The effect of adsorbed impurities on the surface properties of GaAs and the characteristics of electroluminescent p-n junctions

The effect of adsorbed copper and gold on the band bending, the steady-state photoconductivity, and the field-effect mobility in n-type GaA s has been studied. The light and electrical characteristics of electroluminescent p-n junctions have also been studied. It is shown that doping the GaA s surface with Cu and Au leads to an increase of the depleting band bending and to a decrease in the field-effect mobility. Copper, adsorbed at the surface of slices before diffusion, leads to a reduction of the radiative intensity of the p-junctions prepared on GaA s with an electron concentration of 1–6·10¹⁷ cm^–3, to a decrease in the cutoff voltage, and to an increase in the differential resistance of the forward branch of the volt-ampere characteristics. It is proposed that in the region of the experimental current (5·10^–2-10^–2) mA the presence of Cu in the electroluminescent p-n junctions leads not to a change in the injection mechanism but to an increase in the series resistance of the p-n junction.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 72–77, December, 1973.     

Characteristic diffusion constants of cadmium in silicon

This investigation was devoted to experimental determination and analysis of curves describing the diffusive distribution of cadmium in silicon at different levels of prealloying of the silicon with phosphorus and different temperatures of isothermal diffusion, with allowance for the characteristic exponential relation between the pre-exponent D₀ and the activation energy Q. Numerical values of D_k and Q₀ were found. They are equal to 4·10^–8 cm² · sec^–1 and 0.22 eV, respectively.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 65–68, November, 1984.     

Diffusion coefficient of selenium in indium antimonide

The diffusion of selenium in indium antimonide has been studied in the temperature range 400–490°C, by the method of removing layers. Two regions have been distinguished in the donor distribution profiles. The first has a low diffusion coefficient and a high surface concentration, near to the limit of solubility of selenium (8·10¹⁸ cm^–3). In the second region, a much larger diffusion coefficient and a surface concentration lower by two orders of magnitude (8·10¹⁶ cm^–3) with weak temperature dependence are found. The temperature dependences of the diffusion coefficients of the first and second regions can be described by the expressions: D=4.8·10¹³ exp(–4.1 eV/kT) cm²/sec, D₂=1.9·10¹³ exp(–3.9 eV/kT) cm²/sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 40–43, November, 1991.     

The effect of an anisotropic pressure on the reverse currents and the lifetime of minority carriers in germanium diodes

The effect of pressure on the reverse currents, the lifetime of minority carriers and the charging capacitance of fused germanium diodes is considered. The p-n junctions are arranged in the (111) crystallographic plane. It is established that the reverse current increases rapidly with increased pressure. The lifetime of minority carriers falls by a factor of 1.5 to 2 up to a pressure of 3 · 10⁹ dyne/cm² and the charging capacitance increases. Starting from a pressure of 3 · · 10⁹ dyne/cm² the lifetime of minority carriers increases and the charging capacitance is reduced to a particular constant value. A qualitative explanation of the dependence of _e, Cj and I_rev is given.     

Correlation betweenJ c and screw dislocation density in sputtered YBa2Cu3O7-δ films

Electric transport properties of sputtered YBa₂Cu₃O_7– films were studied as a function of screw dislocation density, ranging from 5·10⁷ cm^–2 to 1.3·10⁹ cm^–2 as determined at the film surface. A correlation was found between the number of screw dislocations and the critical current density (J _c ). Films with higher screw dislocation densities have higher critical current densities and a slower drop ofJ _c as a function of applied magnetic fieldH.     

Electrical properties of Al-SiO2Si structure with plasmochemical insulator: Potential barrier heights and electron capture in SiO2

It is shown that in the forbidden band of the plasmochemical SiO₂ there are electron capture centers with capture cross section 2·10^–13cm², density 2·10¹⁹ cm^–3, and thermal activation energy 0.41 eV for the process of trap emptying. It is noted that the charge state of the insulator in an external electric field is unstable, this being due to the exchange of electrons between the insulator and the aluminum electrode. An energy band diagram of the structure is deduced from the results of the investigation. The potential barrier heights were found to be 2.78 eV at the Al-SiO₂ interface and 4.36 eV at the SiO₂-Si interface. The dynamical current-voltage characteristic of the structure is used to determine the density of mobile ions in the insulator, which is found to be S·10¹³ cm^–2 at T=230°C and rate of change 5 mV/sec of the voltage.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 61–66, January, 1981.     

