Measurement of minority carrier lifetimes in semiconductors

The bulk lifetimes of minority ,carriers in n-type l :germanium, in both n and p-type silicon and in n-type magnesium germanide have been investigated at room temperature. The sample was illuminated with periodic light ·flashes produced by a spark gap. The transient change in conductance of the sample after illumination gave the lifetime. In germanium and silicon the measured bulk lifetimes had values from 15 to 140 microseconds with estimated errors of 4 to 15 per cent, respectively. It was not possible to measure the lifetime in magnesium germanide because the particular sample used in this experiment was not sufficiently pure. The general solution of the equation of continuity for the minority carriers in a .rectangular sample has been obtained. The particular solution for the boundary and initial conditions of this experiment is discussed

Quantum Theory of Interband Faraday and Voigt Effects

A quantum-mechanical analysis of the Faraday rotation and the Voigt effect has been carried out for both the oscillatory and long-wavelength regions. Expressions have been developed for these effects from the off-diagonal and diagonal components, respectively, of the conductivity tensor ; the latter has been obtained in the form of the Kramers-Heisenberg dispersion relations through the use of first-order time-dependent perturbation theory. The results, which have been calculated for a simplified two-band model, are generalized to apply in the high-field case as well as the low-field limit. Through the introduction of a phenomenological relaxation time, γ, line shapes have been calculated for both the direct and indirect transition for the Faraday and Voigt effects. These have been obtained as a function of frequency for various values of magnetic field and relaxation times. The results obtained enable the evaluation of g factors from experimental line shapes

Far-Infrared Investigation on Structure of Amorphous Selenium

The structural ordering in various forms of amorphous selenium has been studied by means of far-infrared measurements on the two types of spectrum, corresponding to the Se^8-ring component and the polymeric chain. The chemical extraction method of the Se^8-ring component by CS_2 is re-examined in terms of the spectroscopic analysis which shows that the ring component can not be extracted entirely from the mixture of the ring and the chain. A polycrystalline trigonal selenium is obtained from the component extracted from the vitreous selenium quenched at a high temperature above 700℃. Black amorphous selenium is obtained by heat treatment of red one. The spectra for both of the amorphous states show that they consist of similar mixtures of the ring and the chain components, so that the transition from red to black does not correspond to the structural change from the ring to the chain nor vice versa

Phonon Structures in Optical Spectra of Layer Compounds GaSe and GaS

The infrared and far-infrared absorption spectra of β-GaSe and GaS have been measured in the temperature range from 50 to 300°K for the radiation polarized perpendicular to the c-axis in the hexagonal layer structure of these compounds. The reststrahlen frequencies measured at room temperature are 211.0 cm^ in β-GaSe and about 310 cm^ in GaS, respectively. In addition, the weak absorptions in the wave number range from 400 cm^ to 750 cm^ are identified with the multiphonon absorptions in the light of group theoretical analysis and of the experimental results on the Raman effect and on the electro-luminescence available up to date. The absorption line at 512 cm^ and band around 450 cm^ in β-GaSe are explained in terms of the localized mode of lattice vibrations induced possibly by an oxygen impurity. This analysis is the first preliminary investigation on the localized mode in a diatomic crystal of hexagonal structure

ジバチュウ ノ スイソ ゲンシヨウ レイキシ ノ ハドウ カンスウ ニ ツイテ ノ セツメンスウ ホゾンソク ノ ダトウセイ

Magnetoabsorption experiments on the A exciton in InSe have been performed in search of a unified correspondence relation between low and high magnetic field levels of a hydrogenlike state. Results show that the nodal-surface conservation rule of Shinada et al. is a more appropriate representation of this relationship than the so-called noncrossing rule.磁場中の水素原子の固有状態は解析的に解くことが不可能であるために、物理学上の永年の問題となってきた。磁場の強さが無限大の極限では無磁場のときとは量子数の全く異なる漸近解を持つことが知られているが、この強磁場極限準位に無磁場状態がどのように接続するかという疑問が問題の核心である。本研究では、InSeの励起子が物理的に理想に近い水素原子類似体であり、かつ固体効果によって水素原子に対するよりも数桁低い磁場で強磁場極限に到達しうることに着目して磁気光吸収を測定した結果、準位の接続に関して波動関数の節面数保存仮説を強く支持するデータが得られた

Raman Scattering of Inorganic Fibers

We have examined evolution of Raman spectra of carbon fibers and SiC fibers through structural transformations caused by heat treatment. Raman spectra of the SiC fibers indicate that the fibers consist of amorphous or microcrystalline SiC and graphitic microcrystals. We discuss the correlation between the tensile strength of the fibers and their microscopic structure deduced from the Raman data

Infrared Absorption and Faraday Effect in PbTe and PbSe

Free carrier absorption and Faraday effect in p-type PbSe, n- and p-type PbTe were measured in the wavelength range from 3 to 15 microns at room temperatures. The effective masses of electrons for PbTe and of holes for PbSe were deduced to be 0.11 m_0 and 0.14 m_0, respectively, and the ratios of the longitudinal to the transverse masses associated with the ellipsoidal energy surfaces were evaluated. It was concluded that four equivalent extrema exist along directions on the hole energy surface of PbSe, and this result is consistent with the similarity between the absorption characteristics of p-type PbSe and that of n-type PbTe

Vibrational Modes of C_<60> Fullerene Adsorbed on Si(100)2×1 Surface Studied by High-Resolution Electron-Energy-Loss Spectroscopy

We have measured the inelastic electron-energy-loss spectra of C_ on the Si(100)2x1 surface in the infra-red energy range. If C_ is evaporated 5Å (approximately half a monolayer) on Si(100), a strong energy loss peak appears at 65 meV, and weak peaks and shoulders at 72, 144, and 175 meV. In the 12Å thick film, additional weak peaks at 96, 160, and 189 meV become more apparent. Intensities of these peaks are comparable to those of thick films measured by infra-red absorption and by Raman scattering spectroscopies. Moreover, we have measured the angle dependence of the inelastic electron intensity. These results suggest appreciable interactions between C_ and the dangling bonds of Si surface

Rectangular Arrangement of Se-Ring Clusters on Graphite Surface and Their Structural Transformation

Ring-type Se clusters have been deposited on the C-plane of a graphite crystal and examined by STM images which were found to consist of 0.72nm×0.85nm rectangular lattices with individual molecules of 0.53nm in diameter. Se ring-type clusters sitting on each lattice point are most probably 6-membered. The STM images were taken with the bias voltage V_T between probe vs. sample as a parameter. For -0.7V<V_T<+0.7V the patterns of the rectangular lattice remains similar, but an order-disorder transition takes place at -0.065V; whereas V_T at -0.7V, the regular arrangement suddenly collapses to a random distribution of larger clusters consisting of their diameter in a range up to 5nm. The process of the structural change in the lattice system is not reversible with respect to the bias voltage. These experimental results are well explained by flrst-principles theoretical calculation on the structure and electronic properties of Se cluster using the DV-SCM method