JP3138199B2 - Semiconductor waveguide type light receiving element and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor waveguide type light receiving device in which a pn junction at a cleavage end surface, which is a light incident end surface, is formed in a semiconductor layer having a larger band gap than a light absorption layer to reduce dark current. The present invention relates to an element and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional example of a semiconductor waveguide type light receiving element is shown in FIG.
Shown in In FIG. 4, reference numeral 301 denotes a semi-insulating InP substrate;
02 has a thickness of 0.6 μm and a band gap wavelength of 1.3 μm.
N-type InGaAsP layer 303 has a thickness of 0.4 μm
Type low carrier concentration InGaAs light absorbing layer, 304 is a 0.2 μm thick p-type InGaAs light absorbing layer, 305 is 0.6 μm thick p-type In with a band gap wavelength of 1.3 μm.
GaAsP layer, 306 is a 0.5 μm thick p-type InP
Layer, 307 is a 0.2 μm thick p-type InGaAs ohmic contact layer, 308 is an n-type ohmic electrode, 30
9 is a p-type ohmic electrode, and 310 is a non-reflective film made of silicon oxide formed on the cleavage plane. The above n-type InGa
AsP layer 302, n-type InGaAs light absorbing layer 303, p
The type InGaAs light absorbing layer 304, the p-type InGaAsP layer 305, the p-type InP layer 306, and the p-type InGaAs ohmic contact layer 307 are processed into a high-mesa shape having a length of 12 μm and a width of 4 μm. In this semiconductor waveguide type light receiving element, the boundary between the p-type semiconductor layer and the n-type semiconductor layer, that is, the pn junction is made of InG
(High-efficiency 50 GHz InGaAs multi-mode waveguide type light receiving element) formed in an aAs light absorption layer, IEE Raunal of
Quantum Electronics (IEEE Journal of
Quantum Electronics), Vol. 28, No. 12, 27
28, 1992)).

The principle of operation of the above-mentioned light receiving element is as follows. That is, light having a wavelength of 1.55 μm is applied to the non-reflection film 31.
The light enters from the cleavage end face through 0 and is guided in the optical waveguide constituted by 301 to 306. Meanwhile, the light is n-type In
GaAs light absorbing layer 303 and p-type InGaAs light absorbing layer 3
So-called photoelectric conversion is performed in which the light is absorbed at 04 and converted into electrons and holes. The electrons and holes generated by the photoelectric conversion travel to the n-type and p-type semiconductor layers, respectively, by the reverse bias voltage applied to the pn junction, and are taken out of the element as a signal current.

[0004]

In order to operate a semiconductor light receiving element with low noise, a current component other than a signal current, that is, a dark current must be reduced. Generally, when a dielectric such as an anti-reflection film is deposited on the pn junction, the dark current increases, and the increase increases as the band gap of the semiconductor layer on which the pn junction is formed becomes smaller. In fact, when silicon oxide was used as the non-reflective film in this semiconductor light receiving element, the dark current was 100 nA, which was much larger than the allowable value of 30 nA for suppressing noise. Therefore, in a conventional semiconductor light receiving element in which a pn junction is formed in a light absorbing layer, dark current cannot be reduced sufficiently, and low noise operation cannot be realized.

An object of the present invention is to solve the above-mentioned problem of the prior art that a dark current increases when a non-reflection film is formed on a cleavage end face, which is a light incident end face, and to obtain a semiconductor light receiving element having a low dark current. I do.

[0006]

SUMMARY OF THE INVENTION The above object is achieved by a first semiconductor layer, the second semiconductor layer is larger energy gap narrower refractive index than the first semiconductor layer, the energy gap than the second semiconductor layer wider refractive A third semiconductor layer having a small ratio is sequentially laminated to form a waveguide structure, and the waveguide structure has at least one light input end face, the first semiconductor layer and the second semiconductor layer following the light input end face, and A semiconductor layer adjacent to the second semiconductor layer and forming a part of the third semiconductor layer has a first conductivity type, and the third semiconductor layer not belonging to the semiconductor layer has a second conductivity type. 1 and a semiconductor layer adjacent to the first semiconductor layer and forming part of the second semiconductor layer adjacent to the first semiconductor layer and having the first conductivity type, following the first waveguide structure. The second semiconductor to which the semiconductor layer does not belong The semiconductor layer and the third semiconductor layer constituting the layer is achieved by providing a second waveguide structure having a second conductivity type.

