JPH0128893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an infrared detector, and particularly to an infrared detector having infrared detection capabilities in different wavelength bands.

Infrared devices that detect and recognize a target object by detecting infrared rays emitted from the target object use infrared sensing elements with different response wavelength bands to improve the ability to identify the target object. It is preferable to use an infrared detector with pairs placed close together within the detector. This is similar to the fact that color TVs have the ability to distinguish between different colors, which increases the amount of information that can be detected compared to black and white TVs. Development is actively underway.

FIG. 1 shows an example of the ideal spectral sensitivity of an infrared sensing element having two desirable response wavelength bands for such an infrared detector.
The spectral sensitivity curve A of the sensing element for detecting long wavelength infrared rays does not overlap with the spectral sensitivity curve B of the sensing element for detecting short wavelength infrared rays, and the two spectral sensitivity curves A and B are almost completely separated. .

However, ordinary infrared sensing elements generally detect short wavelengths (i.e., wavelengths with large photon energy).
Since it responds to any wavelength of infrared rays, the two spectral sensitivity curves a and b overlap as shown in Figure 2. If so, the discrimination ability of the above-mentioned infrared detector will be significantly reduced.

In order to prevent such overlap of spectral sensitivity curves, for example, two different types of bandpass filters may be used, or two types of bandpass filters may be created using interference on the light-receiving surface of each infrared sensing element. Methods such as forming a multilayer film may be considered, but the former method makes it difficult to install each bandpass filter very close to the infrared sensing element, which is arranged close to each other, and the latter method is difficult because the infrared sensing element material is generally susceptible to heat. Because of its weakness, it has the disadvantage that it is nearly impossible to form multilayer films that require high temperatures for deposition.

Furthermore, in the case of the above-mentioned infrared detector, the discrimination ability should increase as the number of paired infrared detecting elements increases, but in the case of such a multi-element infrared detector, it is also possible to use the above-mentioned bandpass filter. Furthermore, it becomes even more difficult to form two types of multilayer films that have a filter effect.

The present invention has been made in view of these drawbacks, and includes providing a first multi-component semiconductor layer having a relatively large forbidden band width on a substrate that transmits infrared rays, and a predetermined portion of the first multi-component semiconductor layer on the first multi-component semiconductor layer. 1st
A plurality of second multi-component semiconductor layers having the same conductivity type as the multi-component semiconductor and having a small forbidden band width are arranged in a regular island pattern, and the first multi-component semiconductor layer is provided on the partially exposed surface of the first multi-component semiconductor layer. and a second photodiode is arranged on the surface of each of the second island-like multi-component semiconductor layers, and each of the first and second photodiodes has a different wavelength for infrared rays incident on the substrate side. It is an object of the present invention to provide an infrared detector characterized by having a band light detection ability, which will be described in detail with reference to the drawings from FIG. 3 onwards.

FIG. 3 is an embodiment showing a cross-sectional view of the main structure of an infrared sensing element, which is a main part of an infrared detector according to the present invention, in which the forbidden band width Eg is, for example, 1.6ev.
Cadmium telluride (CdTe) large enough as
A first multi-component semiconductor layer 2 having a relatively large forbidden band width Eg of, for example, 0.4ev is formed on one main surface of the substrate 1 by an epitaxial growth method or the like. and the first multi-component semiconductor layer 2
In the upper predetermined portion 11, a second multi-component semiconductor layer 3 having a forbidden band width Eg of, for example, about 0.2 ev is formed by epitaxial growth or the like. This is a portion where the surface of the first multi-component semiconductor layer 2 is exposed by removing the semiconductor layer 3 by, for example, etching.

The first and second multi-component semiconductor layers 2 and 3
are both p-type, for example, but a first n-type impurity having a conductivity type opposite to that of the multi-component semiconductor layers 2 and 3 is present in the exposed predetermined portion 12 of the first multi-component semiconductor layer 2. A doped layer 7 is provided to form a first photodiode, and a second n-type impurity doped layer 8 is provided in a predetermined portion 11 of the second multi-component semiconductor layer 3 to form a second photodiode. is forming. Note that 4 is a surface protective film made of, for example, zinc sulfide (Z _o S), and
and an extraction electrode 9 in contact with the impurity doped layers 7, 8 forming the second photodiode.
10 (for example, made of indium or the like) is disposed on the Z _o S surface protection film 4 . In addition, what is shown as 5 covering the other main surface of the CdTe substrate 1 on which the light (infrared rays) hν ₁ and hν ₂ are incident as shown by the broken lines C and D is applicable.
An anti-reflection film for incident light on the CdTe substrate surface,
This is made of Z _o S, for example.

The infrared sensing element shown in FIG. 3 can therefore be said to form a two-layer heterojunction structure of multi-component semiconductors, and the first and second impurity-doped layers 7 and 8 form a so-called back-illuminated photodiode. It can be said that it has become.

Further, 6 is a bandpass filter whose transmission wavelength is 1 to 6 μm, and the infrared rays hν ₁ and hν ₂ are transmitted through this bandpass filter 6 and are incident, but the forbidden band width of the CdTe substrate 1 is 1.6 μm. ev, infrared rays with wavelengths longer than 0.8 μm are absorbed by the CdTe substrate 1. Therefore, the CdTe substrate alone has the effect of blocking infrared rays with wavelengths longer than 0.8 μm, and has the same effect as being opaque to infrared rays of this wavelength. Therefore, if this characteristic is utilized, the filter shown as 6 does not need to be one that only passes light in the 1-6 μm band, and may be a high-pass filter that blocks wavelengths of 6 μm or more.

