JPS62104178A - Pin photo diode - Google Patents

Abstract

PURPOSE:To enable fast response by sequentially growing one conductivity type contact layer and one conductivity type optical absorption layer 3 on a substrate, and selectively removing both layers so that no n<+> region exists under the bonding pad, thereby reducing the capacitance. CONSTITUTION:On a Si-GaAs substrate 1, an n<+>-GaAs layer 2 as a contact layer and an n<->-GaAs layer 3 as an optical absorption layer are sequentially grown, selective etching is performed leaving the photo detecting portion of the layer 3, and selective etching is performed leaving the photo detecting portion of the layer 2 and the n-side bonding pad portion. Then, an n<->-Al0.3 Ga0.7As layer 4 as a high-resistance layer (window layer) is grown, and using as a mask a Si3N4 layer 6 formed on the surface of the layer 4 by etching, Zn is diffused to form a p<+> type region 5. A p-side ohmic electrode 8 containing the bonding pad therein and composed of Ti/Pt/Au is formed surrounding a photo detecting portion 7, and an n-side ohmic electrode 9 of AuGe/Au if formed on the layer 2. Since overlapping of the layer 2 and the electrode 8 is eliminated is both, unnecessary capacitance except for the photo detecting portion is reduced, enabling the capacitance of the whole pin diode to be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] In order to obtain a high-speed pin photodiode, a structure is proposed in which the capacitance of the pin photodiode is reduced by reducing the capacitance in areas other than the light receiving area, that is, in the bonding node area.

[Industrial application field]

The present invention relates to a pin photodiode structure with improved capacity reduction.

With the aim of increasing the speed and capacity of optical communications, research into increasing the speed of light-receiving elements is being actively conducted.

In particular, what limits the response speed of a pin photodiode is its (electrostatic) capacitance and the travel time of carriers in the depletion layer, and reducing the capacitance is particularly important for increasing speed.

[Conventional technology]

FIGS. 3(1) and 3(2) are a perspective view and a sectional view of a conventional pin photodiode.

Here, the figure number 31 is omitted for convenience of comparison with FIG. 1.

In Figure 3 (1), n1 type gallium arsenide (n ”-
An n-type gallium arsenide (n'-GaAs) layer 33 is formed as a light absorption layer on a substrate 32, and an n-type aluminum gallium arsenide (n'-GaAs) layer 33 is formed as a window layer on a substrate 32.
-Alo, 3Gao, ? AS) layers 34 are grown sequentially.

Next, n-Alo, 5Gao, ? Using a silicon nitride (SiJ*) layer 36 formed on the surface of the AS layer 34 as a mask, zinc (Zn) is diffused to form a p° type region 35.

Note that the Si, IN4 layer 36 is left as it is as a buffing basin film.

Next, the bonding pad 38^ in the p type region 35
A p-side ohmic electrode 38 made of titanium/platinum/gold (Ti/Pt/Au) is formed around the light receiving part 37.

n''-gold germanium/on the back side of GaAs-based Fi32
N-side ohmic electrode 39 made of gold (AuGe/Au)
form.

In FIG. 3(2), the p" type region 35 is formed to the full thickness of the high resistance n-^16.5 Gao, tAs layer 34 which is a window layer.

In this structure, since Zn is diffused in the bonding pad region in addition to the light receiving portion, there is a drawback that the bonding area becomes large and the capacitance becomes large.

In addition, there is a method to improve this and form the bonding pad in a region where Zn is not diffused, that is, to form it on the bancivation film, but even with this method, there is an n'' region under the bonding pad. 32, and there is no significant reduction in capacity.

[Problem that the invention seeks to solve]

In a pin photodiode with a conventional structure, the bonding pad area occupies a relatively large area! No reduction had been made.

[Means for solving problems]

The above problem can be solved by sequentially growing a contact layer (2) of one conductivity type and a light absorption layer (3) of one conductivity type on the substrate i (1). ) is selectively removed, a high resistance I'! whose resistance value is higher than that of the contact layer (2) is formed. (41), converting the high resistance layer (4) on the light absorption layer (3) into a region (5) of another conductivity type, and forming a contact layer (2) of one conductivity type and a region (5) of another conductivity type. A pin photodiode with an electrode formed thereon, and a four-conductivity type contact layer (2) grown on the substrate (1),
After selectively removing the contact layer (2), a light absorption layer (3) and a high resistance layer N (4) having a higher resistance value than the contact layer (2) are grown and selected including the light receiving region. This is achieved by converting the high resistance layer (4) into a region (5) of a different conductivity type and forming an electrode on a contact layer (2) of one conductivity type and a region (5) of a different conductivity type using a pin photodiode. Ru.

[Effect]

The present invention aims at reducing capacitance by growing an n' layer on a substrate so that there is no n'' region under the bonding pad and selectively removing this layer.

〔Example〕

FIG. 1 is a sectional view of a pin photodiode according to the first invention.

