Diffusion of cobalt in indium antimonide

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2, No. 11

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OF PAPERS IN SOVIET PHYSICS-SOLID

the incident energy. Monochromatic illumination in the 250-140 mu range was obtained from a vacuum monochromator using lithium fluoride optics and a built-in hydrogen arc lamp. The results

are as follows:

(1) The quantum yield of selenium layers increases gradually at short wavelengths, reaches unity at about 200 rng, begins to exceed unity for higher photon energies, and at about 140 rnp (9 eV) approaches the value 2. Since the energy gap of amorphous selenium is about 2.3 eV, the photon energy which produces the above-mentioned carrier multiplication is about 4 times larger than the energy gap. It also agrees with the the theoretical prediction of carrier multiplication by impact ionization when high-energy photons are absorbed. (2) The selenium-tellurium layers, also aresenic triselenide films, give a much greater quantum yield at long wavelengths than selenium films. (3) The quantum yield of antimony trisulfide does not exceed 0.1 over the whole spectral range. Layers of partially crystallized selenium give a quantum yield of the same magnitude. (4) The quantum yield of the tin oxide layers starts to increase rapidly as soon as the photon energy is sufficient to create hole -electron pairs, and it remains equal to unity until almost 220 rnp. Further increase in wavelength decreases the quantum yield due to the nonphotoactive absorption of radiation inside the film. (5) When the tin oxide was sensitized with organic dyes (tripaflavine, fluores’ceine, and eritrozine) sensitivity appeared in the absorption band of the dye. Then, the magnitude of the quantum yield, in the sensitive region reaches a value near unity, which indicated a very effective sensitization. Bibliography:

17 titles.

CYCLOTRON RESONANCE OF HOT ELECTRONS IN GERMANIUM. F. I. Bakun and E. M. Gershenzon (Vol. 6. No. 9. pp. 2847-2849). The cyclotron resonance of hot electrons in p-type Ge at 9.1 kMc at 4.2OK has been studied. A sufficiently wide microwave power range permitted the observation of the dependence of the

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cyclotron resonance spectra with n = 0.4 at 4.2oK. Samples made of pure p-Ge with an impurity concentration (N + ND < 1013 cm-3, NA - ND - 7.1012 cm- 9 , have been used for this experiment. The following considerations were used in selecting the samples: (a) the purest single crystals of Ge contain acceptor impurities, (b) observations of the heating of electrons in the wide microwave power range is conveniently conducted, namely in the p-Ge, since the impact ionization of the non-compensated impurity centers (in the present case, acceptors) heated up by carriers in the electric field does not affect the concentration of electrons, and consequently does not distort the lines of the cyclotron resonance of the hot electrons. p-Ge samples, cut in the form of discs 2 mm dia. and 0.15 mm thick, in a (110) plane, were attached to the ends of jigs made from organic glass, in light-conducting holders made of thin-walled tubing, and were introduced at the antinode of the electric field of a rectangular TEiO2 resonator pump through an opening in the end wall. The Q of the resonator with the sample at 4.2oK was not less than 5.103. As a result of the experiment it has been established that, of the four minima of the conduction zone, when the electrons belong to the one which is located on the (111) axis close to the direction of the magnetic field H, mE* is at a minimum and is independent of the orientation of the magnetic field in the plane perpendicular to H. In the case of the electrons in the remaining three minima, mE* is essentially determined by the orientation of the electric field. These results are used to explain the dependence of the line width ( aTp)-l for the electron cyclotron resonance as a function of microwave power incident the cavity for a number of samples. Diagrams of the cyclotron resonance spectra ,of carriers doe several values of microwave power are discussed. It is noted that the spectral lines of the electron cyclotron resonance are wide enough, even for the purest materials, so that the widening due to electron quickly leads to an overlap of the spectral lines. The magnitude of the effect is determined by the.amplitude of the microwave electric field in the sample, and therefore depends on the Q of the resonator used and the method of positioning the sample. It is assumed that the variation in the microwave power is due to the fact that the range of the frequencies used in the experiment allows working with high Q cavities. Bibliography: 6 titles. DIFFUSION OF COBALT IN INDIUM ANTIMONIDE. I.A. Gusev and A. N. Murin (Vol. 6,

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9, p. 2859).

