JPH07147425A - Infrared detector - Google Patents

Abstract

PURPOSE:To provide a diode which has excellent characteristics by forming an n-type area which has Hg between lattice as donor on a p-type compound semiconductor crystal formed by successively laminating a first p-type compound semiconductor layer and a second p-type compound semiconductor on a substrate CONSTITUTION:Entered infrared ray is absorbed by an As doped p-HgCdTe layer 2, a p-HgCdTe layer 3 which has the Hg hole as accepter and an n<->- HgCdTe area 5 which has Hg between lattice generated by ion implantation as donor. The infrared rays are diffused as electrons or holes, are electrically separated by an pn-junction interface 8 and are outputted as a signal from an electrode 7. At that time, not much lattice defects that cause dark current is found in the vicinity of the pn-junction. Thus, element yield reduction due to incomplete heat treatment is eliminated and a HgCdTe diode which has excellent characteristics is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a semiconductor having a narrow band gap,
Particularly, the present invention relates to an infrared detector using a compound semiconductor containing Hg.

[0002]

2. Description of the Related Art It is generally known that an infrared detector using a semiconductor having a narrow band gap has high sensitivity. Among them, the photovoltaic element having a pn junction in the detection portion is very effective for an infrared imaging device having a configuration in which single elements are two-dimensionally arranged.

A photovoltaic infrared detector using HgCdTe, which is a typical example, will be briefly described with reference to FIG. H on the CdTe substrate 1 using the MBE method
The gCdTe layer is epitaxially grown and heat-treated in an Hg atmosphere to form a p-HgCdTe layer 3 composed of Hg vacancies. After that, ion implantation is partially performed using a resist mask to form the ion implantation region 4. Further, in order to avoid characteristic deterioration due to ion implantation damage, heat treatment is performed to diffuse interstitial Hg into the depth of the crystal. n
^- forming a -HgCdTe region 5, to move the pn junction interface 8 to the damage free areas. Finally, the protective film 6 and the electrode 7 are formed to complete the device.

The incident infrared ray is absorbed by the p-HgCdTe layer 3 and the n ^-- HgCdTe region 5, diffuses as an electron or a hole, is electrically separated at the pn junction portion, and is electrically separated at the electrode 7 (on the p side) as a signal. The electrodes are omitted here).

[0005]

However, such an infrared detector has the following drawbacks.

As described above, the ion implantation method is used for the formation of the pn-type junction, which is the most advantageous method in view of controllability and simplicity. In order to improve the characteristic deterioration due to ion implantation damage, the subsequent steps are performed. It is a general method to heat-treat. By this heat treatment, the interstitial Hg generated by the ion implantation diffuses through the Hg vacancies in the p-HgCdTe layer 3 to form a pn junction in a region free from ion implantation damage, but the diffusion is relatively fast. Moreover, it is difficult to sufficiently control the diffusion front, that is, the pn junction interface 8 because it also largely depends on the number of Hg vacancies. In particular, when a thin crystal having an HgCdTe layer of about 10 to 15 μm is used as the epitaxial crystal, the pn junction may move to the vicinity of the interface with the substrate having a large amount of lattice strain by heat treatment,
There is a possibility that characteristic deterioration such as increase of dark current may be caused.

An object of the present invention is to provide an infrared detector which eliminates these drawbacks.

[0008]

A photovoltaic infrared detector according to the present invention is an infrared detector using a compound semiconductor containing Hg, which is a first compound semiconductor layer in which a p-type dopant is doped on a substrate. , P with Hg vacancies as acceptors
In the p-type compound semiconductor crystal in which the second type compound semiconductor layers of the type are sequentially stacked, an n-type region using Hg between the lattices as a donor is formed.

[0009]

The infrared detection device in which a plurality of compound semiconductor layer to the action substrate, large Hg ₁ x values on CdTe substrate conventionally _{- x} Cd _x Te buffer layer and the x value smaller Hg _{1 - x} Cd _x A diode in which a Te layer is laminated has already been proposed (JP-A-1-233777, etc.). This is a device intended to selectively reduce the carrier concentration only in a portion where a diode is formed and to reduce crosstalk between each diode (pixel). In such a structure, it is impossible to control the diffusion of Hg, and the object of the present invention could not be achieved.

