Conductivity compensation and deep traps in epitaxial n-GaAs irradiated by electrons

A study has been made of electrophysical properties and deep traps in epitaxial n-GaAs grown by the chloride method and irradiated by electrons in the temperature range (20–500)°C. It is shown that the natural conductivity of GaAs is attained at irradiation temperatures of 20°C due to the introduction of E traps, and for 300°CT_irr500°C of high-temperature P traps, presumably defect clusters.V. D. Kuznetsov Siberian Physicotechnical Institute at the State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 57–60, October, 1992.     

Electrical properties of GaAs layers irradiated by H4 ions

The quantities(D) and(T) are studied in n- and p-GaAs, irradiated at T = 300°K by H⁺ ions (5 MeV). It is shown that the resistance of lightly doped GaAs specimens increases from original values of ₀ to 10⁹ ·cm upon irradiation by H⁺ ions (5 MeV) to integral fluxes up to D^* – 10¹⁵ H⁺/cm². For D > D^* the layer resistance decreases from 10⁹ ·cm to 1 ·cm at 300°K. It was found that all the GaAs specimens intensely irradiated by H⁺ ions had p-type conductivity near 300°K. Isochronic annealing of radiation defects was studied in the temperature interval 20–700°C.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 39–43, January, 1982.     

Gas formation in liquid in initial stages of a pulsed discharge

Gas formation in electrolytes with=10^–2–10^–4–1cm^–1, distilled water = 10^–5-1.5 ·10^{–6 –1}cm^–1, and chemically pure n-hexane in the initial stages of formation of discharge with rectangular voltage pulses of 0.67 and 1.85 sec duration is investigated. The experimental results are compared with the results of approximate calculations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 42–47, November, 1972.The authors thank V. V. Ryumin for taking part in the discussion of the results and V. V. Lopatin for participation in the experiments with electron-optical light amplifier.     

Scaling functions of susceptibilities toO(1/n) forn-vector models with axial anisotropy

For an axially anisotropicn-vector model withm = O(n) easy – andn – m = O(n) hard components of the order parameter, we derive the susceptibility r ^–1 along one of the equivalent easy axes and the perpendicular one r ^-1 toO(1/n) of the 1/n-expansion in the disordered phase. The results confirm predictions of the scaling theory, e.g.(g, t)=A t ^– X (B g/t ) and (g, t) =A t ^– X (B g/t ), wheret = T – T _c (g = 0),g is the anisotropy parameter andX, X denote the scaling functions. We evaluate the relevant diagrams toO(1/n) which yield the coefficientsA, A and the critical behaviour of the scaling functions and critical amplitudes explicitly for . The extreme anisotropic case, i.e.m = O(1), is discussed briefly in the large-n limit in comparison with the mean field solution.Parts of this paper were presented at the Frühjahrstagung der Deutschen Physikalischen Gesellschaft in Freudenstadt (May 1974).     

Long-wave optical absorption in electron-bombarded GaAs

The absorption spectra of n- and p-type GaAs bombarded with 2-MeV electrons at T=300K were studied in the spectral range from 0.2 eV to Eg. It was found that shallow radiation-defect levels E_c – 0.01 eV and E_c + (0.06–0.1) eV were formed. The structureless character of the absorption in the region h < Eg in electron-bombarded gallium arsenide specimens was shown to be due to the distinctive features of photoionization of deep levels and the strong electron-phonon interaction in this material.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 93–97, July, 1981.     

Decay of the Bethe–Salpeter Kernel and Bound States for Lattice Classical Ferromagnetic Spin Systems at High Temperature

We consider lattice classical ferromagnetic spin systems at high temperature (1) with nearest neighbor interactions and even single-spin distributions (ssd). Associated with each system is an imaginary time lattice quantum field theory. It is known that there is a particle of mass m–ln in the energy-momentum spectrum. If s ⁴–3s ²²<0, where s ^k is the kth moment of the ssd, and is sufficiently small, we show that in the two-particle subspace there is no mass spectrum up to 2m. For >0 we show that the only mass spectrum in (m, 2m) is a bound state of mass m _b=2m+ln(1–)+O(), where =(+2s ²²)^–1. A bound on the decay of the kernel of a Bethe–Salpeter equation is obtained and used to prove these results.     