Spectral Properties of Single Crystals of Synthetic Diamond

The half-width of the spectrum of Raman scattering (RS) of the first order of a diamond single crystal grown in a nickel-free system containing nitrogen getters is identical to all growth sectors (1.69 ± 0.02 cm^–1). The sectorial inhomogeneity is not reflected in the transmission spectra and birefringence of this crystal. The nitrogen concentration is 4·10¹⁷ cm^–3. For different growth sectors of the diamond crystal grown in the Ni–Fe–C system, the half-width of the Raman line varies from 1.74 to 2.08 cm^–1, differences in the transmission spectra and birefringence are observed, and photoluminescence is revealed. The concentration of nitrogen in the growth sectors {001} is 1.6·10¹⁹ cm^–3, the content of nickel is estimated to be at a level of 10¹⁹ cm^–3, and the content of nitrogen in the {¯111} sectors is 4·10¹⁹ cm^–3.     

Electroluminescence at p-n junctions in ZnSe

Electroluminescent radiation at p-n junctions and the photovoltaic effect in ZnSe monocrystals were investigated. The p-n junctions were prepared by melting dots of indium on p-type ZnSe (ZnSe contained Cu impurities).The measurements were made at room temperature and at –150°C. The acceptor level depths estimated from a maximum emission are in accordance with the data in the literature.The decay time of electroluminescence measured at –150°C is 2·1×10^–6 sec. In sunlight a photovoltage of about 1·1 V was observed.I wish to thank Prof. Dr A. Jablonski for his interest in this problem.     

Determination of the strain potential constant by means of the p-InSb photoconductivity spectra under uniaxial compression

The influence of uniaxial pressure (0 < P < 2600 kg/cm2) on the intrinsic photoconductivity (PC) spectrum of p-InSb at 93 and 15°K is investigated. At 77°K the carrier concentration and mobility in the specimens were, respectively, (1.4–3.2)·10¹⁴ cm^–3 and 7000 cm²/V. sec. It is established that the maximum in the PC(E_m) spectra under compression is shifted towards higher energies. In the low-compression range E_m/P=5·10^–6eV·cm²/kg, while E_m/P=1·10^–6eV·cm²/kg for P > 1000 kg/cm². It is shown that the shift of the maximum of the intrinsic PC spectra with pressure is due to the growC;th in the forbidden bandwidth (E_g), and the change in parameters characterizing carrier diffusion in the specimen bulk (the diffusion coefficient, lifetime, surface recombination velocity) plays no part. The change in E_m/P with pressure is explained by the influence of valence band splitting. The deformation potential constants of the valence band |b|=(1.7±0.3) eV and |d|=(4.4±0.8)eV are calculated on the basis of a comparison between experimentally obtained data and theoretical results.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 159–162, February, 1976.     

Interaction of triplet excitons with excited naphthalene and deuteronaphthalene molecules in benzophenone crystals

An increase in the intensity of the exciting light is shown to cause a significant decrease in the quantum yield and rise time of the sensitized phosphorescence of impurity C₁₀H₈ and C₁₀D₈ in benzophenone crystals. Nonlinear quenching of the impurity phosphorescence occurs because one or two excitations are quenched in the interaction of triplet excitons with impurity molecules in the excited state in which they are left after the first exciton capture. Experiments show the nature of the changes in the quantum yield and the rise time of the impurity phosphorescence as the exciting-light intensity is varied from 3.6 · 10¹² to 6 · 10¹⁶ photons/cm² · sec depends strongly on the impurity concentration, the crystal thickness, and the lifetime of the triplet state of the impurity molecules. The experimental results are in good agreement with a proposed theory for the kinetics of the interaction of triplet excitons with impurity molecules in the ground and triplet states.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 8, pp. 12–16, August, 1969.     