On the other hand, the infrared detector of the present invention has a layer doped with a p-type dopant such as As near the interface with the substrate, and a p-type layer having Hg vacancies as an acceptor thereon. Using a type HgCdTe crystal, a normal process including forming a pn junction diode by ion implantation and heat treatment after implantation is performed. P-type HgC having the above two-layer structure
Since the dTe crystal is used, the interstitial Hg diffused through the Hg vacancies by the heat treatment stops at the layer doped with the p-type dopant having almost no Hg vacancies. Therefore, the pn junction position does not reach the vicinity of the interface with the substrate where a large amount of lattice strain exists, and the deterioration of diode characteristics such as an increase in dark current due to it does not occur.

[0011]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. The manufacturing method of the present invention in which a photodiode is formed on two layers of p-type HgCdTe crystals having different types of acceptors will be briefly described.

An As-doped p-HgCdTe layer 2 having a thickness of 5 μm and a non-doped HgCd substrate 1 is formed on the CdTe substrate 1.
Te is grown to 5 μm sequentially by the MBE method, and Hg vacancies are formed in non-doped HgCdTe by p-annealing in an Hg atmosphere to form the p-HgCdTe layer 3 by the Hg vacancies. After that, boron (B) is partially ion-implanted through a mask of about 50 μmφ to form a pn junction.
Ion implantation energy may be about 150 keV. At this time, the n-type donor is activated B and Hg between the lattices generated by ion implantation. From the ion implantation damage region near the ion implantation region 4, pn
Heat treatment is performed at 150 to 200 ° C. for about 1 hour in order to separate the joints. At this time, Hg between lattices is p-HgCdTe.
Diffuses through Hg vacancies in layer 3 to form n ^-- HgCdTe
While forming the region 5, the pn junction position is entirely moved to the outside, but the diffusion in the depth direction is caused by the As-doped p-
It stops at the interface with the HgCdTe layer 2. This is the interstitial H
This is because there are almost no Hg vacancies in the p-HgCdTe layer 2 that help the diffusion of g. Since this interface is formed by a series of growth and there is no deviation of the lattice constant, it is a region where the interface level and the trap level caused by lattice defects and the like are very small. After that, the protective film 6 and the electrode 7 are formed to complete the device.

Next, the operation will be briefly described. The incident infrared rays are As-doped p-HgCdTe layer 2 and Hg.
P-HgCdTe layer 3 and n ^-- HgCdT due to holes
It is absorbed in the e region 5, diffused as electrons or holes, electrically separated at the pn junction, and output as a signal from the electrode 7 (the p-side electrode is omitted here).
At this time, as described above, in the structure of the present invention, the number of lattice defects in the vicinity of the pn junction, which causes dark current, is very small, so that a diode having good characteristics can be obtained.

As described above, according to the present invention, a pn junction can be formed with good controllability at a position away from the vicinity of the interface with a CdTe substrate having many lattice defects such as strain. Hg with good characteristics without deterioration
The CdTe diode can be manufactured with good reproducibility.

In this embodiment, the case where the p-HgCdTe layer is used as the compound semiconductor having a narrow band gap is shown. However, if the pn junction forming mechanism involving the diffusion of Hg is the same, the material, process conditions, etc. are the same. It is not limited to.

[0017]

As described in detail above, the present invention provides an HgCdTe diode having good characteristics without lowering the yield of the device due to indeterminacy of heat treatment, and contributes sufficiently to the high performance of the infrared detector. It is a thing.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an HgCdTe diode that is an embodiment of the present invention.

FIG. 2 is a sectional view for explaining a conventional HgCdTe diode.

[Explanation of symbols]

1 CdTe substrate 2 p-HgCdTe layer doped with As 3 p-HgCdTe layer with Hg vacancies 4 ion implantation region 5 n ^-- HgCdTe region 6 protective film 7 electrode 8 pn junction interface

Claims (1)

[Claims] 1. In an infrared detector using a compound semiconductor containing Hg, a first compound semiconductor layer doped with a p-type dopant on a substrate and a p-type second compound semiconductor layer having Hg vacancies as an acceptor. A photovoltaic infrared detector in which an n-type region having Hg as a donor between the lattices is formed in a p-type compound semiconductor crystal in which the above are sequentially stacked.