JPH0770697B2 - Array type infrared detector - Google Patents

Description

The present invention relates to an array type infrared detector, and more particularly to an array type infrared detector using a semiconductor having a narrow bandgap.

[Prior Art] It is generally known that an infrared detector using a semiconductor with a narrow bandgap has high sensitivity. In particular, a detector having a configuration in which single detector elements are arranged in one dimension or two dimensions is very effective when used in an infrared imaging device.

As a configuration of a conventional array type infrared detector, as shown in SPI (SPIE Vol. 443, 1983 page 120), only the infrared detector uses a semiconductor with a narrow bandgap, A hybrid structure is known in which this is connected to a signal processing unit such as a silicon CCD (charge coupled device).

FIG. 2 is a sectional view showing an example of a conventional array type infrared detector.

In the figure, the structure of the conventional array type infrared detector is Cd.
Te substrate 11, Hg _0.8 Cd _0.2 Te layer 2, Hg _0.8 Cd _0.2 Te photodiode 2, which is an infrared detector formed on Te layer 2, indium pillar
12, a signal processing chip including a silicon CCD 13, and a charge signal injection layer 14 to the signal processing unit. In this structure, Hg _0.8 Cd epitaxially grown on CdTe substrate 11 is used.
Infrared detector is formed in _0.2 Te layer 2 and CdTe substrate 1
Infrared light 20 is incident from one side, and an electric signal as its output is input to the silicon CCD 13 through the indium column 12. As a result, the signals from the arrayed infrared detectors are read out to the outside through the silicon CCD 13.

[Problems to be solved by the invention]

The above-mentioned conventional array-type infrared detector requires an extremely difficult process of connecting Hg _0.8 Cd _0.2 Te and silicon with an indium pillar in manufacturing thereof. Furthermore, this array type infrared detector is usually used after cooling to about 77k, but during repeated use, due to the difference in thermal expansion coefficient between Hg _0.8 Cd _0.2 Te and silicon, A disconnection occurs at the connecting portion between the two, that is, at the indium pillar. As the number of elements arranged increases, the number of connections also increases, and therefore the reliability of the array type infrared detector becomes low.

Further, since silicon and indium are not transparent to infrared rays, it is clear that the configuration shown in FIG. 2 can be used only by making infrared rays incident on the infrared detecting section from below. In the case of FIG. 2, a CdTe substrate 11 is used as a substrate for epitaxial growth of the Hg _0.8 Cd _0.2 Te layer 2, and the CdTe substrate 11 has a wavelength of 10 to be detected by the Hg _0.8 Cd _0.2 Te layer 2.
Such a configuration is possible because it is transparent to infrared rays of about μm.

However, in recent years, advances in epitaxial growth technology for Hg _1-x Cd _x Te crystals have made it possible to grow high-quality Hg _1-x Cd _x Te on substrates other than CdTe, for example, with sapphire. In this case, there is a limitation that the configuration shown in FIG. 2 cannot be taken unless the substrate is transparent to infrared rays to be detected. 10 μm when sapphire is used
Since the infrared light in the band does not pass through this, it is impossible to take the configuration shown in FIG.

Without connecting the silicon CCD13 chip to the infrared detector, the silicon CCD13 is also on the same semiconductor as the detector, that is, Hg _0.8 Cd
Forming it on the _0.2 Te layer 2 solves these problems.
However, when silicon is used, a high-performance CCD can be manufactured, whereas when Hg _0.8 Cd _0.2 Te is used, it is extremely difficult to obtain a high-performance CCD.

An object of the present invention is to provide a highly reliable wiring type infrared detector which can be used by making infrared light incident from the side opposite to the substrate.

[Means for solving problems]

In the array type infrared detector of the present invention, a first semiconductor layer of Hg _1-x Cd _x Te layer is formed on an epitaxially grown substrate, and Hg _1-y Cd _y Te is further formed on the first semiconductor layer. Layer (0 <x <y
The second semiconductor layer of <1) is formed, the second semiconductor layer is partially removed, and the infrared rays incident on the first semiconductor layer are exposed to the exposed portion of the first semiconductor layer. An infrared detector for converting into an electric signal is formed, and a signal processor for processing the electric signal is formed in the second semiconductor layer.

