JPH0362977A - Long wavelength avalanche photodiode - Google Patents

Abstract

PURPOSE:To eliminate the need for a high-frequency filter circuit and obtain an APD with improved high-frequency characteristics by making electrons, which are generated optically in a light absorbing layer by combining an inverse layer type NMOS transistor and APD then increased in an increase layer, to be n-type channel carriers. CONSTITUTION:An NMOS transistor is formed being based on a P-InGaAsP. Namely, an n<+>InGaAsP region 13, a drain electrode 14, and a source electrode 15 are formed. Also, a gate electrode 12 enabling light to pass through uses a transparent electrode such as InxOy and SnxOy. A gate 10 is a surface ohmic electrode 10 which is in ohmic contact with the gate electrode 12, thus forming an n-type channel 16 by gate voltage. Light entering from the gate electrode 12 to be applied with gate voltage is absorbed by a P<->-InGaAs/P<->-InGaAsP light-absorbing layer 3b and generates electrons, which are placed on a depletion layer electric field produced by gate voltage, and electrons increased by a P- InGaAsP increase layer 5b become the carrier of an n-type channel 16 and are output from the electrode of the drain electrode 14 and the source electrode 15.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to avalanche photodiodes (hereinafter referred to as AP).
AP
This relates to an APD structure in which the output of D is not affected by the bias circuit and depletion layer capacitance.

[Conventional technology]

FIG. 2 is a cross-sectional view showing the structure of a conventional long wavelength APD. In the figure, (la) is an n”-InP substrate, (2
a) is n-InP buffer no (3a) is n--In
QiAs or C or less/), InGaA
s P light absorption layer, (4a> is n--InGaAsP FA to improve frequency response, (5a) is n-InP
Multiplier layer, (6) is n-InP guard ring/in, (7
) is a protective insulating film, (8) is a guard ring region formed by Be ion implantation, (9) is a Cd diffusion region, σQ is a surface ohmic IIE electrode, and (b) is a back ohmic electrode.

Next, a method of manufacturing a conventional long wavelength APD structure will be explained. n
” -1 nP substrate (la), n--1 nP buffer layer (2a), n InGaAs/InGaA
sP light absorption layer (3a), n-InGaAsP layer (4a)
, n-InP multiplication m (5a), and n-InP guard ring layer (6) are epitaxially grown in sequence.

After that, by Be ion implantation and annealing, a guard ring region (8) with a P+n graded junction with a small concentration gradient is formed.
and a Cd diffusion region (9) forming a Pn step junction. Finally, the front drunken ohmic electrode scream and the back drunkenness ohmic Wla
an and a long wavelength APD structure is fabricated.

Next, the operating principle of the long wavelength APD structure will be explained. The long-wavelength light enters the light-receiving surface surrounded by the ring-shaped 100-ohmic electrode CIO, and passes through the protective insulating film (7) and the Cd diffusion region (
9), n-↓InP multiplied skin (5a), n--InGaA
It efficiently passes through each layer of the sP layer (4a), and all n-1n
It is absorbed by GaAs/InGaAsP light absorption/1i (3a) and generates carrier pairs by light excitation. Between the front ohmic electrode αQ1 and the back ohmic 'lIt pole (6), avalanche always occurs in the Ca diffusion region (the multiplication region which is n--InP multiplication m(5a) below 97). A nearly reverse voltage is applied, and nInGaAs /I nGaAsP light absorption I
The depletion layer extends sufficiently to I(3a). I-1nG
Carrier pairs generated at the aAs/1 nGaAsP optical yield (3a) drift due to the electric field applied to this depletion layer. In this case, holes are injected into the multiplication region, and the atoms in 1nP of InP are ionized in an avalanche manner by a high electric field, and the holes are avalanche multiplied. In
With P, the ionization rate of holes is higher than that of electrons, and the generation of multiplication carriers is almost completed in the time it takes for the injected holes to pass through the multiplication region, so there is little excess noise, multiplication of minute signals, and high-speed response can be obtained. Therefore, a combination of conduction types as shown in FIG. 26ζ is used.

