JPH02206180A - Manufacture of photoconductive thin film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing a photoconductive thin film mainly composed of CdS, CdSe, or a solid solution thereof (hereinafter referred to as CdS/CdSe).

BACKGROUND OF THE INVENTION It is already known to produce photoconductors by heating thin films mainly composed of CdS, CdSe, or CdS/CdSe at high temperatures in a suitable atmosphere. Methods for forming this thin film include chemical precipitation and vacuum evaporation. Also, Cd51 Cd581 or CdS /
In order to impart photoconductivity to Cdse, it is common to add a small amount of a halogen, particularly CQ, etc., and a metal, particularly Cu1Au, etc., and heat it to a temperature of 5°C or higher.

The photoconductive thin film obtained by this method is 0.4 to 0.8 μm if it is mainly composed of CdS, and if it contains CdSe, it is sensitive to light with an even longer wavelength, and at the same time the response time is shortened. It has been known.

The introduction of Cg into the film significantly increases the photocurrent (hereinafter referred to as J), but at the same time it also considerably increases the dark current (hereinafter referred to as Jd). On the other hand, when introducing Cu, it is possible to reduce J, so generally, when introducing C1, Cu is co-added to increase J and reduce Jd. Specifically, when CutJI degree is high, Jpl Jd is small, and when it is low, Jpl Jd is small, and when CutJI degree is low, Jpl Jd is small.
Jd increases.

Regarding the response time, the time required for the photocurrent to reach 50% from O is the rise time τ1, and the time from the saturation value to 50% is the rise time τ1.
If the fall time until it decreases to % is τd, then Cu
When the concentration is high, τ is large and τd is small; when the concentration is low, τ is small and τd is large. Also Cu
By adding , it becomes sensitive to light with a wavelength longer than the band gap due to electrons excited from the impurity level created by Cu.

Therefore, the Cu concentration is appropriately adjusted to obtain the required photoelectric characteristics. As described above, the Cu concentration in a thin film has a great influence on the photoelectric properties of the thin film, and accurate control of the Cu concentration is very important in producing practical devices.

Next, a conventional method for manufacturing a photoconductive thin film will be described.

First, in the chemical precipitation method, in a solution (SC (MHI 2, CdCff2, NH4OH, N
Cu is mixed into H4C51) etc. as CuCR2, and the Cu concentration is controlled by the concentration.

The first method in the vapor deposition method is Cd51Cd S e
, or CdS/CdSe as the main
An evaporation source is prepared by mixing uCffa. Then, while evaporating the deposition main component, Cu is also evaporated at the same time to form, for example, a CdS/Cd5a:Cu film. In this case, Cu18 degrees is CuC mixed in when producing the evaporation source.
It was controlled by the concentration of N2. Another method is to keep the concentration of CuCl12 mixed during the preparation of the evaporation source constant,
In this method, the main components are evaporated at 900 to 1000°C in the first step, and then, in the second step, the evaporation source is raised to a higher temperature to evaporate Cu to form CdS/CdSe:Cu. The concentration of Cu was controlled by the temperature of the second stage crucible.

Furthermore, the thin film produced as described above was heat-treated at 500 to 000C for about 1 hour in an atmosphere containing 060g2.

Problems to be Solved by the Invention Chemical precipitation methods have problems such as complicated steps and poor reproducibility of characteristics, and are not used much at present.

On the other hand, thin films formed by vapor deposition are low-resistance films with many defects such as Sl 8e, and although this condition can often be improved by heat treatment in an atmosphere containing S or Se,
incomplete. Also, the main components evaporate at 800~1ooo''C, while Cu evaporates at 1100~1500℃.
Requires. Therefore, when the main component and Cu are evaporated at the same time, some Cu is incorporated into the film, but after the evaporation is finished, it remains in the crucible in the form of CuS, etc., increasing the Cu concentration in the film. Moreover, it is difficult to obtain reproducibility and control of characteristics is difficult. In addition, if Cu is mixed by increasing the temperature of the evaporation source after evaporating the main component, Cu
Since Cu is deposited later, a large amount of Cu exists on the surface, and a concentration gradient occurs, which means that the concentration is not uniform even after heat treatment.
This causes problems with the characteristics. As described above, the conventional method has problems in the method of manufacturing the film and the method of controlling the Cu concentration.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a method for manufacturing a photoconductive thin film that overcomes the above-mentioned problems.

