JPH09223805A - Semiconductor waveguide type light receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the structure of a light receiver and reduce its cost, by providing in it first to third semiconductor layers to form in a portion of the third semiconductor layer a diffusion region ranging from its surface to a predetermined depth place and having a different conduction type from the first to third semiconductor layers, and by exposing to the outside as its light incidence end the extending one-surfaces of both the diffusion region and the second semiconductor layer in its depth direction. SOLUTION: On a semi-insulation InP substrate 101, an n-type InGaAsP layer 102 of a first semiconductor layer, an n-type InGaAsP light absorbing layer 103 (absorption layer) of a second semiconductor layer with a longer absorption end wavelength and a larger refractivity than the first semiconductor layer, and an n-type InGaAsP layer 104 (n type layer) of a third semiconductor layer with a shorter absorption end wavelength and a smaller refractivity than the absorption layer 103 are provided. In the n-type layer 104, a Zn diffusion region 105 with a larger thickness than the n-type layer 104 is also diffused partially into the absorption layer 103. exposing the light incidence end of a light receiver to the outside. Also, n-and p-type electrodes 106, 107 are formed respectively on the n-type layer 104 and Zn diffusion region 105.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a semiconductor light receiving element having a structure, and particularly to a semiconductor waveguide type light receiver formed by impurity diffusion.

[0002]

2. Description of the Related Art FIG. 3 illustrates a conventional semiconductor waveguide type optical receiver. That is, 301 is a semi-insulating InP substrate, 30
2 is an n-type InGaAsP layer having a thickness of 0.6 μm and a bandgap wavelength of 1.3 μm, 303 is an n-type low carrier concentration InGaAs light absorption layer having a thickness of 0.6 μm, 304 is a thickness of 0.6 μm and a bandgap wavelength is 1 0.3 μm p-type In
GaAsP layer, 305 is 0.5 μm thick p-type InP
A layer, 306 is an n-type ohmic electrode, and 307 is a p-type ohmic electrode. (K.Kato et al., "A high-efficiency 50
GHz InGaAs ultimode waveguide photo detector '' IEEE
Lournal of Quantum Electronics Vol. 28, No. 12, 27
28, 1992). In the example of FIG. 3, a wavelength of 1.55
Light of μm is made incident from the cleaved end face, and each layer 302, 30
The inside of the optical waveguide consisting of 3, 304 and 305 is guided.
At this time, light is absorbed by the light absorption layer 303 and converted into electrons and holes, and so-called photoelectric conversion is performed. Electrons and holes generated by this photoelectric conversion are generated by the electrode 30.
6, 307, that is, in the electric field generated by the reverse bias voltage applied to the pn junction, they travel to the n-type and p-type semiconductor layer sides, respectively, and are taken out as a signal current to the outside of the element.

[0003]

When attempting to receive a high-frequency optical signal with the semiconductor waveguide type photodetector as described above, the CR time constant of the semiconductor waveguide type photodetector is made to sufficiently respond to the frequency of the signal. Needs to be small enough. Specifically, it is necessary to reduce the capacitance C. 5 as an example
When receiving a 5 GHz optical signal in the 0Ω system, 0.6
The capacity must be less than or equal to PF. now,
In the case of an ordinary semiconductor waveguide type light receiving element in which the thickness of the absorption layer 303 is about 1 μm, the capacitance is 0.6 PF as described above.
In order to make it below, it is necessary to suppress the pn junction area to 4000 μm ² or less. Therefore, as shown in FIG. 3, the semiconductor layer is dug down to the pn junction surface or less so that it is processed into a so-called high-mesa shape to remove excess capacitance, and 4000 μm is removed.
The area is less than or equal to m ² . Therefore, manufacturing of a conventional semiconductor waveguide type optical receiver requires high-mesa processing, high-mesa electrode formation, and the like, and requires a technique with a large number of steps and high difficulty.

In view of the above problems, it is an object of the present invention to provide a semiconductor waveguide type photodetector having a simple structure and a low cost, not a structure related to a high mesa having a large number of steps and a high degree of difficulty.

[0005]

The present invention which achieves the above-mentioned object is defined as the following invention. (1) a first semiconductor layer, and a second semiconductor layer having a longer light absorption edge wavelength and a larger refractive index than the first semiconductor layer,
In a semiconductor waveguide type optical receiver having a third semiconductor layer having a shorter absorption edge wavelength of light and a smaller refractive index than the second semiconductor layer, a part of the third semiconductor layer has a predetermined depth from the surface. A diffusion region having a conductivity type different from that of the other regions is formed over the entire surface, and the diffusion region and one surface of the second semiconductor layer are exposed as a light incident end in the depth direction. (2) A semiconductor substrate, a second semiconductor layer having a longer absorption edge wavelength of light and a larger refractive index than the semiconductor substrate, and the second semiconductor layer.
A third semiconductor layer having a shorter absorption edge wavelength of light and a smaller refractive index than that of the semiconductor layer, a part of the third semiconductor layer is covered with a third semiconductor layer over a predetermined depth from the surface. A diffusion region having a conductivity type different from that of the region is formed, and the diffusion region and one surface of the second semiconductor layer are exposed as a light incident end in the depth direction. (3) In the above (1) or (2), the diffusion region is formed so as to gradually expand from the light incident end along the traveling direction of light. (4) In the above (1) or (2), the diffusion depth from the surface of the third semiconductor layer reaches a part of the second semiconductor layer.

