RU2488916C1 - Semiconductor infrared detector - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: semiconductor infrared detector includes a semiconductor substrate (1) AIIIBV with an active region (2) in form of a disc with a hole in the centre based on a heterostructure made from solid solutions AIIIBV, a first ohmic contact (4) and a second ohmic contact (7). The first ohmic contact (4) is deposited on the surface (3) of the active region (2). The second ohmic contact (7) is deposited on the surface (6) of the peripheral region (8) of the semiconductor substrate (1), lying opposite the surface with the active region (2). There is at least one depression (10) in the surface (6) of the central region (9) of the semiconductor substrate (1) free from the second ohmic contact (7).

EFFECT: invention enables to make a semiconductor infrared detector which, along with a wider spectral sensitivity region in the middle infrared region of 2-5 mcm, has high quantum efficiency and lower density of backward current.

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Description

The invention relates to optoelectronic technology, more specifically to compact radiation photodetectors in the infrared (IR) wavelength range, used in various fields of science and technology, in industry, namely in spectroscopy, medicine, optical communication systems and information transfer, in optical superfast computing and switching systems.

A feature of photodiodes (PD) for the mid-IR region of the spectrum (3-5 μm) operating at room temperature is the relatively weak quantum efficiency (20–40%).

Known semiconductor receiver (see patent US 3542477, IPC G01S 1/02, published 24.11.1970), comprising a housing with a window behind which is a hemispherical concave mirror directing radiation to the photodiode.

The disadvantages of the known design include the exposure of the mirror to environmental influences during operation, such as mechanical, chemical and thermal. In addition, a hemispherical mirror is difficult to manufacture and rather bulky.

Known semiconductor infrared detector (see US 2010320552, IPC H01L 31/00 published December 23, 2010), consisting of a substrate, a photodiode formed on a substrate in which the interacting parts are separated from one another by dielectric material. The luminous flux penetrates at least through part of the dielectric material. A microlens is located above the luminous flux, and even higher is a color filter.

The disadvantages include the fact that in the known infrared receiver, external devices (microlenses, light filters) are used, complicating its design.

Known immersion detector of infrared radiation (see R. Clark Jones. - "Immersed radiation detectors". - Appl. Opt., 1, p.607-613, 1962), in which the sensitive element is in optical contact with the lens with a high index refraction.

When using lenses, achieving high sensitivity values for wavelengths of 3-5 μm at room temperature is often accompanied by obtaining a narrow angle of view of the photodiode determined by the geometry of the lens and a narrow sensitivity band (with a half-width of the spectrum of ~ 0.6 μm, which does not satisfy the requirements of some applications).

Known semiconductor infrared detector based on InAs / InAs _0.88 Sb _0.12 / InAsSbP heterostructures for the spectral range of 2.5-4.9 μm (see Sherstnev V.V., Starostenko D., Andreev I.A., Konovalov G., Ilyinskaya N.D., Serebrennikova O.Yu., Yakovlev Yu.P. - PZhTF, 2011, vol. 37, v. 1, pp. 11-17). The density value of the reverse dark currents of such PDs is (1.3-7.5) · 10 ^-2 A / cm ² at a reverse bias voltage of 0.2 V. The differential resistance at the bias zero reaches 700-800 Ohms.

But such infrared detectors are characterized by insufficiently high sensitivity, which at the maximum of spectral sensitivity is (5-8) · 10 ⁸ cm · Hz ^½ · W ^-1 .

Known semiconductor infrared detector (see application US 2004171183, IPC H01L 21/00, H01L 31/00, published 02.09.2004), consisting of a semiconductor substrate and sequentially deposited on it a buffer and light-absorbing layers. An epitaxial layer containing an active region in the form of a convex lens is formed of InP on the upper surface of the light-absorbing layer. A dielectric layer is formed on the upper surface of the epitaxial layer, excluding the active region. The first p-type metal electrode is formed on the upper surface of the dielectric layer, the second n-type metal electrode is formed on the lower surface of the substrate. The buffer layer consists of a crystalline structure identical to the structure of the substrate.

A key element of the known photodiode is a convex lens located inside the semiconductor crystal in the active region of indium phosphide (InP). Such material is sensitive to radiation in the visible and near infrared range, but cannot be used for use in the average infrared range (2-5) microns.

