JPH0567805A - Avalanche photodiode - Google Patents

Abstract

PURPOSE:To eliminate a tunnel current in a sheet dope layer between an optical absorption layer and a superlattice multiplication layer and prevent a deterioration of high-frequency characteristic by a pileup of a carrier. CONSTITUTION:In a sheet dope layer put between an In0.53Ga0.47As layer 5 of an optional absorption and an In0.52Al0.48As/In0.8Ga0.2As0.6P0.4 superlattice multiplication layer 3, an In0.8Ga0.2As0.6P0.4 layer 12 is formed on a side near to the In0.53Ga0.47As layer 5, and an In0.52Al0.48As layer 11 is formed on a side near the In0.52Al0.48As/In0.8Ga0.2As0.6P0.4 superlattice multiplication layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an avalanche photodiode applied to a photodetector for optical communication.

[0002]

2. Description of the Related Art Avalanche photodiodes (hereinafter referred to as APDs) for optical communication having a wavelength of 1.3 μm or 1.55 μm
Ge) -APD or InP / In.
GaAs heterojunction APDs have been used. In these APDs, Ge or InP is used as a carrier multiplication layer.
Is used.

Generally, the multiplication noise of APD is an ionization rate (α) of electrons and holes, which is a quantity peculiar to a semiconductor used in a multiplication layer.
And the ratio of β) become smaller as the ratio deviates from 1. But,
Since Ge and InP have a ratio close to 1, there is a problem that noise is large. In order to solve this, it has been conventionally proposed to use a superlattice structure in the multiplication layer to increase one of α and β and increase the ratio of α / β or β / α.

In particular, In _0.52 A lattice-matched with the InP substrate
l _0.48 As / In _0.53 Ga _0.47 As layer and In _0.52 A
It has been confirmed that the l _0.48 As / In _x Ga _1-x As _y P _1-y layer has a large α due to a large discontinuity in the conduction band, and is effective in reducing noise.

In order to make use of such characteristics of the superlattice to produce a low noise and high speed APD, only electrons out of electrons and holes generated by light absorption are selectively formed in the superlattice multiplication layer. Avalanche multiplication must be done by injection. For this purpose, the light absorbing layer must be separated from the superlattice multiplication layer and the light absorbing layer must be p-type. It also controls the avalanche breakdown in the light absorption layer,
In order to limit the place where avalanche amplification occurs only to the superlattice region, it is necessary to make a difference in electric field strength between the superlattice multiplication layer and the light absorption layer.

As a structure for satisfying all such requirements, a thin InGaA having a high p-type impurity density between the light absorption layer of p ^-- InGaAs and the superlattice multiplication layer.
A patent has already been filed for a structure sandwiching an s layer (called a sheet dope layer) (Japanese Patent Application No. 1-1119146). In addition, since InGaAs having a small band gap is used for this sheet-doped layer, when a tunnel current is generated in this layer, In _0.52 Al _0.48 A having a larger band gap is used.
The tunnel current can be controlled by using the s layer, the InP layer, or the In _x Ga _1-x As _y P _1-y layer (Japanese Patent Application No. 3-760620).

FIG. 3 shows the structure of the device according to this patent application. In the figure, 1 is an n ⁺ -InP substrate, 2 is an n ⁺ -InP buffer layer, 3 is a non-doped I
n _0.52 Al _0.48 As / In _0.8 Ga _0.2 As _0.6 P _0.4 superlattice multiplication layer, 4 has an impurity density of 8 × 10 ¹⁷ cm ⁻³ and a thickness of 16
0 Å p-type InP layer (sheet dope layer), 5 has an impurity density of 2 × 10 ¹⁵ cm ⁻³ and a thickness of 2 μm p-type In _0.53 Ga
_0.47 As layer, 6 has an impurity density of 2 × 10 ¹⁷ cm ^-3 and a thickness of 5
P-type In _0.53 Ga _0.47 As layer of Å, 7 is an impurity density of 1 × 10 ₁₈ m ^-3, a p-type InP layer with a thickness of 1000 Å, 8 is an impurity density of 1 × 10 ¹⁸ m ^-3, a thickness of 1000 Å p-type In
_0.53 Ga _0.47 As layer, 9 is AuGeNi electrode, 10 is A
uZnNi electrode.

In such a structure, the electric field is weakened in the InP layer 4 as the sheet dope layer, and only a small electric field is applied to the light absorption layer using the In _0.53 Ga _0.47 As layer 4 having a small band gap. In addition, the generation of tunnel current here is suppressed. A high electric field is applied to part of the InP layer 4 (on the multiplication layer side), but no tunnel current is generated because the bandgap of this layer is large.