It is another object of the present invention to provide a first semiconductor layer, a second semiconductor layer having a smaller energy gap and a larger refractive index than the first semiconductor layer, and a third semiconductor layer having a larger energy gap and a smaller refractive index than the second semiconductor layer. Semiconductor layers are sequentially stacked to form a waveguide structure, wherein the waveguide structure constitutes at least one light input end face and a part of the first semiconductor layer following the light input end face and the second semiconductor layer A semiconductor layer that is not adjacent to the first semiconductor layer has a first conductivity type, and the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer that do not belong to the semiconductor layer have a second conductivity type. Following the first waveguide structure, the first semiconductor layer and the semiconductor layer adjacent to the first semiconductor layer and constituting a part of the second semiconductor layer have a first conductivity type. And the second layer does not belong to the semiconductor layer. The semiconductor layer and the third semiconductor layer constituting a conductor layer is achieved by providing a second waveguide structure having a second conductivity type.

[0008] Further, the above object has at least a first object.
A semiconductor layer, a second semiconductor layer having a smaller energy gap and a larger refractive index than the first semiconductor layer, and a third semiconductor layer having a larger energy gap and a smaller refractive index than the second semiconductor layer were sequentially stacked. Forming a waveguide structure on a semiconductor substrate, wherein the waveguide structure has at least one optical input end face, following the optical input end face, a first semiconductor layer, a second semiconductor layer, and a second semiconductor layer A third semiconductor layer adjacent to the first semiconductor layer and forming a part of the third semiconductor layer has a first conductivity type, and a third semiconductor layer not belonging to the semiconductor layer is a second semiconductor layer.
Following the first waveguide structure having the first conductivity type, the first semiconductor layer and the semiconductor layer adjacent to the first semiconductor layer and forming a part of the second semiconductor layer have the first conductivity type, Removing the surface of the second waveguide structure having the second conductivity type, wherein the semiconductor layer forming the second semiconductor layer to which the semiconductor layer does not belong; Diffusing impurities for forming the conductivity type of the first and second waveguides to form a conductivity type structure of the first and second waveguides, and processing the waveguide structure having the conductivity type structure formed into a light receiving element This is achieved by having

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention is intended to suppress an increase in dark current due to the formation of a non-reflective film on a cleavage end face.
A pn junction is formed in the semiconductor layer having a larger band gap than the light absorption layer on the light incident end face of the semiconductor light receiving element.

Light incident from the cleavage end face through the non-reflective film is absorbed by the light absorbing layer in the optical waveguide, photoelectrically converted into electrons and holes, and then n-type and n-type are applied by the reverse bias voltage applied to the pn junction. It travels to the p-type semiconductor layer side and is taken out of the device. If the light absorbing layer has a pn junction, a dielectric of an antireflection film is deposited on the pn junction to increase dark current. And the increase is pn
It becomes larger as the band gap of the semiconductor layer where the junction is formed is smaller. Therefore, by forming a pn junction in a semiconductor layer having a larger band gap than the light absorption layer, a semiconductor light receiving element with reduced dark current can be obtained.

[0011]

Next, embodiments of the present invention and reference examples will be described with reference to the drawings. 1 is a diagram showing a reference example of a semiconductor waveguide type light receiving element that are related to the present invention, FIGS. 2 and 3 are views showing manufacturing steps of the first embodiment of the present invention.

Reference Example In FIG. 1 for explaining the structure of a reference example related to the present invention, 101 is a semi-insulating InP substrate, 102 is a first semiconductor layer having a thickness of 0.6 μm and a band gap wavelength of 1.3 μm.
m, an n-type InGaAsP layer; 103, a 0.6 μm-thick n-type low carrier concentration InGaAs light absorption layer as a second semiconductor layer; 104, a third semiconductor layer with a thickness of 0.2 μm and a bandgap wavelength of 1. 3 μm n-type low carrier concentration I
An nGaAsP layer 105 is a fourth semiconductor layer having a thickness of 0.1 mm.
P-type InGa with a band gap wavelength of 1.3 μm at 4 μm
An AsP layer 106 is a p-type InP layer having a thickness of 0.5 μm,
07 is a 0.2 μm thick p-type InGaAs ohmic contact layer, 108 is an n-type ohmic electrode, and 109 is a p-type ohmic electrode.
The type ohmic electrode 110 is a non-reflective film made of silicon oxide formed on the cleavage plane. The above n-type InGaAsP
Each layer from the layer 102 to the p-type InGaAs ohmic contact layer 107 is processed into a high mesa shape having a length of 12 μm and a width of 4 μm.

