JPS63182959A - Photoelectric conversion device - Google Patents

Abstract

PURPOSE:To improve reproducibility with halftone by means of a CdS system photoconductive device having a large photoelectric current and to realize fast reading, by using a photoconductive device which shows the characteristic of the rise time of the photoelectric current of two and half or more times the fall time. CONSTITUTION:The photoconductive device which shows the characteristic of the rise time of the photoelectric current of two and half or more times the fall time is used. And a device is formed so that, out of the beams of light of a light source, a stationary bias beam of light due to a minimum reflected light component from an original, an inductive light system, and a leakage component from the neighborhood of the system is projected on the photoconductive device, and the rise time of the photoelectric current goes under twice the fall time. As the photoconductor film, a material in which a II-IV compound semiconductor is used as an organism is used. For example, as the photoconductor film, the material in which a CdS, a CdSe, or a CdS-CdSe is used as the organism is used. And by using a sensor array having a device to satisfy a condition of Cu concentration=0.05-0.3mol%, and film thickness=3250-5000Angstrom and using a photoelectric conversion device in which a LED array and an optical focusing fiber array are combined, the reading speed more than 4ms/line assuming the illuminance of an original plane as 100lux, can be obtained. Also, superior reproducibility with halftone can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a photoelectric conversion device for inputting images of various kinds of digital devices such as facsimiles and intelligent copiers.

Background of the Invention In recent years, advances have been made in miniaturizing the image input units of various office automation equipment such as facsimiles and improving image distortion, and the development and practical use of photoelectric conversion devices, so-called contact-type line sensors, whose dimensions are the same as the width of the document. It has progressed.

It is very advantageous to use a photoconductive element that can obtain a large photocurrent as the light receiving section of such a line sensor because the peripheral circuitry is simple. Among photoconductive elements,
The one using CdS-CtlSe has an order of magnitude larger photocurrent and has been put into practical use the most.

On the other hand, with the demand for improved quality and faster information transmission, there is a strong desire to improve the proportionality of the photocurrent flowing through the photoconductive element to the illuminance and the optical response speed.

The improvement in both characteristics improves the reproducibility of halftones and enables high-speed reading.

Problems to be Solved by the Invention The proportionality of the photocurrent J flowing through a photoconductive element to the illuminance is usually expressed as J p oc L+γ. For Cd5-CdSe cells with large photocurrent (for example, composition ratio 6:4), the normal document surface illuminance is 5o~100
The γ value of dux is as small as 0.6 to 76.

In order to faithfully reproduce the halftones of a read image, the closer the γ value is to 1, the better, but it is desirable that the γ value is at least 0.8 or more.

However, the photoresponse speed of a photoconductive element is determined by the rise time τr (the time it takes for Jp to rise from 0 to the saturation value of 50 degrees) and the fall time τ (1 (the time it takes for Jp to rise from the saturation value to 60 degrees) of the photocurrent).
It can be expressed as the time it takes for the value to drop to 0%). Cd5-CdS
e sensor (composition ratio 6:4), τ1 is 3 to s ms for pulsed light of 100 dux.

τd is slow at 2.5~3ms, and the actual reading speed is 1°~
Limited to SMS/dine.

The present invention aims to provide a photoelectric conversion device that has significantly improved the above-mentioned drawbacks.

Means for Solving the Problems The present invention forms a plurality of photoconductive elements arranged in the main scanning direction on an insulating transparent substrate, each of which has a photoconductor film provided with a counter electrode. In a photoelectric conversion device in which the light reflected from the original hits a photoconductive element through a light guide system, such as a focusing optical fiber array, the rise time of the photocurrent is 2.5 times or more the fall time. Using a photoconductive element that exhibits A photoelectric conversion characterized in that the light due to the leakage component always hits the photoconductive element as bias light (3 to 6% or more), and the rise time of the photocurrent is less than twice the fall time. It is a device.

Effect: For example, in the case of a Cd5-CdSe sensor, increasing the amount of Ca or decreasing the film thickness decreases the photocurrent Jp and its fall time τd, while increasing the rise time τ1 and the γ value. By designing τ, = τdX (2,5 to 10), τr≦τd×2 can be achieved by irradiating a large number of steady bias lights, and a significant increase in speed is possible. Even if the composition ratio of CdSe is increased, τr=τd×5 can be achieved, but the bias light effect is much smaller.

Embodiment The above invention utilizes the following embodiment, that is, the fact that in a photoconductive element using a photoconductor film that can obtain a large photocurrent, if the fall time of the photocurrent is designed to be small, the γ value can be increased. This is achieved by Specifically, for example, when using a Cd5-1dse photoconductor film, it is necessary to add a large amount of Cu, or to add Cd5-CdS.
This is achieved by reducing the film thickness of e. τr is τ
When d is 2.5 to 10 times, a significant decrease in τ1 is observed by adding only about 3 to 5% of steady bias light, and it is possible to reduce τ1 to less than twice τd. Even if the composition ratio of Cd5-CdSe is changed, τr can be made much larger than τd. For example, if the composition ratio is set to 228, τ1 will be about 6 times τd, but in this case, it will be about 3 to 5 times. It is not possible to make r approximately twice as large as τd in terms of the bias light component.

