JPS6290986A - Array type infrared detector - Google Patents

Abstract

PURPOSE:To reduce leakage current of a P-N junction, to improve a resolution and to simplify the manufacturing steps by forming a mask provided with a terminal to which a voltage of a conductor of the shape for interrupting incident infrared light is to be applied to a region except the P-N junction through an insulating film on a semiconductor photodetecting surface side. CONSTITUTION:A P-type HgCdTe film 1, an N-type HgCdTe film 2, a substrate 3 of a detector, a passivation film 4, N-type side and P-type side electrodes 5, 6 and a gate 8 are formed. Since the infrared ray is incident from the opposite side to a substrate, the substrate is not necessary formed of transparent CdTe for the infrared light. When the gate 8 uses, for example, aluminum of approx. 5,000Angstrom thick, it does not pass infrared light or visible light. Accordingly, the gate for reducing the leakage current of a P-N junction is used also as a mask for preventing photon from being incident to a portion except the P-N junction. An electric connection of the detector with an exterior is obtained by the portion projected at a part of each electrode gate. Thus, since the dark current of the detector is reduced by a voltage applied to the gate, the sensitivity of the detector itself is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the structure of an array type photovoltaic infrared detector using a semiconductor.

(Prior art and its problems) Arrayed photovoltaic infrared detectors using semiconductors mainly have a structure in which pn junctions of semiconductors are arranged. In this structure, minority carriers generated by incident infrared light near the pn junction diffuse to the junction, become an electrical signal, and are output. As a semiconductor material for a detector, HgCdIe is most often used as a material capable of achieving high performance.

FIG. 3 is a cross-sectional view of a configuration example of a detector using HgCdTe. In Figure 3, 1 is p-type Hg□-8C
d, I'e (x is usually 0.2 or 0.3, the former is an infrared detector for the 10m wavelength band, and the latter is 3 to 5
(for leverage), 2 is n-type Hg made by ion implantation, etc.
CdTe layer, 3 is the substrate of the detector, 4 is a passivation film (Zns or Sin is generally used), 5 and 6
are an n-side electrode and a p-side electrode, respectively. In this figure, infrared light is incident from above, but p-type H
If gCdTe 1 is made into a crystal by epitaxial growth, the CdTe that became the growth substrate can be used as it is as the substrate 3, and since CdTe is transparent to infrared light, infrared light is input from the bottom when used. It is also possible. A drawback of the structure shown in FIG. 3 is that there is a depletion layer on the surface of the p-type HgCdTe layer under the passivation film 4.
Alternatively, an n-type reversal report may be formed. When these are formed, they become a source of generation-recombination current (GR current) between the pn junctions, increasing leakage current through the surface between the pn junctions. In an infrared detector using a pn junction, if the leakage current is large, the sensitivity as a detector decreases. In particular, in the case of infrared detectors using HgCdTe crystals, for example, Semiconductors and Semimetals No. 18
Volume (Sem1conductorSand Semim
etalsvol, 1B (1981) Acade
mic Press), Hgo
, 5cde, sTe, Hga, ycde
In both cases, the leakage current is mainly attributed to the G-R current at the operating temperature of the detector (below 77 for the former and 150 for the latter), which significantly deteriorates the detector characteristics. Cause.

In order to improve this point, for example, IEEE Elec Device Letters (IEEE Elec
tron Device Letters EDL-1
(1980) 12) and Journal of Vacuum Science and Technology (1980) 12) and Journal of Vacuum Science and Technology.
Vacuum 5science and Iechnol
ogy A3(1) (1985) 280), a structure in which a gate is provided around a pn junction has been proposed. In this structure, by applying an appropriate voltage to the gate and controlling the voltage on the p-type HgCdTe surface directly under the gate, the depletion layer or inversion layer on the surface is removed and good detector characteristics are obtained.

FIG. 4 is a sectional view of the configuration of an array type infrared detector using this structure. In this structure, a gate 8 is provided on the passivation film 4, and by controlling the gate voltage, the surface leakage current is minimized and the detector is operated. In this method, the wiring above the p-type HgCdre 1 is complicated, so a substrate 10 for wiring is provided and wiring is performed on it. Therefore, in the structure No. 45!3, infrared light cannot be used by entering it from above, but must be used by entering it from below. Therefore, as the substrate of the detector, CdTe, which is transparent to infrared light, must be used, and other materials such as sapphire may be bonded to the substrate, depending on the infrared light transmittance of the adhesive. This is not possible due to the problem of Therefore, this configuration can be achieved by epitaxially growing H on a substrate transparent to infrared light, such as CdTe.
This is only the case when gCdTe crystal is used.