[Action]

According to the present invention, a semiconductor having a narrow bandgap is grown on an epitaxial growth substrate, and a semiconductor having a wider bandgap is grown on the semiconductor. An infrared detector is formed on the former and a semiconductor is formed on the latter.
It forms a signal processing unit such as a CCD. For this reason, it is unnecessary to connect a silicon CCD because both the infrared detector and the CCD are formed on the same substrate, and it is possible to use infrared light incident from the side opposite to the substrate. There is no restriction that the epitaxially grown substrate must be transparent in order to be possible.

〔Example〕

 Next, an embodiment of the present invention will be described with reference to the drawings.

1 (a) and 1 (b) are a top view and a sectional view, respectively, showing an embodiment of the present invention.

In this figure, this example shows a substrate for Hg _1-x Cd _x Te epitaxial growth (hereinafter referred to as an epitaxial growth substrate) 1, Hg
_0.8 Cd _0.2 Te layer 2, Hg _0.3 Cd _0.7 Te layer 3, Hg _0.8 Cd _0.2 Te Photo diode 4, insulating layer formed on the layer 2, insulating film
5, indium electrode 6, charge signal injection layer 7 and Hg _0.3 Cd _0.7
It has a charge transfer gate 8, a charge storage gate 9, and a CCD 10 formed on the Te layer 3.

In this example, a Hg _0.8 Cd _0.2 Te layer 2 was first grown as a first semiconductor layer on an epitaxial growth substrate 1, and a Hg _0.3 Cd _0.7 Te layer 3 was formed as a second semiconductor layer on the Hg _0.8 Cd _0.2 Te layer 3. A structure formed by heteroepitaxial growth is used. By partially etching the Hg _0.3 Cd _0.7 Te layer 3, the Hg _0.8 Cd _0.2 Te layer 2 is exposed, and the photodiode 4 is formed by, for example, ion implantation in this portion. This is an infrared detector for the wavelength band of 10 μm determined by the forbidden band width of the Hg _0.8 Cd _0.2 Te layer 2. On the other hand, CCD10 was formed on the surface of the Hg _0.3 Cd _0.7 Te layer 3 left without etching.
An output signal processing unit such as
Connect with.

In this embodiment, the output signal processing unit including the CCD 10 is set to Hg _0.3
The reason for forming on the Cd _0.7 Te layer 3 will be described below.

In general, high-performance CCDs can be manufactured by using silicon, whereas high-performance CCDs can be manufactured by using Hg _0.8 Cd _0.2 Te.
Cannot be manufactured.

The greatest reason for this is described in, for example, Infrared Physics (Infrared Physics Vol. 20, 1980, page 1). According to this, in semiconductors with a narrow forbidden band such as Hg _0.8 Cd _0.2 Te, MIS (metal-
In the insulator-semiconductor structure, a tunnel current is generated when a voltage is applied to the gate. Therefore, the silicon CC
As in D, when the signal charge is stored or transferred under the gate electrode, the charge due to the tunnel current must be negligible compared to the signal charge. For this reason, only a voltage such that the tunnel current is sufficiently small can be applied to the gate.

The CCD principle is that the signal charge is accumulated and transferred in the potential well in the depletion layer under the gate, and this means that the amount of signal charge that can be handled is small. Therefore, it is very difficult to manufacture a CCD that can efficiently process the signal charge from the detector with a material having a narrow bandgap such as Hg _0.8 Cd _0.2 Te.

On the other hand, in the case of Hg _1-x Cd _x Te, which is a mixed crystal semiconductor as in this example, the band gap changes depending on its x value, and when x = 0.2,
It is 0.1eV, while 1eV when x = 0.7
It is about the same as silicon. Therefore, Hg _0.8 C
Compared to using d _0.2 Te, using Hg _0.3 Cd _0.7 Te gives MI
High-performance CCD can be manufactured without tunneling current in S manufacturing. Further, the smaller the x value is, the smaller the forbidden band width is. However, it is possible to manufacture a CCD that operates sufficiently though it is inferior to silicon when x is up to about 0.3.