Effective Stimulated Emission Cross-Sections of Poly(Phenylene Vinylene) Copolymers in Toluene Solution

We report optical gain measurements in four different copolymers polyp-phenylene-co-[2,5-dioctyloxy-p-phenylene-bis-2(4-nonyl phenyl) vinylene]nonyl-PpPV, polym-phenylene-co-[2,5-dioctyloxy-p-phenylene-bis-2(4-methyl phenyl) vinylene]methyl-PmPV, polyp-phenylene-co-[2,5-dioctyloxy-p-phenylene-bis-2(4-methyl-phenyl) vinylene]methyl-PpPV, polyp-phenylene-co-[2,6-naphthylene-bis-2(4-nonyl phenyl) vinylene]nonyl-PpPV-NV in toluene. The copolymers are related to poly(phenylene vinylene) and have been synthesized via Horner–Emmons polycondensation reaction. The optical gain determined from the amplified spontaneous emission (ASE) intensity is dependent on the excited stripe length. The net optical gain coefficients are found to vary between 0.1 cm^–1 in nonyl-PpPV to 2.5 cm^–1 in methyl-PmPV under nanosecond pulse excitation. The gain for Rodamine 6G was also measured under the same experimental condition and was used to determine the stimulated emission cross-sections for the four polymers and found to be _SE(peak)= 6.7 × 10^–20 cm² for nonyl-PpPV, _SE(peak)= 1.7 × 10¹⁸ cm² for methyl-PmPV, _SE(peak)= 1.4 × 10^–18 cm² for methyl-PpPV, and _SE(peak)= 1.5 × 10^–18 cm² for nonyl-PpPV-NV.     

On the indistinguishability of classical particles

If no property of a system of many particles discriminates among the particles, they are said to be indistinguishable. This indistinguishability is equivalent to the requirement that the many-particle distribution function and all of the dynamic functions for the system be symmetric. The indistinguishability defined in terms of the discrete symmetry of many-particle functions cannot change in the continuous classical statistical limit in which the number density n and the reciprocal temperature become small. Thus, microscopic particles like electrons must remain indistinguishable in the classical statistical limit although their behavior can be calculated as if they move following the classical laws of motion. In the classical mechanical limit in which quantum cells of volume (2)³ are reduced to points in the phase space, the partition functionTr{exp(–) for N identical bosons (fermions) approaches (2)^–3N(N!) ... d³r₁ d³p₁ ... d³r_N d³p_N exp(–H). The two factors, (2)^–3N and (N!)^–1, which are often added in anad hoc manner in many books on statistical mechanics, are thus derived from the first principles. The criterion of the classical statistical approximation is that the thermal de Broglie wavelength be much shorter than the interparticle distance irrespective of any translation-invariant interparticle interaction. A new derivation of the Maxwell velocity distribution from Boltzmann's principle is given with the assumption of indistinguishable classical particles.     

Investigation of β–ν Angular Correlation in the β+ Decay of 18Ne and 14O

The – angular correlation in the ⁺ decay of ¹⁸Ne and ¹⁴O has been investigated using a new experimental technique. The technique is based on the precise measurement of the energy Doppler shift of a -quantum following the ^± decay. The measurement with the ¹⁸Ne isotope gives the – angular correlation coefficient = +1.06 ±0.19 which corresponds to a constraint on the scalar interaction of {|C_S|²+|C'_S|²} 0.29|C _V|. An inter-atomic interaction between the ¹⁴O daughter atom (¹⁴N) and a CO complex has been studied in a measurement with the ¹⁴O isotope.     

The “Del'fin” high-power laser facility for heating spherical thermonuclear targets

The Del'fin H twelve-channel laser facility for high-temperature heating of thermonuclear targets in a spherical geometry is described. It consists of a neodymium driver laser with maximum energy ~10 kJ, pulse duration 10^-10–10^-9 sec, andbeam divergence ~5·10^–4 rad, a vacuum chamber in which the laser radiation interacts with the plasma, and the devices for the diagnostics of the laser and plasma parameters. The Del'fin focusing system, which ensures a high degree of symmetry of the spherical irradiation of the target at a maximum flux density on its surface ~10¹⁵ W/cm², is described. The problem of realizing the maximum ability of heating spherical thermonuclear targets by radiation from high-power laser systems is considered.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P.N. Lebedeva, Vol. 103, pp. 3–51, 1978.     

Wetting transition on grain boundaries in Al contacting with a Sn-rich melt

The contact angle at the intersection of a grain boundary in Al bicrystals with the solid Al/liquid Al–Sn interphase boundary has been measured for two symmetric tilt <011> {001} grain boundaries with tilt angles of 32° and 38.5°. The temperature dependencies (T) present the evidence of the grain boundary wetting phase transition at T_w. The observed hysteresis is consistent with the assumption that the wetting transition is of first order. The determined discontinuity in the temperature derivative of the grain boundary energy is–5.6 J/m²K (T w1=617°C) for the boundary with a low energy (=38.5°) and –17 J/m²K (T w2=604°C) for the grain boundary with a high energy (=32°).     

The effect of low-temperature electron irradiation on the transition temperature of YBa2Cu3O7−δ superconductors

Measurements of the complex susceptibility =–i of electron-irradiated YBa₂Cu₃O_7– show a strong influence of the electron irradiation dose, ·t on the transition temperatureT _c . For irradiation doses of ·t=2.2·10¹⁹ e^–/cm² we find a damage rate of T _c /(·t)=–1.6·10^–19 K/(e^–/cm²). It is assumed that the decrease ofT _c is mainly a bulk effect due to the production of atomic defects like vacancies and interstitials in the Cu–O–Cu chains and in the basal planes of the unit cells.     

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.     

Humidity dependence of the atmospheric absorption coefficient in the transparency windows centered at 0.88 and 0.73 MM

A dependence is investigated of the absorption coefficient of atmospheric water vapor on absolute air humidity in the spectral intervals =11.1+12.0 and 13.2+14.3 cm^–1 by a radiospectrometer with a multipass vacuum cell. Measurements are carried out in the humidity range 3+23 g/m³ at 140 m length of the optical path.Parts of the absorption coefficient linearly and quadratically depending on have been separately defined from the experimental data. In particular, it has been obtained for the centers of transparency windows: (=0.73mm) [dB/km]=1.68 (±0.08) +0.019 (±0.004) ², (=0.88 mm) [dB/km]=0.83 (±0.06) +0.013 (±0.002) ². The given values correspond to the temperature of 306 K and the pressure of dry air of 735 Torr.A comparison is made between our results and theoretical calculations and data of other measurements.     

The Action of √−Δ on Weighted Sobolev Spaces

The action of – on distributions is examined within the context of weighted Sobolev spaces. The results obtained are as follows: (1) – is a continuous map of R ⁿ ), the space of rapidly decreasing functions, to L ^{2, s} (R ⁿ for any s < n/2 +1; (2) if k R and s > –n/2 – 1, then – is a continuous map from H ^{k, s} (R ⁿ ), the weighted Sobolev space, to H ^{k–1, t} (R ⁿ for some t. The results are optimal in a sense.     

How to measure the magnetic moment of the tau lepton

We present a method for obtaining bounds on the magnetic moment of the lepton. In order to do this, we study the radiative decayW as a function of the anomalous magnetic moment of the ,a . One can obtain bounds as good asa < 4.05×10^–2, 2.25×10^–2, 4.5×10^–3, and 2.5×10^–3 at the present Fermilab, future Fermilab, SSC, and LHC, respectively.     

Photoelectric characteristics of materials Pb1-xSnxTe?In? subject to microwave and infrared emission

Current/voltage (CV) characteristics of solid solutions Pb_1–xSn_xTeln (with D. 22x3. 24 and 0.2N_In1.0 atomic percent) were studied at He temperatures, in presence of background at 300K. Also the photoconductivity of these materials was measured in conditions of background screening and illumination at wavelengths 100µm and 2mm.CV-characteristics are interpreted within a model of two-electron capturing by Jahn-Teller centers. Photoconductivity in millimeter and submillimeter wavebands, having relaxation times less than 10^–5 sec, is related with heating of electronic gas in process of electromagnetic power absorption by the free carriers.     

Defect study on electron irradiated GaAs by means of positron annihilation

Measurements of the positron lifetime and Doppler-broadened annihilation-radiation have been performed in electron-irradiated GaAs. The positron lifetime at the irradiation induced defects was 0.250 ns at 300 K. The defect clustering stage was found to occur at around 520–620 K, and the coarsening and annealing stage is believed to be above 620 K. Similar annealing stages were also observed in GaAs lightly doped with Si (0.2×10¹⁸ cm^–3). Both the lifetime and the S-parameter in the irradiated GaAs were found to decrease with temperature from 300 K to 100 K, suggesting the coexistence of shallow traps in electron irradiated GaAs.     

The PSI experiments on muon-catalyzed pt fusion

The experiments on pt fusion performed at Paul Scherrer Institut, Villigen, Switzerland, are described. Liquid triple mixtures of protium, deuterium and tritium with low concentrations on deuterium and tritium were used. Gamma rays, X-rays, neutrons and, for the first time, conversion muons, were measured. Preliminary results are: Rate for spin flip from the triplet to the singlet state of t(1s), ₁₀=(1.0±0.2) × 10³s^–1; rate for muon-catalyzed pt fusion from the (I=1) nuclear-spin state, _pt ^f (I=1)=0.07±0.01s^–1; and the molecular formation rate, _pt ^m =(7.5±1.3)s^–1 (all normalized to liquid hydrogen density).     

Experimental Test of a Time-Temperature Formulation of the Uncertainty Principle Via Nanoparticle Fluorescence

No Heading The uncertainty in the measured fluorescence decay lifetimes of 30 nm particles of YAG:Cc was used to evaluate the predictions of a novel form of the Heisenberg uncertainty principle suggested by de Sabbata and Sivaram, T t h/k. The worst-case uncertainty in temperature of 4.5 °K (as derived from the relationship between temperature and lifetime) and the measured uncertainty in decay lifetime, 0.45 ns, yielded an internal estimate of T t = 2.0 × 10^–9 °K s, which is 263 times larger than /k = 7.6 × 10^–12 °K s. An external estimate of T t = 4.5 × 10¹¹ °K s (which is = 6 times /k) is derived from the independently measured uncertainty in the temperature of the sample and the experimentally determined uncertainty in lifetime. These results could be low by a factor of 5.6 if signal averaging must be taken into account. If valid, the findings are consistent with the predictions of this version of the uncertainty principle and they imply the existence of a type of thermal quantum limit.