JPS63285977A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To extremely reduce noise and to remarkably accelerate a semiconductor photodetector by using a superlattice for an APD magnifying layer, employing a substance having larger band gap than that of a well layer for a window and guard ring layer to rigidly provide a guard ring effect. CONSTITUTION:An n-type superlattice (n-type Al0.48In0.52As/Ga0.47In0.53As) 2 as a magnifying layer, an n-type Ga0.47In0.53As layer 3 as an optical absorption layer, and an n-type InP layer 4 having larger band gap than that of the GaInAs of a barrier layer as a window and guard ring layer are sequentially grown on an n<+> type InP substrate 1. Then, Zn or Cd is diffused as a P-type impurity from the surface of the layer 4 to form a p<+> type region 5. The layer structure of the n-type superlattice is formed by alternately laminating 20-30 layers of N-type A InAs layers having 150Angstrom of thickness and an impurity concentration <=1X10<15>cm<-3>, and 20-30 layers of N-type GaInAs layers having 150Angstrom of thickness and impurity concentration <=1X10<15>cm<-3>. Thus, an APD having rigid guard ring effect using the superlattice amplifying layer is obtained, and low noise and superhigh speed due to the use of the superlattice are provided.

Description

[Detailed description of the invention] [Summary] APD (Avalanche Photodiode)
), a superlattice APD is proposed in which the guard ring effect is strengthened by using a superlattice for the multiplication layer and using a material with a larger band gap than the well layer for the wind layer and guard ring layer.

Enables ultra-low noise and ultra-high speed.

[Industrial application field]

The present invention is an ultra-high speed, ultra-low noise AP using a superlattice in the multiplication layer.
Regarding the structure of D.

With the development of long-distance, high-capacity optical communication systems.

There is a demand for ultra-high-speed, low-noise APDs with flat electric field distribution.

[Conventional technology]

In recent years, attempts have been made to use superlattices in APDO multiplication layers.

The reason is as follows.

That is, if the APDO multiplication layer contains a superlattice 1 such as A11n
When an As/GaInAs superlattice is used and electrons are injected into it, the barrier height at the interface between the AlInAs barrier layer and the GaInAs well layer of the superlattice is extremely larger in the conduction band than in the valence band, so the electron ionization rate α increases. The ionization rate ratio α/β of electrons and regular bills becomes much larger than that of holes, i.e., the ionization rate ratio α/β of electrons and regular bills becomes large, resulting in Muffkintyre (Mc I n
(tyre) effect reduces the noise of the APD, and also reduces the build-up time of the multiplied electrons, making it possible to make the APD extremely high-speed.

Conventionally, no specific structure for APD using a superlattice has been proposed.

Therefore, as a conventional example, the structure of an InP-based 1 μm band APD will be described below.

FIG. 3 is a cross-sectional view of a 1 μm band InP-based APD to explain a conventional example.

Next, the structure will be explained in order of steps.

In the figure, on an n''-InP substrate 31.

A 33° n-GaInP layer was grown as a light absorbing layer and a 33° n-InP layer as a multiplication layer, and mesa etching was performed leaving the periphery of the light receiving area.
An nJnP layer 34 is embedded around the mesa.

Zn or Cd is diffused as a p-type impurity from the surface of the light-receiving region of the n-InP layer 34, 33 to form a p'''' type region 35.

Next, the p-side electrode 36゜n''-I on the p+ type region 35
An n-side electrode 37 is formed on the back surface of the nP substrate 31 to complete the formation of the main part of the APD.

[Problem that the invention seeks to solve]

In conventional APDs, the multiplication region and the guard ring region are made of semiconductors with the same bandgap, and the difference in breakdown voltage between the light receiving region and the guard ring region is small.

[Means for solving problems]

The solution to the above problem is to use a multiplication layer made of a superlattice in which barrier layers with a large band gap and well layers with a small band gap are alternately laminated on a substrate.

A window layer/guard ring layer made of a semiconductor of one conductivity type having a larger band gap than the well layer of the superlattice is provided on the multiplication layer, and the window layer/guard ring layer in a region including the light receiving region is provided. This is achieved by a semiconductor light receiving device made of a different conductivity type.

[Effect]

The present invention utilizes the low breakdown voltage of the light-receiving region of the superlattice APD and the high breakdown voltage of the guard ring layer with a large band gap to obtain a strong guard ring effect.