An optical bridge reflectometer for sensitive measurement of ion implantation dose

An instrument is described that can be used to monitor, with unprecedented sensitivity, changes in the optical reflectivity due to crystailine damage incurred during ion implantation. It is shown that at the shot-noise limit, changes in the optical reflectivity of silicon as small as 5·10^–7 can be measured in a 10 Hz bandwidth with a signal-to-noise ratio of 100, corresponding to an extrapolated uniform implantation dose of 5·10⁸ cm^–2 for ¹¹B⁺ at 50 keV in silicon.     

The behavior of copper impurity in CdSnAs2

Single crystals of n-type CdSnAs₂ with a carrier concentration of 2 ·10¹⁷–4 ·10¹⁸ cm^–3 and mobility (3 to 6) · 10³ cm²/V ·sec were copper doped by diffusion saturation at temperatures from 400 to 570C. As a result of the study of the electrical properties of the doped crystals it was established that the copper in CdSnAs₂ is a fast-diffusing acceptor impurity. The solubility of Cu depends primarily on the donor-center concentration and has clearly a retrograde character. Low-temperature heat treatment (over the 200–400C range) of the Cu-doped specimens results in an increase in the acceptor concentration. The form of the log R(10³/T) curve indicates the existence of acceptor centers with an ionization energy of 0.05 eV in the Cu-doped CdSnAs₂ specimens.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 7, pp. 39–44, July, 1973.     

Nuclear spin lattice relaxation of191mIr in Fe

Thermal cycling of the lattice temperature was used to determine the nuclear spin lattice relaxation of^191m IrFe in polarizing fields of 0.05 to 1.3 T. At low temperatures, the relaxation time is not very much shorter than the lifetime of^191m Ir. In the first part of the paper, the master equation formalism is extended to include a finite lifetime. Our result for the reduced relaxation constant, ² C _K =(1.48±0.11)·10¹⁴ K s^–1 T^–2 (high field limit) is in serious disagreement with that of a spin echo measurement of¹⁹³IrFe, but fits much better into the general systematics. A comparison of relaxation rates for 3d-, 4d-, and 5d-impurities in Fe is given. As a by-product, a Kapitza conductivity constant ofl _K =1.5 mW cm^–2 K^–4±30% was found between Fe and dilute³He/⁴He.     

Properties of MOS-structures based on anode-oxidized CdSnAs2

The properties of metal (Al, Au)-anodic oxide-CdSnAs₂ monocrystal structures are studied. It is established that MOS-structures using undoped CdSnAs₂ crystals show a high positive fixed charge in the anodic oxide (N_S 5·10¹² cm^–2) and high surface state density on the oxide-CdSnAs₂ boundary surface (N_SS 2·10¹³ cm^–2·eV^–1). In MOS-structures using diffusion-doped (copper) crystals the sign of the fixed charge is negative (N_S 10¹¹ cm^–2, N_SS 2·10¹² cm^–2·eV^–1). The latter structures show a definite photosensitivity and photomemory. The possibility of effective control of the fixed charge value within the oxide by illumination is shown. The surface state distribution over energy, time constant, and capture section is determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 90–93, September, 1982.     

Photocurrents in p-n Si diodes under high intensity (pulsed-laser) illumination: Quantum yields and kinetic evaluation

The photoelectric response of p-n Si photodiodes under pulsed laser illumination (half width 10 ns) at 532 nm was studied as a function of dose which was varied over 6 orders of magnitude. The photocurrent transients are dominated by a plateau-like feature due to the build up of space charge at the intensities used. Increasing bias voltage increases the height of the plateau and decreases its length. In the low-dose range the length of the transient increases linearly with dose and the collected charge (integrated current) reaches a constant value. At high doses (above 10^–5 J/pulse · cm² or 2.7×10¹³ quanta/pulse · cm²) considerable charge loss (decrease in quantum yields) is accompanied by a less than proportional increase of the transient lifetime. From model calculations the dose and voltage dependence of the quantum yield of charge collection is shown to be the result of competition between current flow and first and higher order recombination. The model calculations are consistent with experimental results. Rate constants have been obtained by fitting.     