The photoconductor film is preferably composed entirely of H-VI group compound semiconductors, especially cas, casθ, or Cd5-Cd5θ, and it is particularly effective to include small amounts of O and/or C1 as impurities. Addition of Cu increases the γ value, and addition of Cg increases the photocurrent. A photoconductor film made entirely of CdS, CdSe or Cd5-CdSe is heated to a high temperature of 470 to 600'C.
When heated in an atmosphere containing 1C12 vapor, a particularly large photocurrent can be obtained and excellent stability can be obtained. This CdS, CdS
The amount of Cu in a film using e or Cd5-CdSe is preferably 0.06 molar or more and 0.3 molar or less, and in a film heated in an atmosphere containing CdCd2 vapor, the film thickness is 3260 Å or more and 500 Å or more. The following will give particularly good results. When the Cu amount is less than 0.05 molti and the film thickness is more than 6000 Å, the improvement of the γ value is insufficient and τd is also large, and when the Cu amount is more than 0.3% and the film thickness is less than 325°, Jp becomes small. It ends up.

Other, more specific examples will be described. In other words, the glass substrate (Koji/Gryo069.230
7) Above, Cd5o6Sθ. , 4: A Cu thin film is formed by vapor deposition, and 1728 bits are arranged in an island shape in the main scanning direction at a rate of 8 bits/ff by photoetching. After heating this island-like film at 550'C in an atmosphere containing each2 vapor to form a photoconductor film, each island-like film was coated with NiCr/
Form U's opposing electrodes, that is, a common side electrode and individual side electrodes. The gap between the opposing electrodes was 60 μm, and the width of the island-shaped film was 100 μm. Note that the amount of Cu in the photoconductor film is o, 0 with respect to the matrix Ca5o, 6Sso, 41 mo/L=
1 to 0.5 mol%, and the film thickness is 3000 to 55oO
It's a person.

Of each photoconductive element array produced in this way, each
We selected each element and measured its characteristics. That is, DC1
LE flashes at 1 field (o, 5 seconds each) under 0V application
D light (s7o, w) was irradiated, and the photocurrent, its rise time, fall time, and γ value (between 50 and 100 lux) were determined with the illuminance on the photoconductive element surface set to 100 dux. In addition, the characteristics when irradiated with 31 ux steady bias light using the same type of LED were also measured. The effect of this on Jp and γ is small, so it is ignored.

These results are summarized in Table 1 (a) and (b).

(a) is a film with a constant film thickness (4,500 people) and the Cu concentration is changed, and (b) is a film with a constant Cu concentration (0.1 mol%) and a change in film thickness. The top row is J.

(μm) [τr (ms) - τd (ms)) γ, and the bottom row shows [τr (mS) - τd (m
s)].

(IL) Film thickness: 4SoO (b) Cufi degree: 0.1 mol% It was found that a high γ value and high-speed response can be obtained by increasing the Cu concentration and decreasing the film thickness.
, rp, > 10μ, τr, τd≦2.4mB (4
corresponding to a reading speed of ms/1ine), γ〉o, s
The conditions to satisfy 1 are (a), Cu concentration = 0.05 to 0.3
Mok %, (b) film thickness = 3260-500o.

Using a sensor array having elements that satisfy the above conditions, L
Using a photoelectric conversion device combined with an ED array and a light-focusing 7-eyebar array, a reading speed of 4m515ins or more can be obtained when the illuminance of the document surface is 1001ux.
Moreover, the reproducibility of intermediate tones is extremely excellent.

Effects of the Invention According to the present invention, a photoelectric conversion device using a CdS-based photoconductive element with a large photocurrent, excellent in reproducibility of halftones, and capable of high-speed reading can be obtained, which has great industrial significance.

Claims (6)

[Claims] (1) On an insulating transparent substrate, a plurality of photoconductive elements each having a photoconductor film provided with a counter electrode are formed side by side in the main scanning direction,
In a photoelectric conversion device configured such that illumination light from a light source hits a document and reflected light from the document passes through a light guide system and hits a photoconductive element, the rise time of the photocurrent is 2.5 times longer than the fall time.
Using a photoconductive element that exhibits a characteristic more than double that of the light source, steady bias light from the minimum reflected light component (black background) from the document and leakage components from the light guide system and its surroundings is transmitted to the photoconductive element. A photoelectric conversion device characterized in that the rise time of the photocurrent is twice or less than the fall time. (2) The photoelectric conversion device according to claim 1, wherein the photoconductor film is made of a II-VI group compound semiconductor as a living body. (3) The photoconductor film is CdS, CdSe or CdS-
The photoelectric conversion device according to claim 2, characterized in that it is made of CdSe as a living body. (4) Claim 3, characterized in that the photoconductor film contains a small amount of Cu and/or Cl as an impurity.
The photoelectric conversion device described in . (5) The amount of Cu in the photoconductor film is 0.05 mol% or more, 0
．． 5. The photoelectric conversion device according to claim 4, wherein the content is 3 mol% or less. (6) The thickness of the photoconductor film is 3250 Å or more and 5000 Å
A photoelectric conversion device according to claim 5, characterized in that: