Linear parameters of helical instability in thick silicon wafers at 300 K

An analysis is performed on the dependence of the threshold electric field intensity (E_t) of helical instability of a semiconductor plasma on the magnetic induction and threshold frequency on E_t at a temperature of 300 K allowing for the form of the volt-ampere characteristic curve of the specimen. It is shown that when the field dependence of the charge carrier concentration in the specimen is taken into account, the variation in the rate of surface recombination and volume lifetime in the process of preparing the specimen, the variation in the path of the threshold curve, and the variation in the field dependence of the threshold frequency are satisfactorily described by helical instability theory for the case of a homogeneous plasma for n p and _{n p}. The basic cause of incomplete matching of the experimental and theoretical curves is apparently due to not fulfilling the condition on homogeneity of the plasma and the electric field in the presence of the injection of charge carriers from the contacts.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 49–53, August, 1991.The author is grateful to Yu. V. Medvedev for performing the measurements of the parameters by microwave techniques and to O. N. Merkulova for her assistance in writing the computer program.     

Kink instability of the semiconductor plasma in silicon parallelepipeds

Experimental results on the onset of the kink instability of the semiconductor plasma in silicon p⁺-p-n⁺ structures are analyzed. The structures were parallelepipeds. The experiments were carried out over the temperature range from 77 to 300 K. The shape of the current-voltage characteristics and that of the threshold curves of the test samples are discussed. The frequency and amplitude of the alternating current which arises as a result of the kink instability are described as a function of the electric field and the magnetic induction at levels substantially above the excitation threshold.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Scientific-Research Institute of Semiconductor Devices. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 103–110, May, 1992.     

Annihilation of unthermalized positrons in a silicon single crystal at 77°K

A model is considered for the annihilation of nonrelativistic positrons from quantized states in lattice channels. Annihilation gamma rays of energy over 511 keV have been observed when the positrons from an Na²² source strike a silicon single crystal at 77°K. The experimental results agree well with the proposed model.     

Sulphur-doped silicon background-limited infrared photodetectors near 77 K

The photoconductive properties of sulphur-doped extrinsic silicon infrared detectors prepared by closed-tube diffusion techniques have been investigated. Spectral response data show that this material would be suitable for thermal imaging of 3–5 μm radiation, whilst detectivity measurements as a function of temperature indicate that background-limited operation is achievable near liquid nitrogen temperature (77 K).     

Intervalley transfers of hot electrons in silicon below 77 K

Intervalley rate transfer along 〈100〉 directions is deduced from conductivity measurements versus electric field for different impurity concentrations N_D-N_A at lattice temperatures T ? 77 K. The maximum rate transfer plotted versus T reaches 1 at T < 25 K and does not depend on N_D-N_D for N_D-N_A ? 2 × 10¹⁴crmcm^?3.     

Radiation breakdown in silicon wafers

Radiation breakdown in silicon slabs is observed and studied as revealed in anomalous behavior of the dose characteristics of their radiation defects when the radiative intensity is varied. A theory is constructed for reversible radiation breakdown due to the bistability which develops in a gas of radiation vacancies when the gas can be regarded as quasi-two-dimensional. In order to explain the exponential saturation of the dose characteristics as the irradiation intensity is increased, scenarios are proposed in which different forms of the constituent radiation defects develop. Some parameters of the bistable gas of primary vacancies are estimated, including diffusion coefficients, dimensions of inhomogeneity regions, and the rate of movement of the stratification line. On the whole, satisfactory agreement with experiment is obtained. Discrepancies between the diffusion coefficient for neutral vacancies obtained here and in the literature are attributed to the role of interband recombination accompanying radiation defect formation during electron bombardment. Zh. éksp. Teor. Fiz. 114, 1067–1078 (September 1998)     

Dynamic properties of dislocations in silicon wafers heat-treated at low temperatures

The specific features of the dislocation motion in dislocation-free silicon wafers (single crystals are grown by the Czochralski method) heat-treated at 450 and 650°C have been investigated. It is found that the low-temperature treatment of silicon wafers with an oxygen content of (7–8)×10¹⁷ cm^?3 substantially affects the dynamic properties of dislocations generated into silicon wafers during their four-point bending and brings about an increase in the starting stresses of the onset of the dislocation motion. A characteristic spatial inhomogeneity is observed in the generation and propagation of dislocations from indentations upon the bending of heat-treated wafers. The reasons for the regularities revealed are discussed.     