In the figure, (11) is deposited as a contact layer on a semi-insulating gallium arsenide (SI-GaAs) substrate 1 by, for example, metal organic chemical vapor deposition (MOCVD) with a carrier concentration of I x 10'''c.
n'-GaAs layer 2 with a thickness of 2 μm and a carrier concentration of 5×10 14 cm−” as a light absorption layer and a thickness of 4 μm.
m of n-GaAs layers 3 are sequentially grown.

(2) Perform selective etching leaving the light-receiving portion of the n''-GaAs layer 3 intact.

The etchant is ill□SO*+8H20□+tut.

It is.

(Selective etching is performed leaving the light receiving part of 31n'-GaAs Jii 2 and the n-side bonding pad part.

The etchant is the same as (2).

(4) By MOCVD method, 3 μm thick n-Alo, Gao,
Grow Js N 4.

(5) n-Alo, 3Gao, 43 layers in the light receiving area 4
is etched to a thickness of 0.5 μm.

(6) Zn is diffused using the 1500-thick 5ilN4 layer 6 formed on the surface of the n-8lo, zGao, q8S layer 4 as a mask to form the p° type region 5.

Note that the SiJ layer 6 is left as it is as a passivation film.

(7) Ti/Pt/Au with a thickness of 1000/1000/2000 including the bonding pad in the PE type region 5
An n-side ohmic electrode 8 made of
An n-side ohmic electrode 9 made of AuGe/Au - is formed.

FIG. 2 is a sectional view of a pin photodiode according to a second invention.

In the figure, a 5l-GaAs substrate 1 is prepared by the Tll MOCVD method.
On top, a contact layer with a carrier concentration of I x 10"
An n'-GaAs layer 2 with a thickness of 2 μm and a thickness of 2 μm is grown.

(Selective etching is performed leaving the light receiving part and the n-side bonding pad part of the 21n''-GaAs layer 2.

(3) Carrier concentration 5X1014cm- as a light absorption layer
', n-GaAs layers 3 and 1 with a thickness of 4 μm and an n-^ with a thickness of 0.5 μm as a high resistance layer (wind layer)
lo, 3Ga6. Js layer 4 is grown sequentially.

(4) n--^L, :+Gao, Using the Si3N4 layer 6 formed on the surface of the Js layer 4 as a mask, Zn is diffused to form a p' type region 5.

Note that the 5i3Na layer 6 is left as it is as a passivation film (.

(5) Selectively etching the n--GaAs layer 3 to
The n''-GaAs layer 2 in the side bonding pad forming portion is exposed.

(including a bonding pad in the 61p' type region 5, T
An n-side ohmic electrode 8 made of i/Pt/Au is formed around the light receiving part 7, and the n''-GaAs layer 2 is made of AuGe/
An n-side ohmic electrode 9 made of Au is formed.

In the structure according to the present invention, both the n·-GaAs layer 2 and the n
Since the side ohmic electrodes 8 do not overlap, unnecessary capacitance other than the light receiving portion is reduced, and the capacitance of the entire pin diode can be reduced.

〔Effect of the invention〕

As described in detail above, the pin diode according to the present invention has a reduced capacitance and is capable of high-speed response.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a pin photodiode according to the first invention, FIG. 2 is a cross-sectional view of a pin photodiode according to the second invention, and FIGS. 3 (1) and (2) are perspective views of a conventional pin photodiode. FIG. In the figure, 1 is a 5r-GaAs substrate, 2 is an n''-GaAs layer, 3 is a light absorption layer, n-GaAs Ns, 4 is a high resistance N (wind layer), and n-^l (1,3Ga@, ?AS). 5 is the p-type region 6 is the 5iJa layer 6. 7 is the light receiving part, 8 is the p-side ohmic electrode, 9 is the n-side ohmic electrode.゛ an λ ゝ t.

Claims (2)

[Claims] (1) a contact layer (2) of one conductivity type on the substrate (1);
A light absorption layer (3) of one conductivity type is grown sequentially, and a light absorption layer (3) of one conductivity type is grown.
After selectively removing 3) and the contact layer (2), a high resistance layer (4) having a higher resistance value than the contact layer (2) is grown, and the high resistance layer (4) on the light absorption layer (3) is grown. A pin photodiode characterized in that (4) is converted into a region (5) of another conductivity type, and electrodes are formed on a contact layer (2) of one conductivity type and a region (5) of another conductivity type. (2) After growing a contact layer (2) of one conductivity type on the substrate (1) and selectively removing the contact layer (2), the light absorption layer (3) and the contact layer (2) are grown. A high resistance layer (4) with a high resistance value is grown, the high resistance layer (4) is selectively converted into a region (5) of another conductivity type including the light receiving region, and a contact layer (2) of one conductivity type is grown. A pin photodiode characterized in that an electrode is formed on a region (5) of a different conductivity type.