composition length of the light-absorbing layer is larger than 1, the first light-absorbing layer absorbs light with a wavelength of 1 or less, and the second light-absorbing layer absorbs light with a wavelength of 1 or more and less than λ2. be done. That is, wavelength selection is possible. Furthermore, since the photoelectric conversion is performed by using a l)-i-n photodiode whose p-n junction has a very small area, high-speed operation is possible.

Furthermore, since this photodetector has a Brener structure, it is easy to manufacture and can be easily integrated with other electronic devices. It is a diagram.

Semi-insulating [nP substrate 13 with stripe-like grooves formed
A first light absorption layer 14 made of n-InGaAsP (
composition wavelength λg = 1.4 μm) and n-Inc; aAs
A second light absorption layer 15 made of the above is crystal-grown, and the first light absorption layer 14 on the groove serves as a first optical waveguide 16. On the other hand, FIG. 2 is a sectional view taken along the line AA' shown in FIG. 1, and the second light absorption layer 15 on the groove serves as the second optical waveguide 17. Further, a part of the first and second light absorption layers 14.15 is made of a first p-layer film in which Zn or the like is diffused.
A type inversion region 18 and a second p-type inversion region 19 are formed, a first p-n junction 20 is formed along the first optical waveguide 16, and a second p-n junction 21 is formed along the second optical waveguide 16. It is formed along the optical waveguide 17 of. Furthermore, the first and second
p4'! on the p-type layer transfer region 18.19. 'ITj, polar 2
2. An n-side electrode 23 is provided on the other first and second light absorption layers 14 and 15.

Since the first optical waveguide 16 is transparent to light having a wavelength of 1.41 tm or more, for example, the incident light 24 has a wavelength of 1.3 tm.
μm and 1. When light of 5 μm is simultaneously incident, the wavelength is 1.
Only 3 μm light is absorbed by the first optical waveguide 16. On the other hand, light with a wavelength of 1.5 μm passes through the first optical waveguide 16, enters the second optical waveguide 17, and is absorbed there. At this time, if a reverse bias is applied between the n-side electrode 22 and the n-side electrode 23 provided on the light absorption layer, a depletion layer is expanded within the first and second optical waveguides 16 and 17. , the absorbed incident light 24 is converted into an electric current. The p-n junction required for this photodetector is only a portion with a length of approximately 57 tm along the optical waveguide, and the separation shown in Figure 1 is done to prevent additional p-n junctions from occurring. Electrical isolation is provided by grooves 25. This deviation is because the area of the [)-n junction is the thickness of the optical waveguide (for example, about IBtn) x 5 μm,
The area is much smaller than that of the p-11 junction of a conventional light-receiving element, and the junction capacitance is also very small. For example, the carrier concentration of the light absorption layer is 5 × l Q I'l, and the applied voltage is 1
If it is 0V, the junction capacitance is 3. 2X 10-”F, and the value of the load resistance is 101 (Ω), and the cutoff frequency is 3dB
t is 50 GHz.

Furthermore, since the present photodetector has a so-called burener structure with a flat surface, it can be easily applied to optoelectronic S product circuits. In order to integrate electronic devices, for example, a portion of the light absorption layer other than the optical waveguide may be used as a channel layer of an FET. Alternatively, this part can be used as a collector layer, and a p-InGaAsP base layer and an n-Tn
It is also possible to construct a heterojunction bipolar transistor by stacking P emitter layers.

Next, a sectional view of the light receiving element according to the second embodiment of the present invention is shown in the third embodiment.
As shown in the figure. Figure 3 is a sectional view of the same part as Figure 2;
Components having the same functions as those in FIG. 2 are given the same numbers. This embodiment differs from the first embodiment only in that the first and second optical waveguides are ridge-shaped. Although a ridge-type optical waveguide has the disadvantage that the surface is no longer a brainer, it has the advantage that the first and second light absorption layers can be crystal-grown on a flat substrate ball.

A cross-sectional view of a light receiving element according to a third embodiment of the present invention is shown in FIG. FIG. 4 is also a sectional view of the same part as FIG. 2, and the same numbers are given to parts having the same functions as FIG. 2.

This embodiment differs from the first embodiment only in that a cladding layer 26 is laminated on the light absorption layer. Although there is a drawback that the area of the pn junction increases when the cladding N26 is stacked, there is an advantage that the waveguide loss of the first light absorption layer is reduced.

In the above description of the embodiments, it is assumed that the material constituting the light receiving element of the present invention is InGaAs/InP, but [nGaAlAs/lnP, AlGaAs/G
It goes without saying that other semiconductor materials such as aAs-based materials may also be used.

Effects of the Invention As described above, by using the present invention, it is possible to easily construct a light receiving element having a wavelength selection function for incident light of two or more wavelengths. This photodetector is capable of high-speed operation, and
Applications such as integration with other electronic elements to form an optoelectronic integrated circuit are also easy.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a light receiving element according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA' in FIG. 1, and FIGS. 5 is a sectional view of a conventional light receiving element. 13... Substrate, 14... First light absorption layer, 15...
-Second light absorption layer, 16...first optical waveguide, 17.
...Second optical waveguide, 20...First ρ-n junction, 2
I...Second p-n junction. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 1! 4 1st I? Light absorption 1 2nd @ 2nd light absorption layer

Claims (1)

[Claims] a semi-insulating semiconductor substrate; a first light absorption layer formed on a partial region of the substrate and made of a semiconductor thin film having a higher refractive index than the substrate and including a first optical waveguide; a second light guide formed on a region other than the region where the first light absorption layer is formed, in contact with the first light absorption layer, and made of a semiconductor thin film having a band gap smaller than that of the first light absorption layer; a second light absorption layer including a waveguide, the first and second optical waveguides being optically coupled;
and the conductivity types of the first and second light absorption layers are reversed so that a pn junction is formed perpendicular to the substrate along the first and second optical waveguides. A light-receiving element.