In the semiconductor waveguide type light receiving device having the above structure, the boundary between the p-type semiconductor layer and the n-type semiconductor layer, that is, the pn junction is formed at the n-type low carrier concentration InGaAsP layer 104.
And a p-type InGaAsP layer 105 having a bandgap wavelength of 1.3 μm. In fact, when silicon oxide is used as a non-reflective film in a semiconductor light receiving element manufactured using the present invention, the dark current becomes 1 nA, which is an allowable value for suppressing noise.
nA was fully satisfied.

[0014] In this reference example, an example of forming a pn junction InGaAsP layer bandgap wavelength 1.3 .mu.m, the same effect can form a pn junction on top of the InP layer can be expected . In the present embodiment, although an example of using the cleavage plane as a light incident end face, it can be expected a similar effect by using a surface formed by etching as the light incident end face.

First Embodiment In FIGS. 2 and 3 showing a structure and a manufacturing process of a semiconductor waveguide type photodetector according to a first embodiment of the present invention, reference numeral 201 denotes a semi-insulating InP substrate, and 202 denotes a 0.1 mm thick substrate. An n-type InGaAsP layer having a band gap wavelength of 1.3 μm and a thickness of 6 μm;
3 is an n-type low carrier concentration InGaAs having a thickness of 0.6 μm.
A light absorption layer 204, an n-type low carrier concentration InGaAsP layer having a thickness of 0.6 μm and a band gap wavelength of 1.3 μm,
Reference numeral 205 denotes an n-type low carrier concentration InP layer having a thickness of 0.7 μm near the light incident end face and 0.5 μm away from the light incident end face, 206 denotes a p-type diffusion region, 208
Is an n-type ohmic electrode, 209 is a p-type ohmic electrode,
210 is a non-reflective film made of silicon oxide formed on the cleavage plane. Each lamination from the n-type InGaAsP layer 202 to the n-type low carrier concentration InP layer is processed into a high mesa shape having a length of 12 μm and a width of 4 μm. In this semiconductor waveguide type light receiving element, the boundary between the p-type semiconductor layer and the n-type semiconductor layer, that is, the pn junction is formed in the light absorption layer 203 inside the waveguide, but the band gap wavelength 1 on the light incident surface. It is formed in a 0.3 μm InGaAsP layer 204.

The semiconductor waveguide type light receiving device according to the present embodiment is manufactured by the following steps. As shown in FIG. 2A, an n-type InG
aAsP layer 202, n-type low carrier concentration InGaAs light absorbing layer 203, n-type low carrier concentration InGaAsP layer 2
04 and 0.7 μm n-type low carrier concentration InP layer 2
2 is epitaxially grown in order, and as shown in FIG. 2B, a part of the n-type low carrier concentration InP layer 205 is etched by 0.2 μm, and the thickness at a position away from the light incident end face is reduced to 0.5 μm. To be. Next, FIG.
As shown in (c), Zn is diffused from the surface of the epitaxial layer, and a region from the surface to a depth of 1.2 μm is made to be a p-type conductivity type. As shown in FIG. 3A, the epitaxial layer is processed into a high mesa shape having a length of 12 μm and a width of 4 μm, and a part of the high mesa shape epitaxial layer is etched to form an n-type InGaAsP layer 20.
2 is exposed, an n-type ohmic electrode 208 is formed thereon, and a p-type ohmic electrode 209 is formed on a part of the n-type low carrier concentration InP layer 205. As shown in FIG. 3B, the epitaxial layer is cleaved to form a light incident end face, and the anti-reflection film 2 made of silicon oxide is formed on the light incident end face.
10 is deposited.

In the above manufacturing process, the n-type low carrier concentration InP layer 205 has a thickness of 0.7 μm near the light incident end face and a thickness of 0.5 μm at a location away from the light incident end face. Therefore, in the process, 1.2 from the surface
The pn junction formed at a depth of μm is located in the n-type low carrier concentration InGaAsP layer 204 near the light incident end face, and is located in the n-type low carrier concentration InGaAs light absorption layer 203 away from the light incident end face. positioned. As a result, at the light incident end face, a non-reflective film is deposited on the pn junction formed in the InGaAsP layer 204 having a larger band gap than the light absorbing layer 203, so that the dark current is reduced. In the semiconductor light-receiving element manufactured according to the present invention, when silicon oxide was used as the antireflection film, the dark current was 5 nA, which sufficiently satisfied the allowable value of 30 nA for suppressing noise.

In this embodiment, the p-type ohmic electrode 2
Although an example in which the InP layer 09 is formed on the n-type low carrier concentration InP layer 205 is shown, the same effect can be obtained even if the InP layer 205 is removed after the above steps and a p-type ohmic electrode is formed on the InGaAsP layer 204. Can be expected. Further, in this embodiment, an example in which the cleavage plane is used as the light incident end face has been described.
The same effect can be expected even if a surface formed by etching is used as the light incident end surface.