[0009]

FIG. 4 shows the band structure of this avalanche photodiode.
In the figure, In _0.52 Al _0.48 As / In _0.8 Ga _0.2
Since the As _0.6 P _0.4 superlattice multiplication layer 3 has almost no valence band discontinuity, holes with large effective mass are not piled up, and In _0.52 Al _0.48 As / In _0.8 G
a _0.2 As _0.6 P _0.4 It can pass through the superlattice multiplication layer 3, but when the InP layer 4 is used as the sheet dope layer, the InP layer 4 as the sheet dope layer and the In _0.52 Al _0.48 A
Since there is a discontinuity in the valence band between the superlattice multiplication layer 3 and the s / In _0.8 Ga _0.2 As _0.6 P _0.4 superlattice multiplication layer 3, there is a problem that holes are piled up here. On the other hand, when a semiconductor having a small valence band discontinuity with the superlattice multiplication layer such as InAlAs is used for the sheet dope layer, conduction between the In _0.53 Ga _0.47 As layer 5 as a light absorption layer is used. The discontinuity of the belt becomes large. Although electrons have a smaller effective mass than holes, electrons are piled up at the interface between the light absorption layer and the sheet dope layer due to the weak electric field. Such pile-up of carriers has a problem that the high frequency characteristics of the avalanche photodiode are significantly deteriorated.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to eliminate a tunnel current in a sheet-doped layer between a superlattice multiplication layer and a light absorption layer. Another object of the present invention is to provide an avalanche photodiode that prevents deterioration of high frequency characteristics due to pile-up of carriers.

[0011]

In order to achieve such an object, the present invention provides a sheet dope layer sandwiched between a light absorption layer and a superlattice multiplication layer, and a layer close to the light absorption layer. InGa
AsP is arranged and InAlAs is formed in a layer close to the superlattice multiplication layer.
Is arranged.

[0012]

In the present invention, the discontinuity of the conduction band between the sheet-doped layer and the light absorption layer and the discontinuity of the valence band between the sheet-doped layer and the superlattice multiplication layer are reduced.

[0013]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing a configuration and an electric field intensity distribution of each layer according to an embodiment of the avalanche photodiode according to the present invention. In the figure, 1 is an n ⁺ -InP substrate, 2 is an n ⁺ -InP buffer layer, 3 is a non-doped I
_{n 0.52 Al 0.48 As / In 0.} 8 Ga 0.2 As 0.6 P 0.4 superlattice multiplication layer, 11 is an impurity density of 8 × 10 ¹⁷ cm ^-3, thickness 8
0 Å p-type In _0.52 Al _0.48 As layer, 12 is p-type In _0.8 Ga _0.2 A with an impurity density of 8 × 10 ¹⁷ cm ^-3 and a thickness of 80 Å
s _0.6 P _0.4 layer, 5 is a p-type In _0.53 Ga _0.47 As layer having an impurity density of 2 × 10 ¹⁵ cm ⁻³ and a thickness of 2 μm, and 6 is a p-type In having an impurity density of 2 × 10 ¹⁷ cm ⁻³ and a thickness of 500 Å. _0.53 Ga
_0.47 As layer, 7 has an impurity density of 1 × 10 ₁₈ m ⁻³ and a thickness of 10
00Å p-type InP layer, 8 has an impurity density of 1 × 10
¹⁸ m ^-3 , p-type In _0.53 Ga _0.47 As with 1000 Å thickness
Layers, 9 are AuGeNi electrodes, and 10 are AuZnNi electrodes. Of these, In _0.52 Al _0.48 As / In _0.8 Ga
_0.2 As _0.6 P _{0 .4} thickness of the superlattice multiplication layer 3, 0.52Myu
The thickness of the In _0.8 Ga _0.2 As _0.6 P _0.4 well layer is 200Å, and the thickness of the In _0.52 Al _0.48 As barrier layer is 20 m.
0Å, the superlattice period is 13.

FIG. 1 shows the distribution of the electric field strength of each layer.
In_0.52Al_0.48As / In_0.8Ga_0.2As_0.6P
_0.4 The largest electric field is applied to the superlattice multiplication layer 3,
Nschier multiplication occurs here. In_0.53Ga_0.47As layer 5
Is a light absorption layer, and this In_{0. 53}Ga_0.47As light absorption layer
And In_0.52Al_0.48As / In_0.8Ga_0.2As_0.6P_0.4
The difference in electric field strength from the superlattice multiplication layer 3 is that the impurity density is large.
In_0.52Al_0.48As layer 11 and In_0.8Ga_0.2A
s_0.6P_0.4Made by layer 12. Also, the InP layer 7
Is a window layer for preventing surface recombination.

In _0.52 Al _0.48 As / In _0.8 Ga _0.2 A
InGaAsP is used for the well layer of the s _0.6 P _0.4 superlattice multiplication layer 3 because a large electric field is applied to the superlattice multiplication layer, so that the bandgap in this portion is increased to increase the darkness due to the tunnel effect. This is to suppress the current.
The In _0.53 Ga _0.47 As light absorption layer 5 has to have a small band gap in order to absorb the signal light having a wavelength of 1.55 μm, and therefore In _0.53 Ga _0.47 As is used. Therefore, in order to suppress the tunnel effect in this portion, the electric field strength must be 1.5 × 10 ⁵ V / cm or less. In _0.52 Al _0.48 As layer 11 and I
Reducing the electric field strength in the sheet-doped layer of the n _0.8 Ga _0.2 As _0.6 P _0.4 layer 12 prevents avalanche breakdown in the light absorption layer and also suppresses the tunnel effect.