〔Example〕

FIG. 1 shows an example of the present invention using an AlInAs/GaInAs superlattice multiplication layer.
It is a sectional view of PD.

Next, the structure will be explained in order of steps.

In the figure, on the +n''-InP substrate 1.

An n-type superlattice (n-Alo, 4alno
, sJs/Gao, 4tIno, 53AS) 2
+n-Gao as light absorption layer, 4tin0.53A
S layer 3゜N-InPn as a wind layer and guard ring layer, which has a larger band gap than GaInAs of the barrier layer.
Grows sequentially.

Zn or Cd is diffused as a p-type impurity from the surface of the n-InPn series layer to form a p-type region 5.

The dimensions of each layer are as follows.

Drawing number Substance name r-hunt Concentration Thickness cIl
l-3) (μm) 5p”-6i area Zn lXl0I91.04
n-InP Sn lXl0” 1.5
3 n-GaInAs Anne F-bu 5X
10" 2.02 n-superlattice undoped - -1n"-1nP
Sn lXl0" 350.
What is the layer structure of the 0n-superlattice?

Thickness: 150, impurity concentration ≦lXl0"cn+-'n
-20 to 30 AlInAs layers.

Thickness: 150, impurity concentration ≦1×10'sC "3-n-
20 to 30 GaInAs layers are alternately stacked.

Next, an n-side electrode 7 is formed on the p-side electrode 6° on the p-type region 5 and on the back surface of the n''-InP substrate 1, completing the formation of the main part of the APD.

FIG. 2 is a diagram showing the distribution of the electric field E with respect to the distance X in the depth direction of the APD of the present invention.

The distance X in the depth direction is measured in the substrate direction with the pn junction plane as O, and the electric field E (V cm-') gradually decreases in the light absorption layer 3, but becomes constant in the superlattice multiplication layer 2.

It shows a rapid decrease within the substrate 1.

In the conventional InP-based APD, α/β=2.5. Although the excess noise figure was F=5,
In the case of the superlattice APD of the example, α/β=10. The excess noise figure improved to F=2-3.

Furthermore, the bandgap is InP of the guard ring is 1.35 eV.

8tlnAs of the barrier layer is 1.45 eV.

GaInAs in the well layer has a voltage of 0.75 eV.

(or light absorption layer), the breakdown voltage of the example is 80% with an InP guard ring.
~100 V, and 30 to 40 V in the multiplication layer of the superlattice, providing a sufficient breakdown voltage difference and a strong guard ring effect.

In the example, InP was used for the guard ring.

AlInAs, which is the same as the barrier layer, may be used instead, but since it is a ternary crystal, growth is more complicated than with InP.

Furthermore, in the example, AlInAs/Ga1n is added to the superlattice.
AlSb/GaSb was used instead of As.

Similar effects were obtained using AlGaSb/GaSb and InP/GaInAs.

〔Effect of the invention〕

As explained above, according to the present invention, an APD having a strong guard ring effect using a superlattice multiplication layer can be obtained,
In addition, low noise and ultra-high speed can be achieved by using a superlattice.

[Brief explanation of drawings]

Figure 1 shows an example of the present invention using an AlInAs/Ga1nAs superlattice multiplication layer.
A cross-sectional view of PD. FIG. 2 is a diagram showing the distribution of electric field E with respect to distance X in the depth direction of the APD of the present invention. FIG. 3 is a cross-sectional view of a 1 μm band InP-based APD to explain a conventional example. In fig. 1 is an n''-InP substrate. 2 is a multiplication layer made of n-superlattice (n-AlInAs/Ga1n
As). 3 is a light absorption layer, which is an n-GalnAs layer. 4 is an n-InP layer which is a wind layer and a guard ring layer. 5 is a p-type region 6 is a p-side electrode. 7 is the n-side electrode not fired ■■ f) Danshu 2 Rod 1st revision report East A row of southern action shouts 3 concave

Claims (1)

[Claims] A multiplication layer made of a superlattice in which a barrier layer with a large bandgap and a well layer with a small bandgap are alternately laminated on a substrate, and a conductive layer having a larger bandgap than the well layer of the superlattice on the multiplication layer. 1. A semiconductor light-receiving device comprising: a window layer/guard ring layer made of a type semiconductor, and a region including a light-receiving region of the window layer/guard ring layer is made of a different conductivity type.