Tyuzi Ohyama

Cyclotron Resonance of Doped Silicon

Electron scattering and recombination studies through cyclotron resonance in doped silicon are carried out between 1.5 and 4.2°K. It is found that below 4.2°K the electron resonance linewidth for p -type silicon consists not only of scattering effect, but also of lifetime broadening. The latter can largely be eliminated on application of a strong uniaxial stress. So long as the scattering part is concerned, the observed features both for n -and for p -type materials are qualitatively explicable through the model of electron or positron scattering by a free hydrogen atom. Some discrepancies owing to the failure of the effective mass approach, however, are observed for all the dopants except for lithium. Analyses of temperature, stress and concentration dependence of electron lifetime in boron-doped silicon lead to the conclusion that the neutral boron impurities themselves are responsible for the carrier recombination.

Millimeter and Submillimeter Cyclotron Resonance Study of High-Purity ZnSe

We have observed for the first time the electron cyclotron resonance in a high quality ZnSe crystal, using both millimeter and submillimeter waves. We obtain an isotropic effective mass m*=0.145m0. From linewidth measurement it is found that the cyclotron mobility at 4.2 K exceeds 2.3×105 cm2/Vs. A strong anisotropy in absorption intensity has been observed in 35 GHz measurement.

Weak Localization and Correlation Effects of Two Dimensional Electrons in Indium-Tin-Oxide Films

We have studied the temperature and magnetic field dependence of conductance in the two dimensional electron system of indium-tin-oxide films at temperatures between 1.5 and 300 K and up to the magnetic field of 100 kOe. Evidence for localization as well as correlation effects, and that for two-to-three dimensional transition induced by the magnetic field are clearly observed. By precisely fitting the experimental data to the available theories, localization parameters α T and α H as well as the temperature dependence of the inelastic scattering time τ e are deduced. For thick films, localization features of the three dimensional system are also observed.

Weak Localization and Correlation Effects in Indium-Tin-Oxide Films. II. Two-to-Three Dimensional Transition and Competition between Localization and Superconductivity

A study was made of the temperature and magnetic field dependence of the conductivity in indium-tin-oxide (ITO) films for two and for three dimensional electron systems. Clear evidence of a three dimensional localization as well as Coulomb interaction effects is observed above 15 K in relatively thick samples (≥400 A). On application of a magnetic field, a two-to-three dimensional transition is observed above a critical field, that depends on the sample thickness. From the temperature dependence of conductivity for the thickest film (20000 A), it was found that ITO shows a superconducting nature below 3.5 K. For the sample with an intermediate thickness (1000 A), temperature and magnetic field dependence of conductivity is discussed from the view-point of the competition between electron localization and superconductivity.

Magneto-acoustic absorption by the electron-hole liquid in stressed germanium

Abstract We report the observation of magneto-acoustic absorption by the electron-hole liquid in a potential well in stressed germanium. This experiment confirms the metallic character of the liquid and yields direct values for the electron Fermi level ϵ F = (2.6±0.1) meV and inter-carrier collision time τ = (6.0±0.5) × 10 -11 sec at 1.8 K under a stress of approximately 5 kg/mm 2 . From ϵ F we deduce an electron density of n = (6.2) ± 0.4) × 10 16 cm -3 at 1.8 K.

Time-Resolved Cyclotron Resonance Analysis of Electron-Exciton Interaction in Silicon

Through time-resolved analysis, it has been concluded that the linewidth of cyclotron resonance for electrons in pure silicon crystal for a certain short interval of time after strong photo-excitation is primarily determined by interaction with isolated excitons. In combination with the work by Cuthbert, the magnitude of electron-exciton interaction is estimated. It lies between those of electron-neutral donor and electron-neutral acceptor interactions.

Residual Donor Impurities in MO-CVD Gallium Arsenide

Residual donor species as well as their concentrations in undoped MO-CVD GaAs have been investigated using far-infrared laser magneto-optics with intrinsic photoexcitation. Both donor and acceptor concentrations have been precisely determined for various samples grown under different conditions. It has been found that the main donor species in MO-CVD GaAs are Si and Ge, the relative concentrations of which depend on the partial pressure of AsH3.

Quantum Transport Study of Silicon and Germanium by 4-mm Wave Cyclotron Resonance below 1°K

Electron scattering by phonons and neutral impurities as well as electron capture by the latter in silicon and germanium have been studied between 0.5 and 4.2°K through He 3 -coolant at the frequency of 71 GHz. The scattering relaxation time by phonons in ultra-high purity materials is compared with the calculation by Ito et al. and by Meyer. In addition, a spin polarization effect on neutral impurity scattering at the quantum limit, \(\hbar\omega_{\text{s}}{>}k_{\text{B}}T\), has been studied for n -type materials. This problem has been treated in a way similar to the e - -H atomic scattering and a simple analytical calculation for the scattering of spin polarized electrons by spin polarized donors is carried out on the basis of Schwartzs work. This calculation yields an essential agreement with the experimental results. For silicon doped with phosphorus and germanium doped with indium, spin polarization effects on electron capture by neutral impurity are observed.

Dynamical Behaviour of Photoexcited Electron System in Gallium Arsenide

In this work we report on the first observation of the far-infrared Baser (119–220 µm) magneto-optical absorption by the photoexcited electron system in GaAs up to the magnetic field of 50 kG over the temperature range of 1.7–4.2 K. The major absorption lines observed for various samples are the 1s→2p +1 . Zeeman transition and the cyclotron resonance of conduction electrons. It is found that both absorption line-widths are sensitive to impurity concentration and to conduction electron density. The magnitude of the electron-electron scattering and that of the electron-neutral impurity scattering under the quantum limit condition are thereby discussed.

Structured photoluminescence spectrum in laterally anodized porous silicon

Visible photoluminescence (PL) has been systematically investigated in laterally anodized porous silicon. The PL peak position was dependent on the distance from the meniscus and shifted towards a shorter wavelength with increasing anodization current density. A PL spectrum exhibiting several structures was observed inside the mirrorlike region on the sample surface, which was interpreted by multiple reflection of the luminescence, not by the quantum size effects. Through the analysis of the PL spectrum, the Si density of the porous layer was roughly estimated to be 37% by means of the effective-medium model.