T. Ohyama

Line-Width of Quantum Limit Cyclotron Resonance. I. Phonon Scatterings in Ge, Si, CdS and InSb

Studies of the Cyclotron Resonance Line-Width (CRLW) in the quantum limit have been made for phonon scatterings in basic semiconductors (Ge, Si, CdS and InSb). The acoustic deformation potential scattering has been examined for Ge and Si, while the acoustic piezo-electric scattering for CdS. The effect of the inelastic scattering is enhanced in the quantum limit. Furthermore, the spontaneous acoustic phonon emission is clearly affecting CRLW. Temperature dependences of CRLW for deformation potential and piezo-electric scatterings are similar to each other. Difference, however, arises in the magnetic field dependence. With regard to polar optical phonon scatterings, it has been confirmed for InSb that CRLW is dominated by the absorption part.

Natural quantum wells in ZnSe

Abstract Microwave cyclotron resonance has been observed in various ZnSe crystals with different heat-treatments, as a function of magnetic field orientation, temperature and delay time after photo-pulse excitation. The two-dimensional (2D) character of the absorption signal consistently shows up. X-ray analysis and microscopic observation with polarizers reveal a beautiful multimosaic structure of numberless twin crystal boundaries for all samples. These boundaries are evidently leading to a formation of natural quantum wells that are responsible for the 2D characters.

Magnetic field dependence of spontaneous oscillation in n-InSb

The magnetic field dependence of spontaneous oscillation in n-InSb is investigated. We have observed two types of variation in the oscillation with increasing magnetic field. One is an abrupt appearance of the oscillation between 0.56 T and 0.68 T. The other is the appearance of bifurcation in the oscillation period above 0.79 T. This can be explained by the change of the number of levels in the electron system, according to the generation-recombination model of Schöll for the self-generated chaos. The magnitude of the current at the onset of the oscillation decreases linearly with increasing magnetic field.

Far-infrared study of excitons, electron-hole drops, and impurity systems in germanium

Decay kinetics of exciton and electron-hole drop systems in a highly photoexcited germanium crystal are investigated by observing time-resolved far-infrared laser magnetoabsorption. Magnetospectroscopy of indium-doped material is also studied over 48-220 μm.

Crossover from positive to negative magnetoresistance by the rise of electron temperature for Si:Sb in the variable-range hopping regime

Abstract Magnetoresistance (MR) measurements in Si:Sb with the Sb concentration just below the critical concentration for metal–insulator transition have been carried out by stepping into the non-ohmic region of the electric current density. We have found that the MR sensitively depends on the electric current density. For the insulating sample positive MR is observed in the low current density region. A crossover from positive to negative MR is found as the current density increases. It is considered that these phenomena originate from the rise of the electron temperature and are related to the transport in the upper-Hubbard band.

Weak Localization and Weak Anti‐Localization in Polycrystalline In2O3—x Thin Films Grown by Sputtering Method

Weak localization (WL) and weak anti-localization (WAL) phenomena in polycrystalline In 2 O 3-x thin films grown by sputtering have been studied on the magneto-conductance (MC) before and after the heat treatment, as functions of the temperature, the magnetic field, the azimuth of magnetic field and the film thickness (10-60 nm). The WL profile in MC undergoes a drastic change by the heat treatment above 350 °C and the WAL phenomena become remarkable with increasing temperature. It has been concluded that the WAL arises from the spin-orbit scattering by the excess indium atoms through the elimination of oxygen atoms from the indium oxide by the heat treatment.

Broadening of Exciton Luminescence Line in Modified CdTe/ZnTe Multi-Quantum Wells

Photoluminescence in modified CdTe/ZnTe superlattice multi-quantum wells (MQWs) was investigated. In order to reduce the number of misfit dislocations, the well region is formed from a short-period strained-layer superlattice composed of CdTe and ZnTe. The observed peak energies of the free exciton line are higher than those calculated. The full width at half-maximum of the observed line has a minimum around 45 K in the temperature range between 1.8 and 210 K. The broadening above 45 K is attributed to exciton scattering with phonons and ionized impurities, while the broadening below 45 K is due to localized states.

Optically detected cyclotron resonance in Ge and Si exchange interaction in impact dissociation

We have investigated optically detected cyclotron resonance (ODCR) and ordinary cyclotron resonance (CR) under the same condition, in Ge and Si, which include both high-purity and doped samples. In impact dissociation processes, which are the origin of ODCR, donorbound excitons have larger cross section for impinging electrons than for holes, and conversely, acceptor- bound excitons have larger cross section for holes than for electrons. Moreover, the ratio of impact dissociation cross section for holes to that for electrons varies with the number of excitons bound to an impurity. These phenomena are understood primarily in terms of exchange interaction between impinging carriers and constituents of bound excitons. In addition, it is found that the relative intensity of hole cyclotron resonance against electron resonance is larger in ODCR than in CR. This is understood in terms of exchange interaction by taking the many valley nature of the conduction band into account.

Line-Width of Quantum Limit Cyclotron Resonance. II. Impurity and Carrier-Carrier Scatterings in Ge, InSb and GaAs

Cyclotron Resonance Line-Width (CRLW) has been studied in the quantum limit for impurity and carrier-carrier scatterings in Ge, InSb and GaAs. Ionized impurity and neutral impurity (electron-neutral donor and electron-neutral acceptor) scatterings have been examined with impurity scatterings. The dependences on temperature and magnetic field of CRLW for these two scatterings are similar to each other. From our experimental results it becomes clear that CRLW is approximately (1) independent of temperature and (2) proportional to the inverse of the square root of magnetic field. Electron momentum cross section by neutral acceptor is noted to be some orders of magnitude less as compared with that by neutral donor even in the quantum limit.

Quantum limit cyclotron resonance in p-GaAs

Abstract Electron scattering by neutral acceptors has been studied through far infrared (λ=172 μm) cyclotron resonance on p-GaAs at 4.2 K. It is found that (1) The inverse relaxation time is considerably smaller in the quantum limit than that predicted by D.C. transport theory in the absence of a magnetic field. (2) The same increase linearly with neutral acceptor concentration. (3) The electron momentum transfer cross section by neutral acceptor is by more than an order of magnitude smaller than that by neutral donor even in the quantum limit.