Furthermore, a common drawback of the detectors having the structures shown in FIGS. 3 and 4 is that the image quality deteriorates when the distance between the unit elements in the array is reduced. When using an array type infrared detector, incident infrared light is imaged with a mirror or the like, and the detector is placed on the focal plane to obtain an output for each unit element. This prime element can be considered as each pn junction, that is, the portion where the n-type layer 2 is formed in both FIGS. 3 and 4. Infrared light does not enter only above (or below) the n-type layer 2, but also enters between adjacent n-type layers. The minority carriers generated at this time have a diffusion length (for example, p-type Hgb, 5 cda
, *In the case of I'e, if it is within several 10 to 100)QTI), it will diffuse to the junction and become the output of the element.

If the interval between unit elements is within the diffusion length, minority carriers generated in this interval can diffuse into any nearby pn junction. Therefore, output signals due to minority carriers generated during this time are distributed to adjacent unit elements, causing resolution deterioration.

In order to improve the resolution, it is necessary to reduce the element area and element spacing, but even if these are reduced, good resolution cannot be obtained.

Therefore, an object of the present invention is to provide a pn junction leakage 11! in an array type photovoltaic infrared detector. The object of the present invention is to obtain an array-type infrared detector with a small flow, good resolution, and a simple manufacturing process.

(Means for Solving the Problems) Means provided by the present invention to solve the above-mentioned problems is an array type infrared detector in which a plurality of pn junctions are arranged on a semiconductor, the pn junctions being arranged on a semiconductor. A conductive mask that blocks infrared light from entering areas other than the junction is formed on the light-receiving surface side of the semiconductor via an insulating film, and the mask has a terminal to which a voltage is to be applied. Features (Embodiments) Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2. FIGS. 1 and 2 are a plan view and a sectional view, respectively, of an example in which the present invention is applied to a one-dimensional array type infrared detector (one embodiment of the present invention). In the figure, 1 is p
type HgCdTe, 2 is n-type HgCdTe, 3 is the detector substrate (sapphire, CdTe, etc.), 4 is the passivation film (Zns, Sign, etc.), 5 and 6 are the n-side and p-side electrodes, respectively, and 8 is the gate. be. In this detector, since the infrared light is incident from the upper side, that is, the side opposite to the substrate, it is not necessary to use Cd's or the like as the substrate, which is transparent to infrared light. Therefore, this structure can be applied not only when using an epitaxially grown ugcaTe crystal but also when using a crystal obtained by a bulk growth method. If, for example, M having a film thickness of about 5,000 is used as the gate 8, infrared light or visible light will not pass through it. Therefore, infrared light does not enter the p-type HgCdTe1 directly under the gate. In other words, the feature of this detector is that p
The gate to reduce the leakage current of the n-junction is a pn
The point is that it also serves as a mask to prevent photons from entering areas other than the bonded area.

Electrical connection between the detector and the outside can be obtained by bonding or the like to a partially protruding portion of each electrode gate, as shown in the upper part of FIG. This makes it possible to connect this array type detector to, for example, a Si CCD or MOS switch array. The leakage current of the pn junction, that is, the dark current of the detector, can be reduced by WEE applied to the gate, which not only improves the sensitivity of the detector itself, but also increases the efficiency of charge injection into the CCD, for example. As a result, a high-performance one-dimensional electronic scanning infrared detector can be obtained.

Further, in this embodiment, since the gate also serves as a mask for blocking infrared rays, the complexity of the structure can be kept to a minimum. That is, the structure and manufacturing process are significantly simpler than a detector in which a gate and a light-shielding mask are provided separately to achieve similar characteristic improvements. Moreover, compared to the structure shown in FIG. 3, the only difference is that a metal film to become the gate 8 is embedded in the passivation film 4, and a terminal to which a voltage can be applied is provided in a part of the metal film. The manufacturing process is not very complicated.

(Effects of the Invention) Therefore, according to the present invention, it is possible to obtain an array-type infrared detector that has a small dark current, good resolution, and a relatively simple manufacturing process.

[Brief explanation of drawings]

FIG. 1 is a plan view of a one-dimensional array type infrared detector which is an embodiment of the present invention, and FIG. 2 is a sectional view thereof. Third
1 and 4 are cross-sectional views showing conventional array-type infrared detectors of different types. In the figure, 1 is p-type HgCdTe, 2 is n-type HgC
dTe, 3 is the substrate, 4 is the passivation film, 5 is n(
Jl electrode, 6 a p-side electrode, 7 a CdTe substrate, 8 a gate, 9 a gate electrode, and 10 a wiring substrate, respectively. Agent Patent Attorney Shinsuke Honsho Figure 1 n The gangsters Figure 2 Figure 3 Passive 4 n

Claims (1)

[Claims] In an array type infrared detector in which a plurality of pn junctions are arranged on a semiconductor, an insulating film is provided on the light-receiving surface side of the semiconductor, and a conductive mask is arranged to block infrared light from entering areas other than the pn junctions. 1. An array-type infrared detector, characterized in that the mask is formed through a mask, and a terminal to which a voltage is to be applied is provided on the mask.