A well-known semiconductor receiver of infrared radiation (see. Letters in ZhTF, volume 37, issue 19, pages 95-103, 2011), which coincides with the claimed solution for the largest number of essential features and adopted as a prototype. A known semiconductor infrared detector includes an InAs semiconductor substrate with a ring active region based on a heterostructure made of InAsSb solid solutions, a first ohmic contact deposited on the surface of the ring active region, and a second solid ohmic contact deposited on the entire surface of the semiconductor substrate, an opposite surface with a ring active region.

The advantage of the well-known semiconductor receiver prototype is the extended range of spectral sensitivity in the average IR range (2-5) microns. However, the known semiconductor receiver has insufficient quantum efficiency, and a high density of reverse currents.

The present invention was the development of such a semiconductor infrared radiation detector, which, along with an extended spectral sensitivity range in the mid-IR range (2-5) microns, had an increased quantum efficiency and lower density of reverse currents.

The problem is solved in that the semiconductor infrared detector includes an III – V semiconductor substrate with a disk shaped active region with a hole in the center based on a heterostructure made of III – V solid solutions, a first ohmic contact and a second ohmic contact. The first ohmic contact is applied to the surface of the active region. A second ohmic contact is applied to the surface of the peripheral region of the semiconductor substrate, the opposite surface with the active region. New is the implementation in the surface of the semiconductor substrate, free from the second ohmic contact, at least one recess.

The surface area of the substrate through which incident light penetrates into the crystal should be significantly larger than the area of the active region in the form of a disk with a hole in the center based on a heterostructure made of III – V solid solutions.

The recess can have any round-curved surface (spherical, elliptical, parabolic).

Preferably, the recess may have a depth h satisfying the relationship:

λ <h <d, μm,

where λ is the wavelength of the incident light with an energy equal to the band gap of the active region of the semiconductor infrared detector, microns;

d is the thickness of the substrate, microns.

Preferably, the recesses are made over the entire surface of the semiconductor substrate, free from the second ohmic contact. In this case, the recesses can be made both close to each other, and to stand apart from each other.

It was found that this semiconductor receiver, along with an extended spectral sensitivity range, has increased quantum efficiency in the mid-IR region of the spectrum (2-5) microns due to the additional absorption in the active region of the heterostructure of photons repeatedly reflected from the curved surfaces of the recesses in the semiconductor substrate .

The expansion of the sensitivity spectrum of a semiconductor receiver based on narrow-gap semiconductor compounds can be achieved either through thin substrates or through the use of heavily doped n-type substrates with degeneration of electrons in the conduction band, in which the absorption edge is shifted due to the Moss-Burshtein effect into the short-wave region of the spectrum (see E. Burstein. - Phys. Rev., v. 83, p. 632, 1954). The present invention is illustrated in the drawing, where:

figure 1 shows a top view of a semiconductor receiver prototype;

figure 2 shows a cross section along aa of the semiconductor receiver of the prototype shown in figure 1;

figure 3 shows a top view of the semiconductor receiver of the present invention;

FIG. 4 is a cross-sectional view along BB of one embodiment of the semiconductor receiver shown in FIG. 3;

5 is a cross-sectional view of another embodiment of a semiconductor receiver;

6 is a bottom view of another embodiment of a semiconductor receiver of the present invention;

7 is a bottom view of another embodiment of the semiconductor receiver of the present invention;

Fig. 8 shows the photoresponse spectra at a temperature T = 300 K of InAs semiconductor receivers of three variants: 1 — prototype semiconductor receiver (continuous ohmic contact on the back of the substrate); 2 - ohmic contact is located outside the Central region of the substrate with a diameter of 880 microns; 3 - semiconductor receiver of the present invention (the central region of the substrate with a diameter of 880 μm is filled with etched hemispheres with a diameter of 60 μm in depth;

figure 9 shows the spectra of the photoresponse at a temperature T = 300 K of GaSb-based semiconductor detectors of three options: 4 - prototype semiconductor receiver (continuous ohmic contact on the back of the substrate); 5 - ohmic contact is located outside the Central region of the substrate with a diameter of 880 microns; 6 - semiconductor receiver of the present invention (the Central region of the substrate with a diameter of 880 μm is filled with etched hemispheres with a diameter of 60 μm in depth).

