JPS63199467A - Photodiode - Google Patents

Abstract

PURPOSE:To obtain a photodiode which is of planar structure and easily formed in low capacity, in its turn, excellent in high-speed performance, by making at least one part of a second-conductivity type region, which is unconcerned with incidence of light, advance to a semiinsulating substrate. CONSTITUTION:First semiconductor layers 12 to 14 which show a first conductivity type are formed on one main surface of a semi-insulating substrate 10, and certain regions of the first semiconductor layers 12 to 14 are selectively converted into second-conductivity type regions 15 and 16 so as to form p-n junction. Signals of light made incident to this p-n junction are converted into electrical signals. In such a photodiode, at least one part of said second- conductivity type region 16, which is unconcerned with incidence of light, is made to advance to the semiinsulating substrate 10. For example, after the n<+>-InP layer 12, n-InGaAs layer 13, and n-InP layer 14 are formed on the iron- doped semiinsulating InP substrate 10, the Zn selective diffusion p<+> region 15 is formed so as to advance to the n<->-InGaAs layer 13. Further, the deep p<+> region 16 is formed so as to advance to the semi-insulating substrate 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a photodiode used in reverse bias operation, and particularly to a photodiode that is excellent in reducing capacitance.

(Prior art and its problems) Avalanche photodiodes, which are used near avalanche breakdown and utilize internal multiplication effects as semiconductor photodetectors, and photodiodes, which do not have multiplication effects but are used at low bias, are well known. Research and development is progressing on it as a light-receiving element for optical communication systems, along with semiconductor lasers and light-emitting diodes, which are light sources.

In current optical communication systems, the low loss region of optical fiber, which is the optical transmission medium, is in the 1.3 to 1.6 gm wavelength range, and correspondingly, the low loss region of optical fiber, which is the optical transmission medium, is in the wavelength range of 1.3 to 1.6 gm. Optical transmission has become mainstream. The light source in this wavelength range is InGaA, which is lattice matched to InP.
A laser diode using an sP mixed crystal, and a photodiode or an avalanche photodiode using an InGaAsP ternary mixed crystal material lattice-matched to InP, which can cover the entire wavelength range of the InGaAsP mixed crystal, are used as a photodetector. ode or central. Naturally, considering economic efficiency, the possibility of long-distance and large-capacity is being pursued, and the development of ultra-high-speed photodetectors is awaited.

Avalanche photodiodes, which are currently being put into practical use or are being put into practical use, can be expected to have high sensitivity because they utilize internal multiplication. It is characterized by deterioration. Therefore,
Research and development of photodiodes as photodetectors aimed at ultra-high speed is being carried out, and one example is reported in, for example, Electronics Letters, Vol. 21, pp. 262-263. FIG. 2 is a cross-sectional view schematically showing the photodiode. In this photodiode, its basic form is obtained by crystal-growing an n-InGaAs layer 13 on an n+-I'nP substrate 11 and forming a p+-InGaAs layer 15 on its main surface using an impurity diffusion method. . The feature here is that the n-InGaAs layer 13 is finally made thin to about 1.5 pm, and in this region, by shortening the travel time of photoexcited carriers when a reverse bias is applied,
A high-speed modulation characteristic with a dB drop cutoff frequency of approximately 20 GHz has been obtained. Such high speed is due to n-InG
This is because by making the aAs layer 13 thinner, the transit time of carriers generated by photoexcitation is shortened, and by forming it into a mesa structure as shown in FIG. 2, the capacitance of the pn junction is reduced.

However, such a mesa structure is not reliable.

A high-speed photodiode with a planar structure is desired, although this structure is not necessarily desirable from the standpoint of practicality and mounting. An example of a photodiode with a planar structure is the structure shown in FIG.

In the photodiode shown in the figure, a crystal having an n''-InP layer 12, an n--InGaAs light absorption layer 13, and an n-1nP cap layer 14 on an n→-InP substrate 11 is used to selectively form a p (region). After forming the insulation ai7.
It is composed of an n-type electrode 18 and an n-type electrode 19.

The feature here is that it has a planar structure, which has many advantages such as ease of handling and high reliability.
It is necessary to provide a region having a large area as a mold electrode for contact with a lead wire for bias application, which poses a problem in that it is difficult to reduce the capacitance.

