JPH0254974A - Photodetector - Google Patents

Abstract

PURPOSE:To contrive a superhigh-speed photodetector by causing a barrier layer to be made of a resonant-tunneling barrier and causing energy levels in a well layer to be unified after narrowing the width of the well layer in the above barrier layer by turns. CONSTITUTION:A photodetector is composed of, for example, an N<+> type InP substrate 1, an n-type GaInAs buffer layer 2, an n-type AlInAs/GaInAs superlattice layer 3, an n-type GaInAs photoabsorption layer 4, an n-type InP guard ring 5, and a p<+> type diffusion region 6. A barrier layer is made of a resonant-tunneling barrier layer 41 and it is constructed so that energy levels 43a-43d in respective well layers 42a-42d are unified by narrowing properly the width of respective well layers 42a-42d in consecutive order.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to provide a light-receiving element that can reliably realize ultra-high speed with respect to a light-receiving element. In the light receiving element, the barrier layer is constituted by a resonant tunnel type barrier layer, and the width of each well layer in the resonant tunnel type barrier layer is sequentially narrowed to make the energy level in each well layer the same energy. Configure it as follows.

[Industrial application field]

The present invention relates to a light-receiving element, and more particularly, to a light-receiving element that can realize ultra-high speed.

Photodetectors that can achieve ultra-high speed and low noise include, for example, avalanche photodiodes that utilize a superlattice constructed by appropriately combining layers with a large bandgap and layers with a small bandgap. Ava
A light receiving element such as a ranche photo diode (APD, hereinafter referred to as APD) has been proposed.

An APD is typically a photodiode that applies a reverse bias near breakdown to a PN junction diode (St) to avalanche multiply the carriers generated by light.

[Conventional technology]

A conventional light-receiving element, for example, an APD using a superlattice, will be specifically described below with reference to the drawings.

FIG. 3 is a diagram illustrating a conventional light receiving element.

In this figure, 21 is an electron, 22 is a hole,
23 is a barrier layer, 24 is a well layer, and 25 is a heterointerface, which is also a superlattice interface.

This conventional light-receiving element attempts to obtain both ultra-high speed and low-noise characteristics by increasing the ionization rate of electrons 21 by, for example, utilizing the large band offset ΔEc (point A shown in Figure 3) of the conductor. That is what it is. It is already known that at point A, the ionization rate ratio of electrons and holes becomes large, making it possible to obtain both ultrahigh speed and low noise characteristics.

Next, regarding the technology of configuring the barrier layer constituting the superlattice with a resonant tunnel type barrier layer, see C, J.

Summers et al, Appl, Phys.
Lett, 48(12) 1986°P2O3. Note that although there is a report on a technology in which the barrier layer constituting the superlattice is composed of a resonant tunnel barrier layer, there is no report on a technology that uses this for an APD (avalanche, photodiode). .

Hereinafter, a detailed explanation will be given using the drawings.

FIG. 4 is a diagram illustrating a conventional resonant tunnel type barrier layer.

In this figure, 31 is a resonant tunnel type barrier layer;
2a, 32b, 32c, and 32d are well layers within the resonant tunnel type barrier layer 31. 33a, 33b, 3
3c and 33d are energy levels.

Note that the energy level 33a is the energy level of the well 132a, the energy level 33b is the energy level of the well j132b, and the energy level 33c is the energy level of the well layer 32.
The energy level c and the energy level 33d are the energy levels of the well layer 32d and are discrete.

The width of each well layer 32a, 32b, 32c, and 32d is 100 Å or less, and as shown in FIG. 4, well layer 32a>well layer 32b>well layer 32C>well layer 3
2d.

In this report, as shown in FIG. 4, each well layer 32a, 32b in a resonant tunnel type barrier layer 31.

By appropriately narrowing the widths of the well layers 3ga, 32b, 32c, and 32d, the energy levels in each well layer 3ga, 32b, 32c, and 32d are made to have the same energy, so that the electrons 21 (carriers) arriving at the edge of the point It has been reported that it is possible to pass between the levels 33a, 33b, 33c, and 33a as if in a tunnel.

[Problem to be solved by the invention]

However, in the conventional light-receiving element shown in FIG. 3, due to the large band offset ΔEc at point B shown in FIG. There was a problem in that the ultra-high speed that was supposed to be achieved was hindered. Specifically, when the electrons 21 enter the barrier layer 23 from the well 1i24, the electrons 21 stay at the barrier of the band offset ΔEc as if pile amplifying, resulting in deterioration of frequency characteristics (for example,
3001 (z (becoming leprosy)) and the frequency characteristics (GH2 order) required for the ultra-high speed required are not obtained (
It becomes.

Therefore, an object of the present invention is to provide a light-receiving element that can reliably realize ultra-high speed.

[Means to solve the problem]

In order to achieve the above object, the light receiving element according to the present invention has a superlattice structure composed of a barrier layer and a well layer, in which the barrier layer is composed of a resonant tunnel type barrier layer, and the barrier layer is composed of a resonant tunnel type barrier layer. By sequentially narrowing the width of each well layer in the barrier layer, the energy levels in each well layer are configured to have the same energy.

[Effect]

In the present invention, the barrier layer constituting the superlattice is composed of a resonant tunnel type barrier layer, and the width of each well layer in the resonant tunnel type barrier layer is sequentially narrowed, so that the energy level in each well layer is Constructed to have the same energy.

