CS248690B1 - Bismuth telluride bismuth sulfide-telluride BigTe.RTM. - Google Patents

Abstract

The solution concerns new single-crystal structures with a P-N junction and a variable band gap. A method of preparing single-crystal structures of the composition bismuth telluride - sulfide - bismuth telluride BigTe^ -BigTe^xS-g from p-type BigTe^ crystals, pure or doped, is described in such a way that single-crystal plates with adjacent cleavage planes (0001) are exposed to sulfur vapors, the tension of which is 0.030 kPa - 150 kEa, at a temperature of 150 - 500 °C for 10-400 hours, or brought into contact with liquid sulfur at a temperature of 120 - 400 °C for 10-400 hours. By splitting the tempered plates along the (0001) surface, a P-N structure is obtained, which after making contacts exhibits a significant rectifying effect, characterizing a crystal diode and sensitivity to IC radiation.

Description

The invention relates to a method for preparing single-crystal structures, the composition of tellurium, bismuth - sulfide-telluride, bismuth ^Bi 2 ^Ie 3 ^"Bi 2 ^Te 3-x? X * ^kd ® ^XS θ · ⁰⁰¹ <t ≤ °> 4 sensitive to radiation in the infrared ·

Currently AE detectors ΐδ radiation which are based on semiconductors, using the following materials: silicon, germanium, compounds (especially InSb), compounds _A IVgVI _(P | js _j PbSe, PbTe) and the most significant appears to be a mixed crystal of Cd ^ Jlgj ^ Te.

So far, a process for preparing a PN 2 transition based on Bi ₂ Te _3e-x S _x has not been described.

Sulfur-doped Bi ₂ Te or BigTe-BigSi system has been addressed in a number of work relating to phase ai.gr, ™, _and Bi ₂ I. ₃ -a ₂ S ₃ / e.g. . G.Gmmberg, fcWauaann,

Helv. Phys. Acta 36, 810 (1963)], and the transport properties of compounds 2 ^Te 3-x ^S x / LA Kutasov, LNLukjanova, Piz. Tvěrd. body 24, 402 (1982)], or optical properties (P. Lošlák et al. Phys. State. Sol. (a) 8, K143 (1984)]. Unsubsidized and doped Bi2Te3 crystals have been studied since 1957, but only the discovery of a method of suppressing the concentration of antistructural disorders by polarizing bonds in AgBj ¹ crystals / J. Horák et al., Philos. Mag. B 50. 665 (1984)]. Based on this discovery, a method for obtaining a structure based on a compound Bi2Te _3e ^ S _x having a variable sulfur concentration on a single crystal and at the same time a PN transition, the preparation of which is the object of the present invention, is proposed.

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The object of the invention is a process for the preparation of monocrystalline structures of the composition bismuth telluride - bismuth sulfide-telluride BigTe ^{where xs} Ο, ΟΟΚΟ, Αι and a variable band gap width caused by a sulfur concentration gradient and a PN junction, characterized in that Pure or doped are exposed to sulfur vapors with a pressure of between 0.035 kPa and 150 kPa at

temperature 150 <5B0 ° C for 10aF foil hours, or contacted with liquid sulfur at 120 ° C for <400 hours ·

After this exposure, the crystals are cleaved along the area (0001) to give a BigTe-BigTe2S structure which, after suitable contacts can be used to construct crystal diodes.

The process starts from the single crystal p-BigTe® prepared by the Bridgman method from which monocrystalline plates are prepared by non-splitting according to areas (0001) _t showing good cleavability. These crystals are interacted with sulfur under the above conditions. On contact solid and gaseous, rsap. liquid algae occurs both on the growth of the crystal characterized by the reaction between sorbed sulfur molecules and antistructural disorders and on the other side the diffusion of the sulfur atoms into the crystal

1/2 S ₂ (g) + 2 Bij _e ♦ 2 h + 2 Ie ₂ ^ == ± S * ₀ + Bi ₂ Te ₃ , according to which the concentration of antistructural disorders Bij ₀ decreases during reaction with sulfur vapors. In the PN transition region there is a significant reduction in the concentration of free carriers (holes), as indicated by the above equation, in the surface area

248 690 kennel Bi ₂ Te ^ _-x S _x with n-type conductivity. The area near the PN junction is likely to be a variable width band structure ·

An apparatus for preparing the BigTeyBigTe structure by diffusion of sulfur gas into the p-type Bi 2 Te 4 is shown in Figure 1. The apparatus consists of a quartz vial (1) in which a sample Bi ₂ Te 4 is placed on a graphite bed (2). (3) and sulfur (4) in the second portion of the vial (1), wherein the temperature in the furnace is measured by thermocouples (5). The ampoule (1) is placed in a ceramic furnace (6), the winding (7) of which consists of two sections allowing adjustment of the desired temperature gradient in the furnace. Furthermore, in a ceramic furnace (6) inserted steel tube (8) 'eliminate local temperature gradients and providing a homogeneous temperature distribution in both parts of the furnace · To eliminate the possibility of sublimation of sulfur on a sample of Bi ₂ Te ^ | is always melting the crystal slightly higher than the temperature of the liquid sulfur. Thus, the apparatus shown in Fig. 1 allows the interaction of BigTe-1 crystals with sulfur vapors, allows the temperature Tp at which the crystal reacts with the sulfur vapors, the temperature of the molten sulfur T _{2 to} control the vapor pressure of the vial in the vial and type Bi ₂ Tě _{> x} S _x .