Furthermore, when using a pn junction as the photodiode 4, it is important to coat the surface of the photodiode with an appropriate substance in order to suppress the surface leak current of the diode.
The Hg _0.3 Cd _0.7 Te layer 3 having a wider forbidden band than the Hg _0.8 Cd _0.2 Te layer 2 and having substantially the same lattice constant is suitable for this material. Therefore, according to the present embodiment, the photodiode 4, which serves as an infrared detector, also has a small leak current.

As described above, in this embodiment, by connecting the output signal processing unit including the photodiode 4 formed on the Hg _0.8 Cd _0.2 Te layer 2 and the CCD 10 formed on the Hg _0.3 Cd _0.7 Te layer 3, A high-performance array type infrared detector can be obtained. Furthermore,
In this configuration, since the infrared light 20 can be incident on the side opposite to the epitaxial growth substrate 1 and used, the epitaxial growth substrate 1 does not need to be transparent to the infrared light 20.

Hg ₁ -xCdxTe has a variable forbidden band (0 to 1.6 eV at a temperature of 77 ° K) by changing the value of x (mixed crystal ratio), and the photon energy equal to the energy of the forbidden band ( h
ν, ν; frequency of infrared light). Especially, when x is around 0.2, the band gap is about 0.1 eV,
This can be a detector for infrared light (thermal infrared light) having a wavelength of about 10 μm.

〔The invention's effect〕

As described above, according to the present invention, a semiconductor having a narrow bandgap is grown on an epitaxial growth substrate, and a semiconductor having a bandgap wider than this is further grown on the epitaxial growth substrate to form an infrared detector on the former and a semiconductor on the latter. Since the signal processing part such as CCD is formed, therefore, by forming both the infrared detection part and the CCD on the same substrate, there is no need to connect the silicon CCD chip and the infrared detection part, and There is no restriction that the epitaxial growth substrate of a semiconductor having a narrow bandgap for forming an infrared detecting portion to be used by allowing external light to enter from the side opposite to the epitaxial growth substrate should be transparent to infrared light. Therefore, a highly reliable and high-performance array type infrared detector can be obtained.

Especially, in the case of Hg _0.8 Cd _0.2 Te layer, the forbidden band width is 0.1e.
Since it is about V, it is effective to obtain an infrared light (thermal infrared) detector having a photon energy equal to this energy and a wavelength of about 10 μm.

[Brief description of drawings]

1 (a) and 1 (b) are a top view and a sectional view showing an embodiment of the present invention, and FIG. 2 is a sectional view showing an example of a conventional array type infrared detector. 1 …… Hg _1-x Cd _x Te substrate for epitaxial growth (epitaxial growth substrate) 2 …… Hg _0.8 Cd _0.2 Te layer, 3 …… Hg
_0.3 Cd _0.7 Te layer, 4 ... Photodiode, 5 ... Insulating film,
6 ... Indium electrode, 7 ... Charge signal injection layer, 8 ...
Charge transfer gate, 9 ... Charge storage gate, 10 ... CC
D, 11 …… CdTe substrate, 12 …… Indium pillar, 13 …… Silicon CCD, 14 …… Charge signal injection layer, 20 …… Infrared light.

Claims (1)

[Claims] 1. Hg _1-x Cd _x Te on an epitaxially grown substrate
A first semiconductor layer of a layer is further formed, and a second semiconductor layer of Hg _1-y Cd _y Te layer (0 <x <y <1) is further formed on the first semiconductor layer, and The second semiconductor layer is partially removed to expose the first semiconductor layer, and an infrared detector is formed to convert an infrared ray incident into the first semiconductor layer into an electric signal. An array type infrared detector characterized in that a signal processing unit for processing the electric signal is formed in the semiconductor layer of the above.