JP2711055B2 - Semiconductor photodetector 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 photodetector having a structure capable of simultaneously reducing capacitance and parasitic resistance and capable of high-speed response, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A conventional general semiconductor photodetector has a low carrier concentration light absorbing layer 303 (FIG. 4) as shown in FIG. Are p-type conductive layers 30 above and below non-doped InGaAs).
4. An n-type conductive layer 302 is formed by arranging each of the layers (Satoshi Sakakibara et al., "High-speed GaInAs with reduced series resistance"
/ InP PIN photodiode ”Proceedings of the 1991 Spring Conference of the Japan Society of Applied Physics, 953 pages, 28p-F-
1). 307 is an n-electrode and 308 is a p-electrode.
In the semiconductor photodetector, the p-type conductive layer 304 and the n-type
A reverse bias voltage is applied between the semiconductor layer 302 and the conductive layer 302 to form a depletion layer in the non-doped light absorbing layer 303. This is for photoelectrically converting the signal light incident on the light absorbing layer.

Incidentally, the response speed of the semiconductor photodetector is determined by the CR time constant and the traveling time of the photoexcited carriers. In order to reduce the travel time of the photoexcited carriers, it is necessary to reduce the thickness of the light absorbing layer. However, in order to suppress an increase in capacitance C due to the thinning of the light absorbing layer, the area of the light absorbing layer is reduced. There must be.

[0004]

However, the above-mentioned p
Since it is necessary to form a p-type ohmic electrode on a part of the upper surface of the type conductive layer, the p-type ohmic electrode is
In a semiconductor photodetector provided with a type conductive layer, when the area of the light absorbing layer is reduced, the area of the p-type ohmic electrode is inevitably reduced. As a result, the ohmic resistance increases and the CR time constant increases. However, there was a problem that high-speed response could not be achieved after all.

An object of the present invention is to eliminate the relationship between the capacitance and the parasitic resistance in the prior art and to obtain a semiconductor photodetector capable of high-speed response.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide a semiconductor photodetector having a pn junction provided on a semiconductor substrate.
The pn junction is formed by forming a ridge with a side surface covered with a dielectric film, forming a cavity around the ridge side surface, and embedding the ridge with a semiconductor layer.

[0007]

According to the present invention, the pn junction is buried with a semiconductor layer by using a dielectric film mask formed on the side surface of the ridge-shaped pn junction and a part of the upper surface of the semiconductor substrate, thereby forming the periphery of the pn junction. A cavity is formed. In the present invention, since the pn junction is formed in a ridge shape, the area of the upper conductive layer can be set independently of the area of the light absorption layer. An ohmic electrode can be formed. In addition, since the n-type lower conductive layer and the p-type upper conductive layer are separated from each other by the cavity, a parasitic capacitance generated between the lower conductive layer and the upper conductive layer can be reduced, so that a semiconductor capable of high-speed response can be obtained. A light detector can be obtained.

[0008]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a structural diagram showing a first embodiment of a semiconductor photodetector according to the present invention, FIGS. 2 (a) to 2 (d) are diagrams showing manufacturing steps of the above embodiment, and FIG. 3 is a second embodiment of the present invention. FIG. 6 is a diagram showing a manufacturing process of the semiconductor photodetector showing the above. In FIG. 1, 10
1 is a semi-insulating InP substrate, 102 is an n-type InP lower conductive layer, 103 is a non-doped InGaAs light absorbing layer, 104
Is a p-type InP upper conductive layer, 105 is a dielectric mask, 10
6 is a cavity, 107 is an n-type ohmic electrode, and 108 is a p-type ohmic electrode. This semiconductor photodetector has a configuration of a waveguide type pin photodiode using the non-doped InGaAs light absorption layer 103 as a photoelectric conversion layer.