The diffusion of radioactive cobalt, Co60, in n-type indium antimonide was studied in the temperature range 425-5000C. Samples, from a single crystal, were cut perpendicular to the (111) direction of the form of plane-parallel plates having the dimensions 0.8 x 1.2 x 0.25 cm, and having the following parameters at 77oK: ; = 0.03 ohm-cm, n = 1015 cm-3, u= 3.105 cm2 per sec. The dislocation density is 6.5.103 cmm2. The radioactive cobalt was deposited electrolytically on the sample surface from a solution containing CoC12 and disulfate nephthalic acid [ClO~8@03)2]. The sample surfaces were etched with CP-4A etching agent. The experiment was conducted by the method described in the paper by I. A. Gusev and A. N. Murin [FFT 6, 1208 -(1964)]. Samples were annealed for at least 24 hr. It has been established, on the basis of X-ray structure analysis, that InSb-Co phases do not form on the surfaces of the samples during the diffusion process. The annealed samples were etched with hot 50 per cent HCI, and then a layer -100 p was removed from their side facets. Diffusion was studied by the layer method. It is confirmed that diffusion takes place from a constant source. The temperature dependence of the diffusion coefficient may be described by the expression D = 2.7 - lo-l1

0.39 exp(-r)

cm2/sec

The solubility of cobalt in InSb is -2. 1OIg at the indicated temperature range. Bibliography:

1 title.

SPIKED CONDUCTION AND PHOTODIELECTRIC’EFFECT IN GERMANIUM. V. P. Dobrego, J. Oksman, S. M. Ryvkin and V. N. Smirnov (Vol. 6, No. 9, pp. 2860-2862). An investigation of peculiarities of the photodielectric effect has been conducted under the conditions when the electric conductivity is determined by the spiked mechanism, i.e. in the present case, at helium temperatures: at nitrogen temperature the antimony levels are ionized and the observed phenomena must be described as photoconductivity of the double layer semiconductor in alternating current, or as the photodielectric effect of the second type. The measurements were cinducted by the method described by J. Oksman et al. [FFT 5, 2885 (1963)]. The measured current,suppned to the

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Vol.

2, No. 11

photodielectric capacitor (germanium crystal spaced from the electrodes by dielectric spacers) did not exceed 0.5 V (1 V/cm) in order to avoid an impurity breakthrough. All experimental results are tabulated. Measurements of the bulk and active conduction at nitrogen temperature correspond to the laws peculiar to photodielectric effect of the second type. At 4.2oK the bulk conduction increment in both samples is different from zero and cannot be described by means of photodielectric effect of the second type. The relaxation time of the photodielectric effect at nitrogen temperature is measured in millisec. while the drop of both components of conductivity at 4.2oK is sharply nonexponential and lasts many minutes. With an increase in intensity of excitation, both conduction components, measured at 4.2oK, rise sublinearly, and with larger frequency there is larger conduction. An assumption is made that the transfer carriers at 4.2oK in the samples is accomplished by jumps of the carriers along the antimony levels. A mechanism of the spiked conductivity is discussed. It is noted that this mechanism, as such, does not necessarily lead to the change in polarizability, i. e. to the photodielectric effect of the first type. The latter must be observed in those cases where the number of the short chains is large in comparison with the number of long chains, i.e. at . not very high concentrations of the main impurity. It is supposed that this was the case in the investigated samples. It is noted that the possibility of observing the photodielectric effect of the first type, identified by the spiked conductivity, depends on the size of the impurity centers, degree of compensation, and temperature; in the authors’ view similar effects may also take place for deep impurities, which is evidenced by the “freezing” of the photodielectric changes, brought about by illumination in the zinc sulfide phosphors. A deduction is made, on the basis of the experimental results, that the photodielectric effect of the first type really exists in the compensated germanium crystals at helium temperature and is evidenced by jumps of the non-equilibrium carriers along the impurity levels. Bibliography:

6 titles.

PARAMAGNETIC RESONANCE ABSORPTION IN Gd-Ce. I. Pop and V. I. Chechernikov (Vol. 6, No. 9, pp. 2876-2877). Resonance absorption in Gd-Ce has been investigated for the following sitions: 65, 73.8, 80, and 95 per cent Gd. The experiment was conducted in

alloys compoby weight the 3 cm