Exciton-plasma Mott transition in CdSe at 77K

Photoluminescence spectra of CdSe obtained in conditions of moderate excitation densities show anomalies in the behavior of peak position and intensity. These anomalies, on the basis of the optical gain and in the shift of peak position to lower energy side, are ascribed to the onset of an exciton-plasma Mott-transition in the photoexcited semiconductor.     

Helical gold nanotube synthesized at 150 K

Gold nanowires were synthesized at 150 K by electron beam thinning of a gold thin foil in an UHV electron microscope. The gold nanowires were found to have a helical multishell structure (HMS). One particular nanowire, which was thinner than the 7-1 HMS nanowire, was found to have a tubular structure. The gold single wall nanotube is composed of five atomic rows that coil about the tube axis. The diameter was 0.4 nm and the pitch was 11 nm. The stability of the (5,3) nanotube was discussed in terms of the shear deformation of the triangular network of gold atoms.     

Fluorescence of para-diethynylbenzene in polycrystalline methylcyclohexane at 77 K

From analyses of the 77 K ¹B_2u → ¹A_g fluorescence of para-C₆H₄(CCH)₂ and para-C₆H₄(CCD)₂ it is concluded that the forbidden subspectrum, based on one quantum of b_3g vibrations, is predominant. Its appearance is in accord with predictions of Herzberg-Teller vibronic coupling theory.     

Helical instability in variband semiconductors

In this paper the characteristics of the helical instability in a semiconductor plate in which the width of the forbidden band varies linearly over the thickness are studied theoretically. The dependences of the threshold product of the external fields and the wave vector which arise at the threshold of instability of the disturbances on the gradient of the width of the forbidden band and the orientations of the external electric and magnetic fields are calculated. It is shown that nonuniformity of the band structure can result in a lower excitation threshold of instability than in the case of a homogeneous-band semiconductor.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 54–58, January, 1991.     

Neutron scattering study of NiHx at 77K

The results of simultaneous measurements of inelastic incoherent neutron scattering (IINS) and neutron diffraction on NiH_x system with x = 0.40, 0.28 and 0.12 at temperatures of 77 K are briefly presented. In the phonon density of states, supposing a one-phonon mechanism for the scattering process, the optic modes appear as a broad band from 70 to 140 meV with a strong peak at 90 meV and weak peaks at 105 and 130 meV. Neutron diffraction confirms information about the phase composition of the samples investigated.     

Radiolysis of vitreous cyclohexane-neohexane mixtures at 77 K

Vitreous mixtures of cyclohexane and neohexane were irradiated by gamma rays at 77 K. The relative radical concentrations were computed from E.S.R. spectra of the irradiated mixtures. A chemical activation transfer from the neohexane to the cyclohexane can explain the excess of cyclohexyl radicals with respect to the electron fraction.

An hydrogen transfer from neohexane to cyclohexyl radicals occurs at 120 K.     

纳米Ni在77 K温度下压缩行为的研究

利用低温力学测试系统研究了电化学沉积纳米Ni在77 K温度下的压缩行为. 室温下纳米Ni 的屈服强度为 2.0 GPa, 77 K温度下的屈服强度为3.0 GPa, 压缩变形量则由室温的10%左右下降到5%. 借助应变速率敏感指数、激活体积、扫描电子显微和高分辨透射电子显微分析, 对纳米Ni的塑性变形机制进行了表征. 研究表明, 在77 K温度下的塑性变形主要是由晶界-位错协调变形主导, 晶界本征位错弓出后无阻碍地在晶粒内无位错区运动, 直至在相对晶界发生类似切割林位错行为. 同时分析了弓出位错的残留位错部分在协调塑性变形时起到的增加应变相容性和减小应力集中的作用. 利用晶界-位错协调机制和残留位错运动与温度及缺陷的相关性揭示了纳米Ni室温和77 K温度压缩性能差异的内在原因. 关键词： 塑性变形 强度 位错     

Modulated photoreflectance characterization of ion-implanted semiconductor wafers

Modulated PhotoReflectance (MPR) measurements on semiconductor wafers implanted with boron or silicon ions in the dose range 5×10¹⁰–5×10¹⁵ ions/cm² are presented. Correspondingly, a one-dimensional theoretical multilayer model is established. In the theory, as the implant dose is lower than a critical value, the variation of the MPR signal is contributed mainly by the implanted defects and damages. However, when the dose is above the critical dose, the change of the MPR signal is chiefly due to the formation and growth of an amorphous layer. The theoretical results are in good agreement with those of experiments.