Since the slab type optical waveguide is formed by the pn junction formed by the impurity diffusion, the junction capacitance can be reduced and the manufacturing is simple and the cost is low.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the invention will now be described with reference to FIGS. The junction capacitance can be reduced by limiting the area of the pn junction by diffusing impurities.
The present invention is based on this idea to obtain a conductive path type optical receiver. In FIG. 1, 101 is a semi-insulating InP substrate, 102 is a thickness of 2 μm, and the bandgap wavelength is 1.2 μm.
m is an n-type InGaAsP layer, 103 is a 3 μm thick n-type low carrier concentration InG having a band gap wavelength of 1.4 μm.
aAsP light absorption layer 104, n-type low carrier concentration InGaAsP having a thickness of 2 μm and a band gap wavelength of 1.2 μm
It is a layer.

A Zn diffusion region 105 is partially formed in this layer 104. This region is formed in an area where the junction capacitance is a certain value or less, for example, 4000 μm ² or less, and the junction capacitance is reduced. In this case, Zn diffusion can be easily performed by limiting the diffusion portion.
Further, the Zn diffusion region 105 is, for example, 2 at the light incident end.
0 μm, depth 100 μm, depth 50 μm,
The light is gradually expanded along the traveling direction of the light according to the spread of the guided light. This is because the light conversion efficiency becomes extremely good. Further, the depth of the Zn diffusion region 105 is the surface (upper surface).
Therefore, when the thickness of the n-type layer 104 is 2 μm or more, the depth is such that it partially diffuses into the absorption layer 103. There is a suitable value for the depth of this diffusion, and if the electrons and holes generated by light absorption are too deep, the speed increases and the response becomes poor, and if it is too shallow, the distance to the junction surface is too long. It is decided in consideration. In manufacturing, since it is a so-called slab type waveguide in which light is incident from the end face of the diffusion region, the substrate 101 including the layers 102, 103 and 104 is cleaved or etched. The state of the end face, particularly the end face of the absorption layer 103 and the Zn diffusion region 105, is good for light incidence. Although Zn diffusion has been described above, diffusion of other substances such as Be diffusion can also be applied. In the figure, 106 is an n-type ohmic electrode and 107 is a p-type ohmic electrode.

FIG. 2 shows the structure of the second example. In FIG. 2, 201 is a semi-insulating InP substrate, and 203 is a thickness of 3 μm.
And an n-type low carrier concentration InGaAsP light absorption layer having a bandgap wavelength of 1.4 μm, and an n-type low carrier concentration InGa 204 having a bandgap wavelength of 1.2 μm and a thickness of 2 μm.
AsP layer, 205 has a depth of 3 μm and a length of 10 as in FIG.
The width of the Zn diffusion region of 0 μm is 20 μm at the light incident end, and gradually widens to 50 μm along the light traveling direction. 206 is an n-type ohmic electrode and 207 is a p-type ohmic electrode.

The semiconductor waveguide type light receiving element shown in FIGS. 1 and 2 has an optical waveguide structure in which the absorption layers 103 and 203 are used as core layers, and the diffusion region is widened according to the spread of incident light. All the light of 3 μm is absorbed in the pn junction region and can be extracted as an optical signal. By the way,
The pn junction area in this example is equal to the Zn diffusion area and is 3500
It becomes μm ² and it becomes possible to sufficiently receive an optical signal of about 5 GHz. In this example, the same effect can be expected even if a semi-insulating or conductive substrate is used as the semiconductor substrate. Further, the same effect can be expected by forming one electrode on the back surface of the semiconductor substrate.

[0011]

As described above, according to the present invention,
Since the pn junction of the semiconductor waveguide type light receiving element is formed by impurity diffusion, the junction capacitance can be reduced without high mesa processing, and a semiconductor waveguide type optical receiver having a simple structure and low cost can be realized. You can

[Brief description of drawings]

FIG. 1 is a structural diagram showing an example of an embodiment of the present invention.

FIG. 2 is a structural diagram showing another example of the embodiment of the present invention.

FIG. 3 is a structural view of a conventional example.

[Explanation of symbols]

 101, 201 InP substrate 102 n-type InGaAsP layer 103, 203 Light absorption layer 104, 204 n-type InGaAsP layer 105, 205 Diffusion region

Claims (4)

[Claims] 1. A first semiconductor layer, a second semiconductor layer having a longer light absorption edge wavelength than that of the first semiconductor layer and a large refractive index, and a light absorption edge wavelength of light from this second semiconductor layer. A third semiconductor layer having a short length and a small refractive index, and a diffusion region having a conductivity type different from other regions over a predetermined depth from the surface in a part of the third semiconductor layer. And the one surface of the second semiconductor layer is exposed as a light incident end in the depth direction. 2. A semiconductor substrate, a second semiconductor layer having a longer absorption edge wavelength of light and a larger refractive index than this semiconductor substrate, and a shorter absorption edge wavelength of light and a smaller refractive index than this second semiconductor layer. In a semiconductor waveguide type optical receiver having a third semiconductor layer, a diffusion region having a conductivity type different from that of other regions is formed in a part of the third semiconductor layer from a surface to a predetermined depth. A semiconductor waveguide type optical receiver characterized in that a region and one surface of the second semiconductor layer are exposed as a light incident end in the depth direction. 3. The semiconductor waveguide type photodetector according to claim 1, wherein the diffusion region is formed so as to gradually expand from the light incident end along the light traveling direction. 4. The diffusion depth from the surface of the third semiconductor layer is
The semiconductor waveguide type optical receiver according to claim 1 or 2, which reaches a part of the second semiconductor layer.