On the other hand, in the sheet-doped layer, the electric field strength changes abruptly. In particular, In _0.52 Al _0.48 As / In _0.8
Ga _0.2 As _0.6 P _0.4 In _0.52 A close to the superlattice multiplication layer 3
In the _0.48 As layer 11, the electric field strength is large and a tunnel current is generated. In order to prevent this, in the present invention, the sheet-doped layer is made of InAl having a large band gap.
As was used. On the other hand, In _0.8 Ga _0.2 As _0.6 P _0.4 layer 1
In 2, it may be already using smaller semiconductor band gap than the In _0.52 Al _0.48 As layer 11 to the electric field is weakened by In _0.52 Al _0.48 As layer 11.

FIG. 2 shows the band structure of the avalanche photodiode of this embodiment. The incident signal light is In
It is absorbed in the _0.53 Ga _0.47 As layer 5 to generate electron-hole pairs. Of these, electrons are In _0.52 Al _0.48 As / In _0.8 Ga _0.2 As due to the electric field in the In _0.53 Ga _0.47 As layer 5.
_0.6 P _0.4 Swept in the direction of the superlattice multiplication layer 3. Electron is I
n _0.52 Al _0.48 As / In _0.8 Ga _0.2 As _0.6 P _{0.4 To} be injected into the superlattice multiplication layer 3, In _0.52 Al _{0.48 As}
The conduction band discontinuity of the sheet-doped layer composed of the s layer 11 and the In _0.8 Ga _0.2 As _0.6 P _0.4 layer 12 must be overcome, but as is clear from FIG. As a result, the individual discontinuities are extremely small, and electrons can successively cross the conduction band discontinuities.

On the other hand, by ionization, In _0.52 Al _0.48
The holes generated in the As / In _0.8 Ga _0.2 As _0.6 P _0.4 superlattice multiplication layer 3 _travel toward the In _0.53 Ga _0.47 As layer 5. Sheet dope layer and In _0.52 Al _0.48 As / In
_Since there is no valence band discontinuity with the _0.8 Ga _0.2 As _0.6 P _0.4 superlattice multiplication layer 3, holes can pass through the sheet-doped layer without being piled up.

In the above-described embodiment, the In _0.52 Al _0.48 As layer 11 and the In _0.8 Ga are used as the sheet dope layer.
_{The case where the 0.2} As _0.6 P _0.4 layer 12 and the In _0.8 Ga _0.2 As _0.6 P _0.4 layer 12 are used has been described.
Big _{In x Ga 1-x As y} P 1-y (0 <x <1,0 <y <1) the same effects as described above even by using a layer of a band gap than an In _0.53 Ga _0.47 As layer is obtained Needless to say.

[0020]

As described above, in the avalanche photodiode according to the present invention, since there is no pile up of carriers in the sheet-doped layer, the tunnel conduction current in the sheet-doped layer is not deteriorated without deteriorating the high frequency characteristics. An extremely excellent effect that generation can be suppressed can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an avalanche photodiode according to an embodiment of the present invention and a diagram showing electric field intensity distribution of each layer.

FIG. 2 is a diagram showing a band structure of the avalanche photodiode shown in FIG.

FIG. 3 is a cross-sectional view showing a configuration of a conventional avalanche photodiode and a view showing electric field intensity distribution of each layer.

FIG. 4 is a diagram showing a band structure of a conventional avalanche photodiode.

[Explanation of symbols]

1 n ⁺ -InP substrate 2 n ⁺ -InP buffer layer 3 Undoped In _0.52 Al _0.48 As / In _0.8 Ga
_0.2 As _0.6 P _0.4 Superlattice multiplication layer 5 p-type In _0.53 Ga _0.47 As layer 6 p-type In _0.53 Ga _0.47 As layer 7 p-type InP layer 8 p-type In _0.53 Ga _0.47 As layer 9 AuGeNi electrode 10 AuZnNi electrode 11 p In _0.52 Al _0.48 As layer 12 p In _0.8 Ga _0.2 As _0.6 P _0.4 layer

Claims (1)

[Claims] 1. In _0.52 Al lattice-matched to an InP substrate
_0.48 As as a barrier layer In _0.53 Ga _0.47 As or I
A superlattice having n _x Ga _1-x As _y P _1-y as a well layer is a carrier multiplication layer, and p is separated from the superlattice carrier multiplication layer.
In _0.53 Ga _0.47 As as a light absorption layer, InGaAsP is arranged between the superlattice carrier multiplication layer and the light absorption layer in a layer close to the light absorption layer, and the superlattice carrier multiplication layer is formed. An avalanche photodiode characterized by arranging InAlAs in a layer close to the.