By the way, as above, the passband is 0.8~
Of the two types of light that are limited to 6 μm and enter as indicated by the wavy lines C and D, the first light that enters along the wavy line C has a forbidden band width Eg of 0.4ev.
is incident on the multi-component semiconductor layer (Hg _0.6 Cd _0.4 Te layer), but in this layer, among the wavelengths of the above incident light, 0.8 to 3μ
Infrared radiation with a wavelength of m is absorbed. Therefore, in the first photodiode 7 formed in the first multi-component semiconductor layer 2, this light with a wavelength in the range of 0.8 to 3 μm is photoelectrically converted, and the output is outputted via the extraction electrode 9. Ru.

On the other hand, before the light incident along the wavy line D reaches the second photodiode 8, the light passes through the first multi-dimensional semiconductor layer (Eg=0.4ev).
As described above, since the light must pass through the first semiconductor layer 2, the light is absorbed in the range of 0.8 to 3 μm in the first semiconductor layer 2. Therefore, for example, Hg _0.73 Cd _0.27 Te passes through the first multi-component semiconductor layer 2.
The light entering the second multi-component semiconductor layer 3 (Eg = 0.2ev) consisting of 0.8 to 3 μm wavelength components is lost, and only the 3 to 6 μm wavelength components remain. There is. Therefore, in the second photodiode 8 formed in the second multi-component semiconductor layer 3, this light with a wavelength in the range of 3 to 6 μm is photoelectrically converted, and the output is outputted via the extraction electrode 10. Ru.

That is, by fabricating the first and second photodiodes forming a pair of infrared sensing elements in the first and second multi-semiconductor layers 2 and 3, respectively, A and B in FIG. Discretely separated spectral sensitivity characteristics as shown can be obtained.

Incidentally, the number of photodiodes is not limited to two, that is, one pair, as shown in Figure 3. For example, the number of photodiodes is not limited to two, that is, a pair, but for example, the composition of each layer can be changed sequentially by forming a first, second, and third multi-component semiconductor layer, thereby increasing the forbidden band width. For example, 3
If the spectral sensitivity characteristics shown in FIG. 1 are changed to stages, the spectral sensitivity characteristics shown in FIG. Furthermore, in the above embodiment, a multilayer HgCdTe layer was epitaxially grown on a CdTe substrate, but as a multi-component semiconductor material,
Not limited to HgCdTe, for example, a plurality of first and second lead-tin tellurium (P _b S _o T _e ) layers having different compositions and different forbidden band widths Eg are formed on a lead-tellurium (PbTe) substrate. It is also possible to form an infrared sensing element.

In addition, as is well known, infrared sensing elements are often made into two-dimensional optical sensors by combining these multi-element devices with a charge transfer device (hereinafter referred to as CCD), but CCDs cannot be constructed from multi-component semiconductors. Therefore, it is necessary to make the CCD section on a silicon (Si) substrate, and the optical sensor section to be constructed using multiple semiconductor layers as described above, and to combine the two using a so-called face-down bonding method to create a so-called hybrid configuration. may occur.

Figure 4 is a sectional view of the main parts showing the structure of a so-called infrared CCD (also called IRCCD) in such a case, and the same parts as in Figure 3 are given the same symbols, but the parts that are different from Figure 3 are according to the rules. The main difference is that there is no extraction electrode for extracting the signals detected by the photodiodes 7 and 8 arranged in the same direction. Indium (In) was used instead of this extraction electrode.
The bumps 25 made of the same material send the detection signal charges in the direction of the arrow H and are introduced into the input diode 23 of the CCD. The sent detection signal charges are then sent in parallel, for example, in a direction perpendicular to the plane of the paper, and read out by the transfer electrodes 26 of the CCD. However, although 21 is a Si substrate of the CCD and 22 is a silicon dioxide (S _i O ₂ ) film covering the substrate, the bandpass filter 6 shown in FIG. 3 is omitted in this FIG. There is.

If the infrared detector according to the present invention described above is used, the ability to identify a target object can be greatly improved, and therefore, great practical effects can be expected.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the ideal spectral sensitivity of an infrared sensing element having two desirable response wavelength bands;
FIG. 2 is a diagram showing the spectral sensitivity characteristics actually obtained, FIG. 3 is a diagram showing an example of the main structure of the detection element of the infrared detector according to the present invention, and FIG. 4 is a modification of the present invention. It is a figure showing an example. 1: CdTe substrate, 2: first multidimensional semiconductor layer,
3: Second multi-component semiconductor layer, 4: Surface protective film, 5:
Anti-reflection film, 6: band pass filter, 7: first
photodiode, 8: second photodiode,
9, 10: Extraction electrode, 11: Predetermined portion of second multi-component semiconductor layer, 21: Silicon substrate, 22:
SiO ₂ film, 23: input diode, 25: bump.

Claims (1)

[Claims] 1. On a substrate 1 that transmits infrared rays, a first multi-component semiconductor layer 2 having a relatively large forbidden band width is provided.
At the same time, a plurality of second multi-component semiconductor layers 3 having the same conductivity type as the first multi-component semiconductor and having a small forbidden band width are formed in a regular island-like pattern at a predetermined portion on the first multi-component semiconductor layer. A first photodiode 7 is disposed on the partially exposed surface of the first multi-component semiconductor layer, and a second photodiode 8 is disposed on the surface of each of the second island-like multi-component semiconductor layers, An infrared detector characterized in that each of the first and second photodiodes has the ability to detect infrared light incident from the substrate side in different wavelength bands.