The manufacture of the semiconductor photodetector is shown in FIGS.
This is performed by the following steps shown in FIG. First, as shown in FIG. 2A, a film having a thickness of 0.2 mm is formed on a semi-insulating InP substrate 101.
μm n-type InP lower conductive layer 102 and a thickness of 0.5 μm
The non-doped InGaAs light absorption layer 103 is epitaxially grown in this order. Thereafter, the n-type InP lower conductive layer 102 and the non-doped InGaAs light absorbing layer 103 are etched in a ridge shape until the InP substrate 101 is exposed. Then, as shown in FIG. 2B, a dielectric film SiO ₂ 105 is deposited on the entire surface of the semiconductor layer formed in the ridge shape and the semi-insulating InP substrate 101, and the InP substrate near the ridge side surface and the lower portion of the ridge is formed. The dielectric film SiO ₂ 105 is removed by etching, as shown in FIG. Next, as shown in FIG. 2D, a p-type InP upper conductive layer 104 having a thickness of 2 μm is formed.
Select to grow. At this time, since the upper conductive layer 104 does not grow in the portion covered with the dielectric film SiO ₂ 105 near the ridge side surface and the lower portion of the ridge, a cavity 106 is formed in this portion. Thereafter, a part of the ridge is etched until the non-doped InGaAs light absorbing layer 103 is exposed, an n-type ohmic electrode 107 is formed on the exposed light absorbing layer 103, and a p-type ohmic electrode 107 is formed on the p-type InP upper conductive layer 104. By forming the type ohmic electrode 108, a semiconductor photodetector as shown in FIG. 1 is obtained.

[0010] separated by the above in the p-type InP upper conductive layer 104 epitaxial layer formed by selective growth, since the growth from the side as well as growth from the upper surface is promoted, the initial growth SiO ₂ film 105 When the growth is completed, the upper conductive layer 104 which has been
As shown in (d), the p-type InP upper conductive layer 104 has an extremely large area. Therefore, while keeping the area of the light absorption layer 103 small, the p-type ohmic electrode 108 having a large area
Can be formed. Further, since the cavity 106 separates the n-type InP lower conductive layer 102 from the p-type InP upper conductive layer 104, the parasitic capacitance generated between the two can be significantly reduced.

In a semiconductor photodetector manufactured by using the manufacturing method according to the present invention, a p-type ohmic electrode having a width of 10 μm is formed on a light absorption layer having a width of 1 μm. The parasitic capacitance can be reduced by a factor of one, and the parasitic capacitance can be reduced to a negligible level as compared with the element capacitance. The response speed can be 60 GHZ, which is about four times the performance of the conventional device.

A semiconductor photodetector according to a second embodiment of the present invention will be described with reference to FIGS. In FIG. 3, 201 is a semi-insulating InP substrate, and 202 is an n-type InP.
A P lower conductive layer, 203 is a non-doped InGaAs light absorbing layer, 204 is a p-type InP upper conductive layer, 205 is a dielectric mask, and 206 is a cavity. The semiconductor photodetector has a configuration of a waveguide type pin photodiode using the non-doped InGaAs light absorption layer 203 as a photoelectric conversion layer.

FIG. 3 shows a method of manufacturing the semiconductor photodetector.
Description will be made in accordance with the steps shown in (a) to (d). First, a 0.2 μm thick n
A type InP lower conductive layer 202 and a non-doped InGaAs light absorbing layer 203 having a thickness of 0.5 μm are epitaxially grown in this order, and the lower conductive layer 202 and the light absorbing layer 203 are semi-insulated as shown in FIG. Etching is performed in an inverted mesa ridge shape until the conductive substrate 201 is exposed. Next, as shown in FIG. 3B, a dielectric film SiO ₂ 205 is deposited on the entire surface of the semiconductor layer formed in the ridge shape and the semi-insulating InP substrate 201. Thereafter, an ion beam is irradiated from above the semiconductor substrate to form the dielectric film S
As shown in FIG. 3C, the iO ₂ 205 is removed by etching except for the side surface and the lower portion of the ridge. Here, since the ridge has an inverted mesa shape, the side surface of the ridge and the vicinity of the lower portion of the ridge become shadows of the ridge, and the ion beam does not reach the ridge. Therefore, the SiO ₂ film 205 near the ridge side surface and the lower portion of the ridge remains without being etched. Next, as shown in FIG. 3D, a p-type InP upper conductive layer 204 having a thickness of 2 μm is selectively grown, and the InP upper conductive layer 204 is formed on the side surface of the ridge and the SiO ₂ film portion near the lower portion of the ridge. Does not grow, a cavity 206 is formed in this portion. As in the first embodiment, a part of the ridge is etched until the non-doped InGaAs light absorbing layer 203 is exposed, an n-type ohmic electrode is formed on the surface of the absorbing layer 203, and the p-type InP upper conductive layer is formed. A p-type ohmic electrode is formed on 204 to obtain a semiconductor photodetector.