Effect of the defectiveness of a semiconductor on the characteristics of Pd-GaAs contacts

A study was made of the volt-ampere characteristics of Pd-GaAs Schottky barriers in relation to the defectiveness of the gallium arsenide. The defect content of the material was checked metallographically and by the method of x-ray topography. Single crystals of GaAs doped with Ge, Ge + Sb, and Ge + In were studied. Here, the electron concentration was (1–4) · 10¹⁵ cm^–3, and mean dislocation density ranged from 4·10⁴ to 2·10² cm^–2. The defectiveness of the material was altered by the introduction of different concentrations of isovalent impurities. It was shown that for diodes produced by the same technology, the manifestation of low-temperature VAC anomalies and the current mechanism are determined by structural features of the semiconductor (by dislocations and microdefects).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 90–95, July, 1988.     

Effect of vibrational kinetics of He2 + ions on the afterglow of a discharge in helium

A decaying weakly ionized helium plasma [n_e=(0.2–1.1)·10¹¹ cm^–3, p=(40–70) mm Hg] was studied experimentally. It is shown that the experimental time dependences of the intensities of atomic lines and molecular bands in the afterglow phase can be explained if the vibrational kinetics of He₂ ⁺ ions is included in the analysis. Analysis of the measurements shows that for n_e 10¹¹ cm^–3 and N_a 10¹⁸ cm^–3 deexcitation of He₂ ⁺ ions occurs primarily as a result of inelastic collisions with helium atoms. Based on the experimental data, an approximate value was obtained for the rate constants of the vibrational relaxation of molecular helium ions 10^–16 cm³/sec. These results are used for making a qualitative analysis of the distribution of He₂ ⁺ ions over the vibrational states in the discharge phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 88–96, November, 1986.     

Electrical properties of p-type ZnGeP2 irradiated by H+ ions

The properties of p-type ZnGeP₂ [p₀=(5–10)·10¹⁰ cm^–3, ₀=(2–5)·10^–7 (·cm)^–1], irradiated with H⁺ ions [E=5 MeV, T_irr=300 K, D=(1·10¹²–1.7·10¹⁶) cm^–2] are studied. An increase in the resistivity (to gr_max - 5·10¹¹ ·cm) and subsequent reduction in for large currents of H⁺ ions ( - 9·10⁸ ·cm for D - 1.7·10¹⁶ cm^–2), is observed in irradiated crystals. The resistivity of irradiated p-type ZnGeP₂ is found to be very sensitive to hydrostatic pressure [(4–5)·10^–5 bar^–1]. The annealing of radiation defects in the temperature interval (20–600) °C is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 91–93, October, 1991.     

Effect of electron irradiation on the properties of germanium-doped gallium arsenide

The Hall effect, electrical conductivity (77–370 K), and photoluminescence spectra (77 K) are studied in single-crystals of nuclearly doped GaAs (NDG) and GaAs doped with Ge by the metallurgical method after irradiation by electrons (E= 1 MeV, D=1.1·10¹⁵–3.8·10¹⁸ cm^–2). Initial electron concentrations were n= 1.7·10¹⁷ cm^–3 and n₀=2.6·10¹⁷ cm^–3 respectively. In the GaAs doped during crystal growth by the Czochralski method the degree of compensation related to the amphoteric impurity Ge is higher (K=0.8) than in the NDG (K=0.4) for identical initial electron concentration. It was established that the rate of charge carrier removal in GaAs is lower than in NDG, while radiation defects are more thermostable in NDG. The energy spectrum of radiation defects and radiating recombination centers, and the basic steps in reestablishment of electrophysical and optical properties in GaAs and NDG are similar, i.e., they do not depend on the method of germanium doping.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 82–86, April, 1991.     

A study of electronic states near the interface in ferroelectric-semiconductor heterojunction prepared by rf sputtering of PbTiO3

Interface states in the ferroelectric-semiconductor junction have been investigated from analyses of DLTS andC-V data. Two trap levels are located at 0.21 and 0.36 eV below the conduction band near the silicon side of the interface in the MFS (Metal-Ferroelectric-Semiconductor) structure. The interface states density has been drastically reduced by putting an oxide layer between ferroelectric and semiconductor with certain heat treatment in H₂ atmosphere at 500 °C. It has been found that the MFMOS (Metal-Ferroelectric-Metal-Oxide-Semiconductor) structure shows the least interface states density (less than 10¹¹cm^–2eV^–1) with the maximal dielectric constant of PbTiO₃ thin films.