The preparation of a single crystal structure with the BigTe ^ -BigTe ^ 8 ^ 8-N composition is demonstrated by the following examples:

Example 1

The p-BigTe® crystal (concentration of holes 2.4 x 10 ¹⁸ holes cm 3) in the form of a 60 x 10 x 4 mm moaocrystalline plate is placed in one part of the vial shown in Figure 1, and the other part of the vial is filled with sulfur 5N. The ampoule is evacuated and sealed ·

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After placing the vial in the ceramic furnace, tempering is performed under the following conditions: crystal temperature = 420 ° C, liquid sulfur temperature T ₂ = 230 ° C, sulfur vapor tan 800 Pa, tempering time t «48 hours · After crystal exposure in sulfur vapors relative quench cooling of the crystal by removing the crystal tempering ampoule from the furnace and leaving it at room temperature for several hours. · The obtained crystal is split not in the middle of the shortest side of the sample along the surfaces (0001), have p-BigTe ^ on one side and n-Bi ₂ Te ^ _eX S _x · on the other

Example 2

The same single crystal p-Bi ₂ Te plates as in Example 1 are placed in a quartz ampoule with powdered sulfur, the ampoule space is purged with argon, the vacuum is depleted to 40 Pa and the ampoule is sealed · Pofcmw the ampoule is placed in a sulfur furnace melt at elevated temperature and temper single-crystal platelets in liquid sulfur at 25 ° C for 120 hours. After completion of annealing, the vial is cooled in air to room temperature, the sample areas that have been in contact with sulfur * with grinding and polishing. cleaned of excess sulfur and after splitting along the surface (0001) to obtain the single crystal structure _{BigTech-Bis-2} Te ^ _ _x S _x ·

Figure 2 schematically shows a crystalline diode made of a single crystal Bi ₂ Te ^ -Bi ₂ Te ^ _vX S _x · The BigTe ^ composition side (9) is provided with a gold contact surface (10) formed either by gold paste, or by reduction of gold chloride · On the composition J® ^{n »no} hay e.g. · stříbr248 890 to the trap in the form of spherical droplets (12) where possible, of small dimensions, which makes contact with the feed pile silver or gold wire (13) · the finished structure 8 PN junction based on p-BigTe ^ - n-BigTe ^. ^ Is sensitive to infrared radiation ·

Fig. 3 shows the volt-ampere characteristic, ie the dependence of the passing current on the applied voltage, of the prepared crystal diode.

Fig. 4 shows the spectral distribution of the voltage caused by the interaction of IR radiation with the sample. This voltage dependence on the wavelength of incident radiation was measured at room temperature as follows: sodium chloride) a beam of wavelengths of 2-10 µm; monochromatic light, interrupted at 6.17 Hz, hit the sample and the resulting AC signal was measured using a suitable transformer coupling of a preamplifier and a UNIPAN-type amplifier. During the measurement, the contacts on the sample were shielded to eliminate the contact phenomena · The measurement was repeated after one week within 3 months and was found to be perfectly reproducible and good signal stability ·

It should be pointed out that the above procedure for preparing the PN transition on BigTe ^ crystals is original, has not been described in the literature yet, and undoubtedly is the simplicity, perfect process control and reproducibility of the prepared PN transition crystals. temperature and time of annealing of the crystal sample can be prepared Bi2 ^Ie 3 x ⁸ x ^S ^ ² * ^R '

G 248 890 with a sulfur content in the region of the n-type conductivity and thus it is possible to prepare infrared sensitive crystals in the wavelength range 2-8 µm.

Claims (3)

1 * Method for the preparation of aonocrystalline structures of bisnitium telluride - bisulfite telluride BigTe ^ - ®i> 2 ^T * 3-x ^S x 'where x 0,00 0.001 - 0.4, with variable width of the banned steam caused by the sulfur concentration gradient and simultaneously with PN a transition, characterized in that the single crystals of the p-type BigTe ^ pure or doped are tempered in contact with sulfur at a temperature of 120-500 ° C for 10-400 hours and, after tempering, resolved along the surface (0001) · 2. The method according to claim 1, wherein the contact of the p-type BigTe2 crystals, pure or doped, is carried out in sulfur vapors at a temperature of 150-500 [deg.] C, the pressure of which is 0.080 to 150 kPa, for 10-400. hours · Process according to claim 1, characterized in that the contact of the β-type BigTe ^ crystals, pure or doped, is carried out with liquid sulfur at a temperature of 120-400 ° C for 10-400 hours.