JPS6143647B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an infrared sensing element whose basic structure is a metal-insulator-semiconductor diode (hereinafter abbreviated as MIS diode). This invention relates to the structure of an infrared sensing element that can be realized without adding special impurities only to the recombination layer by forming the bonding layer with a heterojunction configuration caused by the agreement of the compositions of multiple semiconductors. .

The first MIS structure photodetector for visible light
As shown in the figure, the surface layer 3 of the semiconductor substrate 1 made of silicon or the like directly under the insulating film 5 is made p-type, and the deep layer below the surface layer 3 of the substrate is made p-type. The substrate 2 is doped with impurities at a high concentration, so that even if long wavelength light is transmitted deep into the substrate 1 and generates carriers, it is immediately recombined. If such a recombination layer is not formed, the generated carriers will diffuse in the substrate semiconductor and will be formed in the surface layer 3 by, for example, a positive voltage applied to the electrode 6 via the terminal 7. Potential well (hereinafter simply referred to as well)
8 and mix with the charge in the well, causing crosstalk and impairing resolution.

In addition, a charge injection device (hereinafter referred to as CID) is a typical example of a device whose basic structure is an MIS diode.
), if the carriers injected into the substrate directly under the insulating film are not eliminated by recombination within a short period of time, the frequency response characteristics will deteriorate.

As described above, in a photodetector having an MIS structure for visible light, the recombination layer shown as the deep layer 2 can be formed by diffusion of impurities, so no problem occurs. However, it is extremely difficult to adopt such a structure in an MIS configuration whose target is infrared detection. The reason for this is that multi-component semiconductors with a narrow band width are used as semiconductor materials for infrared sensing elements, but such multi-component semiconductors generally have very large impurity diffusion coefficients, and the high concentration of impurities in the recombination layer It immediately spreads to the surface layer 3. For this reason, it has been difficult to construct a recombination layer and reduce the thickness of the surface layer 3 to such an extent that sufficient recombination can be achieved.

The present invention has been made in view of these drawbacks, and is an infrared sensing element that uses a multi-component semiconductor as a substrate and has an MIS diode as its basic structure. At the same time, the surface layer of the semiconductor substrate separated by the heterojunction is made of a multi-component semiconductor with a narrow forbidden band width, and the deep layer in contact with the surface layer is made of a quasi-metallic layer. The present invention aims to provide an infrared detector characterized in that carriers are recombined in a metal layer, and will be described in detail with reference to FIG. 2 and subsequent drawings.

FIG. 2 shows one embodiment of the infrared detecting element according to the present invention, and the same parts as in FIG. 1 are designated by the same reference numerals. To make such an infrared sensing element, first, on an epitaxial growth substrate 9 made of cadmium tellurium ₍ CdTe), a layer made of the quasi-metal Hg _0.9 Cd _0.1 Te, that is, a deep layer 4, is deposited to a thickness of, _for example, 5 μm. Epitaxially grown to a thickness of . And above that, there is a forbidden band width
A layer made of Hg _0.7 Cd _0.3 Te of 0.25 ev, that is, the surface layer portion 3 _, is also epitaxially grown to a thickness of, for example _, about 10 μm.

In this way, the quasi-metal deep layer 4 and the narrow forbidden band width surface layer 3 are grown on the epitaxial growth substrate 9, for example, in a mercury atmosphere.
Heat treatment is carried out at a temperature of 400℃. In the surface layer portion (Hg _0.7 Cd _{0.3 Te} ) shown as 3, metal site vacancies occur at a density of, for example, 2 _× 10 ¹⁵ cm ^-3 and an equilibrium state is reached. Incidentally, the vacancies in the metal sites mentioned above act as acceptor impurities.

Therefore, if no foreign impurities are doped during the growth of the deep layer 4 and the surface layer 3 using epitaxial technology, the actual impurity concentration of the surface layer 3 will be N _A −N _D =2× 10 ¹⁵ cm ^-3 .
However, N _D is the donor concentration and N _A is the acceptor concentration.

In this way, the deep layer 4 and the surface layer 3 become a quasi-metallic layer and a low impurity concentration p-type semiconductor layer, respectively, and it goes without saying that the deep layer 4 formed of this quasi-metallic layer becomes a recombination layer. .