Therefore, it becomes possible for carriers (for example, electrons) to pass between the same energy levels in each well layer as if they were tunneling.
It becomes possible to prevent carriers from stagnation at the barrier of the large band offset portion, and it becomes possible to realize ultrahigh speed.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

1 and 2 are diagrams for explaining the light receiving element according to the present invention, FIG. 1 is a sectional view showing the structure of one embodiment, and FIG. 2 is a diagram for explaining the operating principle of one embodiment. be.

In these figures, 1 is made of, for example, InP, and is, for example, an n-type substrate, 2 is, for example, made of Ga1nAS, which is, for example, an n-type buffer layer, and 3 is, for example, Aj! InAs/
For example, an n-type superlattice layer made of Ga InAs, 4
is made of, for example, GaInAs, and is, for example, an n-type light absorption layer; 5 is made of, for example, InP, and is, for example, an n-type guard ring layer; 6 is, for example, a p-type diffusion region; 41 is, for example, Af
A resonant tunnel type barrier layer made of InAs and Ga1nAs (corresponding to the resonant tunnel type barrier layer according to the present invention) has a breadth and gamble energy of, for example, 1.4.
It is 5eV. 42a, 42b, 42c, 42d are Ga
The well layer is made of 1 nAs and has a band gap energy of, for example, 0.75 eV. 43a, 43b, 43
c and 43d are energy levels.

Note that here, the superlattice layer 3 is composed of an Af I nAs layer and a Ga
It is constructed by alternately combining lnAs layers of 25N each. The energy level 43a is the energy level of the well 1i42a, and the energy level 43b is the energy level of the well layer 42b.
The energy level 43C is the energy level of the well layer 42c, and the energy level 43d is the energy level of the well layer 42d, which are discrete. The width of each well layer 42a, 42b, 42C142d is 100 Å or less, and as shown in FIG. 2, the well layer 42a>well layer 42b>well layer 42C>well layer 42d. Also, the band offset ΔEc shown in FIG.

Point A and point B are the band offset Δ shown in the conventional figure 3.
Ec corresponds to point A and point B.

Next, the manufacturing method will be briefly explained.

First, a buffer layer 2 having a thickness of 2 μm, for example, a superlattice layer 3 having a thickness of 1.0 μm, for example, are formed on a substrate 1 having a thickness of 150 μm, for example, by MBE method (MO method may also be used). After sequentially forming the light absorption layer 4 of 5 μm,
For example, by wet etching, unnecessary portions at both ends of the device from the light absorption layer 4 to the buffer layer 2 are selectively mesa-etched.

Then, after forming the guard ring layer 5 so as to cover the light absorption layer 4 to the buffer layer 2 by, for example, the MBE method (the MO method may also be used), by forming the diffusion region 6 by, for example, the Zn ion implantation method, A light receiving element having a structure as shown in FIG. 1 is completed.

That is, in the above embodiment, as shown in FIG. 2, the barrier layer (corresponding to the conventional barrier layer 23 shown in FIG. 3) is composed of a resonant tunnel type barrier layer 41, and the resonant tunnel type barrier I Each well layer 42a, 42b in 'i41,
The energy levels 43a, 43b, 43c, and 43d in each well layer 42a, 42b, 42c, and 42d were configured to have the same energy by appropriately narrowing the widths of the well layers 42c and 42d, so that the electron 21 (carrier) These energy levels 43a, 43b, 43c, 43
It is possible to cause the electrons 21 to pass through the space between a as if they were tunneling, and it is possible to prevent the electrons 21 from stagnation at the wall of the large band offset ΔEc portion, and it is possible to reliably achieve ultra-high speed.

Specifically, as shown in FIG.
can pass through the resonant tunnel type barrier layer 41 by tunneling, it is possible to prevent carrier retention (retention when carriers enter the barrier from the well) due to the band offset ΔEc at point B, and This makes it possible to achieve high-speed characteristics. In addition, since the threshold energy of the electron 21 can be lowered by the band offset ΔEc at point A, the ionization rate of electrons (the ionization rate when carriers enter the well from the barrier) can be dramatically increased. It is possible to achieve low noise characteristics.

Note that in the above embodiment, the resonant tunnel type barrier layer 41
Although the case has been described in which the well layer is made of Al11 nAs and the well layer is made of GaInAs, the present invention is not limited to this.
s, the well layer may be made of GaAs Sb.

〔effect〕

According to the present invention, there is an effect that ultra-high speed can be reliably realized.

[Brief explanation of the drawing]

1 and 2 are diagrams explaining the light receiving element according to the present invention, FIG. 1 is a cross-sectional view showing the structure of one embodiment, FIG. 2 is a diagram explaining the operating principle of one embodiment, FIG. 3 is a diagram illustrating a conventional light receiving element, and FIG. 4 is a diagram illustrating a conventional resonant tunnel type barrier layer. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Buffer layer, 3...Superlattice layer, 4...Light absorption layer, 5...Guard ring layer, 6...diffusion region, 41...resonant tunnel type barrier layer, 42a,
42b, 42c, 42d-=well layer, 43
a, 43b, 43c, 43d・----・Energy level. ＼ Nn $ 4/)-a Ward 61

Claims (1)

[Claims] In a light-receiving element having a superlattice structure composed of a barrier layer and a well layer, the barrier layer is composed of a resonant tunnel type barrier layer, and each well in the resonant tunnel type barrier layer A light-receiving element characterized in that the energy levels in each of the well layers are configured to have the same energy by successively narrowing the width of the layers.