JPS63300559A - Array type infrared-ray detector - Google Patents

Abstract

PURPOSE:To improve the uniformity of a dark resistance by reducing the resistance from each of arrayed photodiodes to its common electrode. CONSTITUTION:In order to improve the characteristics, such as sensitivity and the like of an obtained sole photodiode, the acceptor concentration of a P-type Hg0.8Cd0.2Te layer 2 is set to approx. 10<16>cm<-3>. When the acceptor concentration of a P<+> type layer 3 is set to 10<17>cm<-3> or above, the resistivity of the layer 3 can be set to 1/10 or below of the layer 2. Accordingly, if the P-type side electrode of each photodiode is commonly provided through the layer 3, the resistance from the P-type side electrode 7 to each photodiode can be extremely reduced. Consequently, since the dark resistance of each single detector in the array approaches the resistance of a net n<+>-P junction, its dark resistance becomes uniform.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to the structure of an array type infrared detector.

(Prior Art) Generally, it is known that infrared detectors using semiconductors with a narrow bandgap have high sensitivity. In particular, a detector having a configuration in which single detection elements are arranged one-dimensionally or two-dimensionally is very effective when used in an infrared imaging device.

The configuration of a conventional array type infrared detector is, for example, as described in the magazine "NISPI (S, P, 1.E) J (Second Edition).
67, 1901, p. 18), CdT
There is one that uses an n+p junction formed in an array on Hg1-XCdxTe epitaxially grown on e as a sensing element.

FIG. 2 is a cross-sectional view showing the structure of this detector. In FIG. 0, 1 is a semi-insulating CdTe substrate, 2 is a p-type Hg1), BCdO, 2Te layer epitaxially grown thereon, and 4 is the p-type I11 layer epitaxially grown thereon. ．． ．． 8c (04 layer formed on 10,2Te by a method such as ion implantation, 5 is 5i02
6 is an electrode on the 14th layer side, 7 is an electrode on the p layer side, 8 is a signal processing unit such as a silicon CCD, and 10 is an infrared light incident on the detector. The detector shown in the figure is capable of detecting infrared light with a wavelength of about 10 μm. As a single sensing element, the lower n+p layer is
It is a photodiode that utilizes a + combination, and is arranged in an array. At this time, the n" side electrode 6 is taken from each element, but the p! electrode 7 is taken from p-type Hgo, gcdg,
2Te It is taken from one place in 2. Further, these electrodes are connected to a silicon CCD chip 8, and the output from each detection element is read out after being converted into a form that is easy to read by a signal processing section such as a CCD.

(Problems to be Solved by the Invention) A drawback of the conventional array-type infrared detector described above is that the dark resistance between each detection element is not uniform. In such a configuration, the dark resistance of each element is the resistance between the p-side electrode 7 and each n+ side electrode 6. If the resistance of the electrode is ignored, this is the original resistance of the sensing element itself, that is, the resistance of the n + p junction and the p resistance between the p-side electrode 7 and the n + p junction.
It is clear that the resistance is the sum of the resistances of the HCo, acdo, and 2Te layers 2. The former is uniform between each element in an ideal case, but the latter increases in proportion to the distance between each element and the p(!l electrode 7. If the resistance of the n+p+ combination is sufficiently large, the latter can be ignored. For example, Semiconductors and Semi-Metals Volume 18 (5ernicondu
ctors and semi-metals vol.
, 10 (1981) Academic Press), the narrow forbidden band width 11gg, g
With materials such as cdg and 2Te, it is impossible to increase the resistance of an n+p+ combination. For example, in the case of an n+p+ combination with a diameter of about 100 μm, the resistance may be on the order of several Ω.

On the other hand, although the resistance due to the p-type Hgo, GCDG, and 2Te layers 2 depends on the shape of the p-side electrode 7, it also becomes Ω when the distance between the junction of the p@electrode 7 and n becomes about 2C11.

Therefore, in an array type infrared detector having a total size of about 2C11, the non-uniformity of the dark resistance of each element due to this cannot be ignored, and as a result, output signal processing from each detection element becomes complicated.

In order to eliminate the above drawbacks, it is necessary to remove the p-side electrodes 7 from as many parts of the array as possible.

However, when considering a two-dimensional array type infrared detector, for example, if the p-side electrode 7 is taken from between the arrays, the structure becomes quite complicated, so it is preferable to take the p-side electrodes 7 from the ends of the two-dimensional array. Therefore, this drawback is particularly problematic in the case of a two-dimensional array type detector.

An object of the present invention is to provide an array type infrared detector with uniform dark resistance without complicating the wiring.