The deep layer 4 and the surface layer 3 are grown on the CdTe substrate 9 in this way, and then an insulating film 5 is disposed on top of the insulating film 5, and a transparent film such as nickel (Ni) is further applied to a thickness of about 200 Å on top of the insulating film 5. If an electrode 6 is provided by vapor deposition, a photosensitive MIS diode is completed. However, in this infrared detector, light can be blocked by forming, for example, aluminum (Al) of about 8000 Å in areas that are not light-detecting parts.

Figure 3a shows the insulating film 5 by lowering the potential surface 11 of the conductive electrode of the MIS diode made in this way.
A band diagram is shown in which an inversion layer 13, that is, a potential well is provided on the semiconductor side of the semiconductor, and carriers (electrons in this case) generated by photoelectric conversion are accumulated in the well.

On the other hand, in FIG. 3b, the potential plane 11, which has been lowered until now, is raised to form a cumulative layer 15 on the semiconductor side of the insulating film. is pushed to the right as shown by arrow A. This is the injection of carrier into the substrate. However, the surface layer 3
Since the right end of is adjacent to the deep layer 4 and forms a slope of potential, the carrier flows into the deep layer 4 as shown by the arrow (b). However, since the deep layer 4 is formed of a quasi-metallic layer as described above, the carriers (electrons) are recombined with carriers (holes) of opposite polarity and disappear, as shown by arrow C. In Figure 3, E _C is the bottom of the conduction band, E _V is the top of the valence band, and E _F is the Fermi level.

The case where the multicomponent semiconductor forming the surface layer portion 3 is p-type has been described above. The multicomponent semiconductor forming the surface layer 3 was made p-type as a result of increasing the concentration of vacancies in the metal sites that function as acceptors.

However, the above-mentioned multicomponent semiconductor may be of n-type, and can actually be of n-type. For this purpose, aluminum (Al) or indium (In), for example, is used as an impurity for doping. In this way, Al or In is
In order to act as a donor in HgCdTe, the Fermi level E _F approaches the bottom E _C of the conduction band in the surface layer 3 composed of the above multi-component semiconductor, and the surface layer 3
Make it n-type. However, since the deep layer 4 is a quasi-metal from the beginning, the conductivity type does not reverse as described above, and in this case as well, it acts as a quasi-metal.

FIG. 4a shows an inversion layer 13, that is, a potential well, by pulling up the potential surface 11 of the conductive electrode of the MIS diode whose surface layer 3 is an n-type multi-component semiconductor made in this manner. carriers (holes in this case) generated by photoelectric conversion.
This shows a band diagram showing the state in which .

On the other hand, in FIG. 4b, the potential surface 11, which has been raised until now, is lowered to form a cumulative layer 15 on the semiconductor side of the insulating film. The carrier is pushed to the right in the direction shown by arrow A, and the carrier is injected into the substrate. However, the right end of the surface layer 3 forms a potential slope adjacent to the deep layer 4 where no forbidden band width can be drawn because it is a quasi-metal.
The carriers flow into the deep layer 4 as shown by the arrow (b), and disappear by recombining with carriers of opposite polarity, that is, electrons, as shown by the arrow (c).

As described above, the structure of the infrared sensing element according to the present invention has the feature that it can be applied regardless of the conductivity type of the surface layer, and the carrier recombination layer shown as the deep layer is not doped with foreign impurities. Since the surface layer is not contaminated with impurities, great practical effects can be expected.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the structure of a conventional infrared detector used for visible light, Fig. 2 is a diagram showing the structure of an infrared detecting element according to the present invention, and Figs. 3 a and b are diagrams showing the above-mentioned infrared detecting element. Figures 4a and 4b are diagrams showing the carrier accumulation and injection operations when the surface layer of the infrared sensing element is of the n-type. It is. 1: Semiconductor substrate, 3: Surface layer of the substrate, 4: Deep layer of the substrate, 5: Insulating film, 6: Electrode, 7: Terminal,
8: Potential well, 13: Inversion layer, 15: Accumulation layer.

Claims (1)

[Claims] 1. In an infrared sensing element that uses a multi-component semiconductor as a substrate and has an MIS diode as its basic structure, a multi-component semiconductor heterojunction in which a semiconductor to quasi-metallic transition occurs depending on the composition is formed on the semiconductor substrate, and the heterojunction By making the surface layer part of the semiconductor substrate to be separated a multi-component semiconductor with a narrow forbidden band width, and making the deep layer part in contact with the surface layer part a quasi-metal layer,
An infrared sensing element characterized in that carriers are recombined in the quasi-metallic layer.