The semiconductor infrared detector of the present invention (see FIG. 3, FIG. 4) includes an AIIIBV substrate 1 on which a disk-shaped active region 2 is grown with a hole in the center based on a heterostructure made from AIIIBV solid solutions. On the surface 3 of the annular active region 2 in its middle part, the first ohmic contact 4 is formed. In contrast to the semiconductor receiver prototype (see FIG. 1, FIG. 2), in which the second ohmic contact 5 is applied to the entire surface 6 of the semiconductor substrate 1 opposite the surface 3 of the annular active region 2, in the semiconductor infrared detector of the present invention (see figure 3 - figure 4), the second ohmic contact 7 is applied only to the surface 6 in the peripheral region 8 of the semiconductor substrate 1, and on top 6 the central spine region 9 of the semiconductor substrate 1, free from the second ohmic electrode 7, comprises at least one recess 10 (see FIG. 4). The greatest effect is achieved when the recesses 10 are made in the entire surface 6 of the Central region 9 of the semiconductor substrate 1, free from the second ohmic contact (see figure 5). In this case, the recesses 10 can be made both close to each other (see Fig.6), and to defend from each other (see Fig.7). The recesses 10 may be the same or different size.

Example. 1. The manufacture of a semiconductor infrared detector of the present invention can be illustrated by the example of a heterostructure, for example, the composition InAs / InAs _0.94 Sb _0.06 / InAsSbP / InAS _0.88 Sb _0.12 / InAsSbP. The heterostructure was grown by liquid-phase epitaxy (LPE) on a substrate with a thickness of 200 μm n-InAs orientation [100] doped with tin to a carrier concentration of 5 × 10 ¹⁸ cm ^-3 . In such a substrate (see BAMatveev, M. Aydaraliev, NVZotova, SAKarandashev, MARemennyi, NMStus, GNTalalakin. - Proc. SPIE, 4650, 173, 2002), the fundamental absorption edge shifts to the short-wavelength region of the spectrum (Moss - Burshtein shift), and it becomes transparent to radiation with a wavelength greater than 2.5 μm formed in the active region of the structure. On the substrate, a wide-gap InAsSbP emitter layer of 6.2 μm thick, an InAsSb active layer of _0.12 2.5 μm thick, intentionally undoped (n ~ 1 × 10 ¹⁵ cm ^-3 ), and a wide-band InAsSbP solid-state emitter layer of thickness 1 were successively grown on a substrate , 4 microns, doped with zinc to P = 2 × 10 ¹⁸ cm ^-3 . To reduce the deformation of the active region between the layers and the substrate, an InAsSb _0.06 layer with a thickness of 3.3 μm was grown. The wide-band InAsSbP emitter layer and the InAsSb _0.06 layer were obtained of the N type by doping with Sn (tin) to a level of 5 × 10 ¹⁷ cm ^-3 , while the wide-gap P-InAsSbP window was doped with Mn (manganese) to a concentration of P = (2 -5) × 10 ¹⁷ cm ^-3 . Chips in the form of a square with a side of 950 μm were formed on the epitaxial layer by the method of photolithography and etching on the grown structure, on each of which an active region in the form of a disk with a hole in the center was formed. The outer diameter of the disk is 770 μm, the diameter of the hole is 600 μm, and the height measured from the upper epitaxial layer is 18 μm. Outside the disc with the hole, i.e. inside and out, the heterostructure was etched to the substrate. The area of the sensitive area was 0.1 mm ² . The three-layer first ohmic contact of the Cr / Au-Ge / Au composition, with an external radius of 350 μm and a width of 15 μm, was located in the middle of the disk with the hole. Thus, only part of the radiation incident on the front surface of the chip was absorbed by the disk structure, and the rest of the radiation incident on the outside of the disk freely penetrated the transparent substrate for radiation and reached the back of the chip. After spraying multilayer contacts, the structure was heat treated in a hydrogen medium to form the first and second ohmic contacts. Then, the chips were mounted on the substrate side on a standard case for mounting TO-18 semiconductor chips to conduct studies of the electrical and photoelectric characteristics at T = 300 K of the created semiconductor infrared radiation detectors. The resistance Ro of semiconductor receivers at the bias zero was measured in the range (+10 mV) ÷ (-10 mV) and amounted to R ₀ = 5-30 Ohms for the receivers considered below. To study the sensitivity spectra of semiconductor infrared detectors, we used the SPM2 monochromator (Carl Zeiss). The measurements were carried out according to a synchronous detection scheme using a Stanford Research SR830 instrument.