[Problem to be solved by the invention]

The conventional long wavelength APD is C? - structure, a high reverse bias is applied through the front and rear if+z pairs of ohmic electrodes, and an optical signal is output. Therefore, there is a mutual influence, and an i11 frequency filter is required at the output of the APD. Also, Cd diffusion (P+
) region is affected by the depletion layer capacitance, which causes deterioration of high frequency response. The present invention was made to solve the above problems, and aims to provide an APD that does not require a high frequency filter circuit and has good high frequency characteristics.

[Means to solve the problem]

InGaAs/InGaAs according to this invention
The APD structure of P is an inversion layer type NMO5 transistor and A
In this device, PDs are combined, and electrons generated by light in a light absorption layer and multiplied in a multiplication layer are used as carriers in an n-type channel.

[Effect]

Inversion layer type NMOS transistor and A
The combined structure of PDs forms a gate region 4r-APD structure of an NMO3) transistor. Photo-excited electrons are multiplied using a depletion layer created by the gate voltage and collected under the gate wL. These electrons drift through the n-type channel and are obtained as the output of the N0M5 transistor. Therefore, the APD 4 is an AP that applies a reverse voltage and separates the bias circuit that creates a depletion layer and the output circuit that takes out the optical signal current.
D structure can be manufactured.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a cross-sectional view showing the structure of a 1 nGaAs/1 nGaAsP APD that combines an inversion layer type NMO5) transistor and an APD. In the figure, (7) and (6) are the second
This is equivalent to the conventional example shown in the figure.

Next, the manufacturing method will be explained. P+-1nP substrate (
lb) on top, P-InP buffer no 2b),
P -InGaAsP -1nGaAsP light absorption HJ
(3b), P--1nGaAsP (4b), P-1nG
The formation of the epitaxial layer of aAaP multiplication m (5b) is the same as that shown in the conventional example of FIG. However, since electrons with high mobility are used as channel carriers, the conductivity type of each semiconductor is P type, unlike the conventional example. Further, in order to multiply electrons, the ionization rate of electrons is higher than that of holes in the P-fnGaAsP multiplication layer As.

The manufacturing method according to the present invention forms a N0M5 transistor based on P-1nGaAsP. Here, (c) is an n'''' 1nGaAsP region, 04 is a drain electrode, and 4 is a source electrode. 4 is a gate electrode that transmits light, and a transparent IIE electrode such as 1nxUy or 5nxOy is used.

4 is a surface ohmic electrode that makes ohmic contact with the gate electrode □□□. αG is an n-type channel with gate voltage 6ζ.

Next, the operating principle will be explained. The light incident from the gate electrode □□□ to which the gate voltage is applied is p -I nGaAs/P-
Electrons are generated by being absorbed by the 1nGaAsP light absorption layer (3b), and the gate voltage is applied to the depletion layer (field) I, P
-The 'electrons multiplied by the InGaAsP multiplication layer (5b) become carriers of the n-type channel αQ, and the drain electrode α4
, is output from the vIL pole of the source 'dl pole μs.

〔Effect of the invention〕

As described above, according to this invention, APD! Since the reverse bias circuit for @II operation and the photocurrent output circuit are completely separated, there is no mutual influence between them, and high frequency? No filter circuit required.

In addition, there is no effect of depletion layer capacitance on the output circuit, and NMO5
Like a transistor, a simple transistor is represented by an equivalent circuit with only a low resistance, so it has the advantage of good high frequency characteristics.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of a long wavelength APD according to an embodiment of the present invention, and FIG. 2 is a sectional view showing the structure of a conventional long wavelength APD. In the figure, (1b) is a P''-InP substrate, (2b) is a P-1nP buffer layer, and (3b) is a P''-InP substrate.
'-InGaAs/P--InGaAsP light absorption layer, (4b) is P-InGaAsP, (5b
) is a P-InGaAsP multiplication layer, (7) is a protective insulating film,
OQ is the front ohmic wt pole, (11) is the back ohmic electrode, 4 is the gate electrode, and so is n+-InGaAsP.
area, α4 is the drain electrode, (4) is the source electrode, Ql
is an n-type channel. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A long-wavelength avalanche photodiode that combines an inversion layer type NMOS transistor and an avalanche photodiode, and uses electrons generated in a light absorption layer by light and multiplied in a multiplication layer as carriers of an n-type channel. .