In the step of irradiating an ion beam from above the semiconductor substrate to remove the SiO ₂ film by etching, since the ridge is formed in an inverted mesa shape, an etching mask is not used, and the ridge side surface and the ridge lower portion are used. Since the SiO ₂ film 205 in the vicinity can be left, the manufacturing can be simplified as compared with the first embodiment, but it goes without saying that the same effect can be obtained.

In each of the above embodiments, an example in which a waveguide type photodetector is realized has been described. By applying the present invention to a surface incident type photodetector, a surface incident type photodetector capable of high-speed response can be obtained. Can be realized. In the above embodiment, the semiconductor material is I
Although an example is shown in which a material that lattice-matches with the nP substrate is used, a similar effect can be expected even if some or all of these materials do not lattice-match with InP. Also, an example in which the signal light wavelength is 1.55 μm has been described. However, by appropriately selecting a material, a semiconductor light detection device having the same effect as that of the present embodiment can be applied to signal light having a wavelength other than 1.55 μm. Vessel can be realized. Further, the present structure can be applied to another optical element such as a semiconductor laser or a semiconductor optical modulator.

[0016]

As described above, according to the semiconductor photodetector and the method of manufacturing the same according to the present invention, in a semiconductor photodetector having a pn junction provided on a semiconductor substrate, the pn junction has a side surface covered with a dielectric film. The ridge is formed in such a manner that a cavity is formed around the side surface of the ridge, and the ridge is buried with a semiconductor layer. At the same time, it is possible to realize a semiconductor photodetector which is reduced and has a small parasitic capacitance and is capable of high-speed response, and a manufacturing method thereof can be obtained.

[Brief description of the drawings]

FIG. 1 is a structural diagram showing a first embodiment of a semiconductor photodetector according to the present invention.

FIGS. 2 (a) to 2 (d) are diagrams respectively showing the manufacturing steps of the above embodiment.

FIG. 3 shows a semiconductor detector according to a second embodiment of the present invention;
(A)-(d) is a figure which shows a manufacturing process, respectively.

FIG. 4 is a schematic diagram showing a conventional semiconductor photodetector.

[Explanation of symbols]

 101, 201 Semiconductor substrate 102, 202 N-type lower conductive layer 103, 203 Light absorbing layer 104, 204 P-type upper conductive layer 105, 205 Dielectric film 106, 206 Cavity

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-47-23182 (JP, A) JP-A-50-140285 (JP, A) JP-A-2-166774 (JP, A)

Claims (2)

(57) [Claims] In a semiconductor photodetector having a pn junction provided on a semiconductor substrate, the pn junction is formed in a ridge shape with a side surface covered with a dielectric film, and a cavity is formed around the ridge side surface. A semiconductor photodetector having the ridge embedded in a semiconductor layer as described above. 2. A method for manufacturing a semiconductor photodetector having a pn junction provided on a semiconductor substrate, comprising: forming a semiconductor photodetector layer having a pn junction on the semiconductor substrate; Forming a ridge, depositing a dielectric film on the upper surface of the substrate near the side surface and lower portion of the ridge, and embedding the ridge by growing a semiconductor layer. Manufacturing method.