From one heterostructure using contact photolithography and liquid chemical etching, three versions of a semiconductor infrared detector were created. The scheme of the first option (receiver-prototype) is shown in figure 1 - figure 2. The circuit of the semiconductor infrared receiver of the present invention is shown in figure 3, figure 5. The third option was different from the infrared receiver of the present invention, shown in figure 3, figure 5, the absence of recesses on the back of the substrate. On the epitaxial layer side, all three types of receivers were identical. In the semiconductor prototype receiver, the second ohmic contact to the n-InAs substrate consisted of Cr / Au-Te / Au layers successively deposited by thermal vacuum spraying and completely covered the substrate surface of the 950 × 950 μm ² photodiode chip. This is the so-called continuous contact, traditionally used in the manufacture of optoelectronic devices. Consider how the light fluxes are distributed for each of the three types of semiconductor infrared detectors. For the first version of the semiconductor infrared detector (prototype), the light flux passing through the hole of the disk falls on the substrate with the second solid ohmic contact deposited externally and is mainly absorbed at the substrate - second ohmic contact interface in the eutectic region. (This is confirmed by the nature of the photoresponse spectra in Fig. 8, curve 1.). The second variant of the semiconductor infrared detector was different from the first in that the second ohmic contact was applied to the surface of the peripheral region of the semiconductor substrate, while the central region of the substrate with a diameter of 880 μm was free from metallization. In the second version of the receiver, the light flux passing through the hole of the disk, falls on the surface of the substrate, free from the second ohmic contact. In this case, part of the radiation is reflected to a greater extent from the nonmetallized central region of the substrate and is partially absorbed by the active region in the form of a disk with a hole in the center, contributing to the increase in the photocurrent of the receiver (see Fig. 8, curve 2). However, in this case, the light flux cannot change the angle of incidence and reflection from the surface of the substrate. The third variant of the semiconductor infrared detector (according to the present invention) differed from the two previous versions in that, in the surface of the central region of the semiconductor substrate, free of the second ohmic contact, grooves were made in the form of hemispheres 60 μm deep, made by liquid chemical etching. In the third embodiment of the semiconductor infrared detector, the light flux passing through the hole of the disk falls on the surface of the substrate in which the recesses are made. Reflecting from the curved non-metallic surface of the substrate formed by the recesses, the light fluxes after repeated reflection change their directions in the substrate and are mainly either absorbed in the active region of the disk or extend beyond the substrate (see Fig. 8, curve 3).

In the case of one recess (with the same dimensions), the sensitivity increases by 1.05 times.

Example 2. The manufacture of a semiconductor infrared detector of the present invention can also be illustrated by the example of a heterostructure, for example, the composition of GaSb / Ga _1-x In _x AS _y Sb _1-y / Ga _1-x Al _x AS _y Sb _1-y . The heterostructure was grown by liquid phase epitaxy (LPE) on a substrate with a thickness of 200 μm n-GaSb orientation [100], doped with tellurium to a carrier concentration of ~ (1-5) · 10 ¹⁷ cm ^-3 . Chip fabrication and measurements were carried out similarly to those described above for InAs. We studied photodiodes with a spectral sensitivity range of 1.5–2.5 μm. The response spectra are shown in Fig.9.

The measurements showed that the implementation of the recesses in the surface of the Central region of the semiconductor substrate allows you to redistribute the radiation fluxes in the structure and increase the effective area for the collection of radiation. This is evidenced by the results of measuring the photoresponse of the investigated semiconductor infrared radiation detectors. The sensitivity increases by 1.3-1.7 times in comparison with the semiconductor receiver prototype. Correspondingly, the quantum efficiency of the conversion of radiation into a photo library increases, which manifests itself in an increase in the photo signal from the photodiode when the photodiode is illuminated with light of this spectral range.

Claims (6)

1. A semiconductor infrared detector including an III – V semiconductor substrate with a disk-shaped active region with a hole in the center based on a heterostructure made of III – V solid solutions, a first ohmic contact deposited on the surface of the active region, and a second ohmic contact deposited on the peripheral surface the area of the semiconductor substrate, the opposite surface with an active region, while in the surface of the Central region of the semiconductor substrate, free of the second ohmic one contact has at least one recess. 2. The semiconductor receiver according to claim 1, characterized in that in the entire surface of the Central region of the semiconductor substrate, free from the second ohmic contact, recesses are made. 3. The semiconductor receiver according to claim 2, characterized in that the recesses are in contact with each other. 4. The semiconductor receiver according to claim 2, characterized in that the recesses are spaced from each other. 5. The semiconductor receiver according to claim 1, characterized in that the surface of the recess has a curved surface. 6. The semiconductor receiver according to claim 1, characterized in that the recess is made with a depth h satisfying the ratio:
λ <h <d, μm,
where λ is the wavelength of the incident light with an energy equal to the band gap of the active region of the semiconductor infrared radiation receiver, μm;
d is the thickness of the substrate, microns.

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