Therefore, the purpose of the present invention is to improve the structure by devising the structure.
The object of the present invention is to provide a photodiode that has a planar structure, can easily reduce the capacitance, and has excellent high-speed performance.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a means for solving the above-mentioned problems by forming a first conductivity type on the -1 surface of a semi-insulating substrate.
A pn junction is formed by selectively converting a region of the first semiconductor layer into a region of a second conductivity type, and a light signal incident on the pn junction is The photodiode converts into an electric signal, and is characterized in that at least a portion of the second conductivity type region that does not participate in the incidence of light reaches the semi-insulating substrate.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing an embodiment of the photodiode of the present invention. In the manufacturing of this embodiment, first, an n''- layer with an i thickness of 0.51 Im and an impurity concentration of 5 x 10''cn-3 is deposited on an iron-doped semi-insulating InP substrate 10 having an (ioo) plane by, for example, vapor phase growth. After growing the 1nP layer 12, the film thickness is 1.5 μm and the impurity concentration is I x 10” -
3 n-InGaAs layer 13 is grown. Next, film thickness 14+m, impurity concentration 8X 10" an-3 n-I
An nP layer 14 is formed. After forming, for example, 5i02Jl on the surface of the wafer thus obtained, one region is selectively removed by a photoresist process. Next, using this 5i02 film as a mask for impurity diffusion, for example, Zn5P' The wafer is placed in a closed tube that is evacuated to a high vacuum using 2 as a diffusion source, and after sealing, heat treatment is performed at around 520° C. for several minutes to form a p+ region 5 for selective diffusion of Zn. The tip of region 15 is n--InGaA
The heat treatment time is adjusted so that the s-layer 13 is reached. Next, after forming 5102M again, a region of 5i02 overlapping with a region of the p10 region 15 is removed by the photoresist process as above, and then, for example, Zn is diffused using 5i02 as a diffusion mask in the same manner as above. Do this.

If the above wafer is used here, for example, 520°
A deep p+ region 16 is formed so as to reach the semi-insulating substrate 10 by heat treatment with C for about 45 minutes. For example, a Si3N4 film 1 is applied to the wafer that has undergone such a process as an insulating film.
form 7. In this insulating film, an electrode extraction window is provided on the deep p region 16 by a photoresist alignment process, and an n-type electrode 18 is provided.

Finally, in order to take out the n-type electrode, after selectively removing the n-InP layer 14 and the n-I nGaAs layer 13 in the region close to the p-type region 15 forming the light-receiving region,
The photodiode of this example is obtained by providing an n-type electrode 19 on the ``-1nP12.

As mentioned above, the following characteristics were obtained from the device obtained according to one embodiment of the present invention. That is, the effective p+diffusion diameter involved in photoelectric conversion (this corresponds to the effective diameter of the P10 region 15 that does not overlap with the deep P10 region 16) is 25 pmφ
The element capacitance under bias is 0.08 pF.
High-speed performance was achieved, with a cut-off frequency of 3 dB drop of 20 GHz or more for optical pulses with a wavelength of 1.3 μm. In the embodiment of FIG.
Compared to the conventional example in which the pn junction capacitance under the electrode region in the planar structure or the parasitic capacitance through the insulating film greatly limits the element capacitance, the pn junction region under the electrode formation region is a semi-insulating substrate. By contacting each other, it is possible to significantly reduce the capacitance and achieve a lower capacitance, and furthermore, due to this lower capacitance, the response to the optical pulse is reduced by the transit time of the photoexcited carriers, that is, n-I nG
It can be understood that high-speed performance close to the limit characteristic limited only by the transit time in the aAs layer 13 was obtained.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to provide a photodiode which has a planar structure, can easily reduce the capacitance, and has excellent high-speed performance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a photodiode according to the present invention, FIG. 2 is a sectional view showing a conventional high-speed photodiode, and FIG. 3 is a sectional view showing a conventional planar photodiode. 10... Semi-insulating InP substrate, 11... n''-InP
Substrate, 12...n+I nP layer, 13...n--
InGaAs scrap, 14-・-n-InP layer, 15-p+
Territory region 16--deep p region, 17--insulating film, 1
8...n-type electrode, 19...n-type electrode.

Claims (1)

[Claims] A first semiconductor layer exhibiting a first conductivity type is provided on one main surface of a semi-insulating substrate, and a region of the first semiconductor layer is selectively converted to a region of a second conductivity type. In a photodiode that converts a light signal incident on the pn junction into an electrical signal, at least a portion of the second conductivity type region not involved in the incidence of light is formed in the semi-insulating region. A photodiode characterized by reaching down to the conductive substrate.