(Means for Solving the Problem) In order to solve the problem, in the array type infrared detector of the present invention, a first semiconductor layer having a narrow forbidden band width and high carrier concentration is formed on the substrate. , is the same substance as this,
A second semiconductor layer having the same conductivity type and lower carrier concentration than the first semiconductor layer is sequentially formed, photodiodes serving as an infrared detection section are arranged in the second semiconductor layer, and each photodiode The feature is that one of the two electrodes for operating this is taken out individually from each of the photodiodes, and the other is taken out from the first semiconductor layer in common for all the photodiodes in the array. have

(Function) The structure of the present invention is such that the same highly doped semiconductor layer is interposed between the substrate and the semiconductor layer with a narrow bandgap in which the infrared detection section is to be manufactured, and the common electrode of the photodiode serving as the detection section is connected to the substrate. is extracted from this highly doped semiconductor layer. The electrical resistance of this layer is much smaller than that of the semiconductor layer used to manufacture the sensing part, so even in large-area array type detectors, the resistance from the common electrode to each sensing element can be reduced.
Eventually, the dark resistance of each sensing element becomes uniform.

(Example) Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the present invention. In the figure, 1 is a CdTe substrate, 2 is a p+ type layer epitaxially grown on it, that is, a p-type 11Ko, ca, zTe layer with a high acceptor concentration, and 3 is a p-type 111co, BCd6. zTe layer, 4
is the p-type 11go0gCdg, an n+ layer formed on zTeTe by a method such as ion implantation, and 5 is 5i02
6 is an electrode on the n++ side, 7 is an electrode on the second layer side, 8 is a signal processing unit such as a silicon COD, and 10 is an infrared light incident on the detector. The sensing element itself is a photodiode that utilizes a four-layer junction under the n+ layer 4, and is arranged in the same way as shown in FIG. At this time, the n+ side electrode 6 is taken from each element, but the P side electrode 7 is p-type l1io, 8cd,,z
A portion of the Te layer 2 is removed and the 24 layers 3 below it are taken.

-m, in order to improve the characteristics such as the sensitivity of the single photodiode obtained, p-type 11g□, gCdo, 2T
The acceptor concentration of the e-layer 2 is approximately 1016C1l-'. In contrast, the acceptor concentration in layer 3 of 24 is 10”
When C11-' or more, the resistivity of 24 layers 3 is 9 layers 2
It was possible to reduce the value to 1710 or less. Therefore, 24
If the p-side electrode of each photodiode is shared through the layer 3, the resistance from the p1m electrode 7 to each photodiode is the second
We were able to make it extremely small compared to the case shown in the figure. Therefore, the dark resistance of each sensing element in the array approaches the resistance of the net n+p junction, so the dark resistance becomes uniform.

Furthermore, another effect of the present invention is an increase in the dark resistance of each sensing element. In this configuration, each sensing element is not a simple n+p junction photodiode, but an n''pp+ junction.
s and 5ernirnetals vol, 1B
(1981) Academic Press), the diffusion current, which is a component of the dark current, decreases. Therefore, when most of the dark current is due to diffusion current, the dark current of each photodiode decreases,
Dark resistance increases. Since the dark resistance of a single sensing element increases in this way, the contribution of the resistance from the p-side electrode 7 to each sensing element becomes even smaller, and the uniformity of the dark resistance is further improved.

(Effects of the Invention) As explained above, the present invention improves the uniformity of dark resistance in an array type infrared detector by reducing the resistance from each arrayed photodiode to its common electrode. It is what makes it possible. Therefore, it is possible to obtain an array type infrared detector whose output signal processing is easy.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a sectional view of an array-type infrared detector according to an embodiment of the present invention, and Fig. 2 is a sectional view of an example of an array-type infrared detector having a conventional structure. . In the figure, 1 is a CdTe substrate, 2 is a p-type I1g□,
gcdg, 2Te layer, 3 is p+ type Hgo, BCd6
．． 2Te layer, 4 is 4 layers, 5 is insulating film, 6 is n+ side electrode, 7 is p side electrode, 8 is silicon CCD chip
rework

Claims (1)

[Claims] In an array type infrared detector, a first semiconductor layer having a narrow bandgap and a high carrier concentration is formed on the substrate, and the first semiconductor layer is made of the same material, has the same conductivity type, and has a higher carrier concentration than the first semiconductor layer. A second semiconductor layer with a low temperature is sequentially formed, and photodiodes serving as an infrared detection section are arranged and formed in the second semiconductor layer, and in each photodiode, one of the two electrodes for operating the photodiode is formed. is taken out from each of the photodiodes individually, and the other is taken out from the first semiconductor layer in common for all the photodiodes in the array.