Means for Solving the Problems The present invention mainly consists of Cd51 Cd581 or CdS/CdSe on an insulating substrate, and a trace amount of CuCR is added to this.
The method is characterized in that a thin film is produced by a sputtering method using a target containing CdCl 2 and then heat-treated in an atmosphere containing CdCl 2 to produce a photoconductive film.

Further, preferably CuCR2 contained in the target is 0
．． The range is 0.005 to 0.1 mo1%.

Function: In the method for producing a photoconductive thin film according to the present invention, Ca
51 By adding CuCR2 to a target mainly composed of CdSe1 or CdS/CdSe and forming a thin film by sputtering, it is possible to easily create a thin film with high J, precise control of Cu concentration, and even distribution of i. and also have excellent photoelectric properties after heat treatment. In other words, CLI can be controlled accurately and easily using the sputtering method.

The concentration of CuCl2 is 0.0 with respect to the main component of the target.
The reason why it is set to be 0.05 mo1% or more and 0.1 mo1% or less is because if it is 0.005 mo1% or less, Jd and τ become too large and sufficient sensitivity to red light cannot be obtained. 0.1 mo1% or less is 0.1 m
This is because when o1% or more, J becomes too small and τ becomes too large.

Example Examples of the present invention will be described in detail below.

In order to make a sputtering target, CdS
0.6 mol of Cd5a and 0.4 mol of Cd5a are mixed, and a plurality of types of CuCl2 are weighed out in the range of 0.001-0.2 mol, and each is added to the above-mentioned mixture of CdS and CdSe. Each of these mixtures was calcined in an inert gas at 800°C for 1 hour, cooled, and then ground. Place this as a powder in a stainless steel dish, solidify it, and use it as a target.
, T-rewo shatta device (ANELVA 5PF312
) and #7059 (Corning) as the substrate.
, (40X 40X 1.1mm"), approx.
It was deposited to a thickness of 5000 μm. The deposition conditions were a substrate temperature of 200°C, a discharge power of 0, and 57 w/crl.
The sputtering gas is Ar and its pressure is IliOmtorr.
It is.

The film thus formed was placed in an alumina box lined with a powder of CdS and CdCl2 on the bottom.
Heat treatment was performed at 0°C for one hour. A counter electrode of NlCr was formed on these thin films by electron beam evaporation. The ratio of the gap width to the gap length of the counter electrode is 0.5.

The figure shows S of a sample formed by the method of the present invention (before heat treatment).
The relationship between the measurement results of Cu concentration (signal intensity CC of Cu with respect to Cd) by IMS (secondary ion mass spectrometry) and the concentration of CuC2 mixed in when creating the evaporation source is shown. From this result, it can be seen that the Cu concentration in the film is almost proportional to the concentration of CuCR2 mixed in when producing the evaporation source, indicating good controllability.

(Leaving space below) T: Heat treatment temperature (°C) Jp: Photocurrent (pA) Jd: Dark current (pA) τr: Rise time (ms) τd: Fall time (ms) The table shows the conventional vapor deposition method and the method of the present invention. An example of the measurement results of the photoelectric properties of thin films produced by sputtering at different heat treatment temperatures will be shown for comparison. J is smaller and the photoresponse time is also shorter than in the case of fabrication using conventional methods.

In this example, Cd5ta, a/CdSe! ! , s, but it is clear that similar effects can be obtained with CdS, CdSe1, and other compositions of CdS/CdSe.

Effects of the Invention As described above, according to the method for producing a photoconductive thin film of the present invention, compared to conventional methods, it is possible to control the Cufi degree more accurately and to make its distribution uniform, and as a result, The properties of the device can be controlled well and the reproducibility is excellent, and its industrial value is great.

[Brief explanation of the drawing]

The figure shows Cd of Cu in SIMS of a photoconductive thin film produced by the method for producing a photoconductive thin film in one embodiment of the present invention.
The signal intensity ratio to
It is a figure which shows the relationship of pH degree.

Claims (2)

[Claims] (1) On an insulating substrate, CdS or CdSe or a solid solution thereof is used as the main component, and a trace amount of CuCl_
1. A method for producing a photoconductive thin film, comprising forming a thin film by a sputtering method using a target containing CdCl_2 and heat-treating the film in an atmosphere containing CdCl_2. (2) The method for producing a photoconductive thin film according to claim 1, wherein the concentration of the CuCl_2 contained in the target is in the range of 0.005 to 0.1 mol%.