[0019]

Semiconductor waveguide type light receiving element according to the present invention as described above according to the present invention is the light incident end face of the semi-conductor waveguide type light receiving element, the pn junction in band gap than the light absorbing layer is larger semiconductor layer formed Accordingly, an increase in dark current due to the formation of a non-reflective film on the light incident end face is suppressed, and an effect is obtained that a low-noise semiconductor waveguide type light receiving element can be realized.

[Brief description of the drawings]

Participation of the semiconductor waveguide type light receiving element that are related to the present invention; FIG
It is a diagram showing a considered example.

FIG. 2 is a view showing a first embodiment of the present invention, wherein (a),
(B), (c) is a figure which shows a part of each manufacturing process.

FIGS. 3A and 3B are views showing a first embodiment of the present invention, wherein FIGS. 3A and 3B show a part of each manufacturing process. FIGS.

FIG. 4 is a view showing a structure of a conventional semiconductor waveguide type light receiving element.

[Explanation of symbols]

102 first semiconductor layer (n-type InGaAsP layer) 103 second semiconductor layer (n-type low carrier concentration InGa
As light absorbing layer) 104 Third semiconductor layer (n-type low carrier concentration InGa)
(AsP layer) 105 Fourth semiconductor layer (p-type InGaAsP layer)

Claims (3)

(57) [Claims] At least a first semiconductor layer and a second semiconductor layer having a smaller energy gap and a larger refractive index than the first semiconductor layer.
A semiconductor layer and a third semiconductor layer having a larger energy gap and a smaller refractive index than the second semiconductor layer are sequentially stacked to form a waveguide structure, wherein the waveguide structure has at least one light input end face, and Subsequent to the input end face, the first semiconductor layer, the second semiconductor layer, and a semiconductor layer adjacent to the second semiconductor layer and constituting a part of the third semiconductor layer have a first conductivity type and belong to the semiconductor layer. Not the third semiconductor layer is the second
A first waveguide structure having the following conductivity type, and a semiconductor layer adjacent to the first semiconductor layer and constituting a part of the second semiconductor layer, following the first waveguide structure. First
Semiconductor layer constituting the second semiconductor layer to which the semiconductor layer does not belong, and the third semiconductor layer,
A semiconductor waveguide type light receiving element comprising: a second waveguide structure having a second conductivity type. 2. At least a first semiconductor layer and a second semiconductor layer having a smaller energy gap and a larger refractive index than the first semiconductor layer.
A semiconductor layer and a third semiconductor layer having a larger energy gap and a smaller refractive index than the second semiconductor layer are sequentially stacked to form a waveguide structure, wherein the waveguide structure has at least one light input end face, and The semiconductor layer that forms part of the first semiconductor layer following the input end face and is not adjacent to the second semiconductor layer has a first conductivity type, and the first semiconductor layer does not belong to the semiconductor layer.
A semiconductor layer, the second semiconductor layer, and the third semiconductor layer, wherein a first waveguide structure having a second conductivity type;
Following the first waveguide structure, a first semiconductor layer and a semiconductor layer adjacent to the first semiconductor layer and constituting a part of the second semiconductor layer have a first conductivity type, and the semiconductor layer is A semiconductor waveguide type light receiving element in which the semiconductor layer and the third semiconductor layer that do not belong to the second semiconductor layer have a second waveguide structure having a second conductivity type. 3. A semiconductor layer having at least a first semiconductor layer, a second semiconductor layer having a narrower energy gap and a larger refractive index than the first semiconductor layer, and a third semiconductor layer having a wider energy gap and a smaller refractive index than the second semiconductor layer. Forming a sequentially laminated waveguide structure on a semiconductor substrate, wherein the waveguide structure has at least one light input end face, and a first semiconductor layer and a second semiconductor layer are provided following the light input end face. A semiconductor layer adjacent to the second semiconductor layer and constituting a part of the third semiconductor layer has a first conductivity type, and a third semiconductor layer not belonging to the semiconductor layer has a second conductivity type. Following the first waveguide structure, the first semiconductor layer and a semiconductor layer adjacent to the first semiconductor layer and constituting a part of the second semiconductor layer have a first conductivity type, and the semiconductor layer has a first conductivity type. Constituting the second semiconductor layer which does not belong The second conductor layer has a second conductivity type
Removing the surface of the waveguide structure of the second step;
Diffusing an impurity for forming the second conductivity type into the waveguide structure of (a), forming the conductivity type structures of the first and second waveguides, and processing the waveguide structure on which the conductivity type structure is formed. Producing a semiconductor waveguide type light receiving element.