H. Kobori

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.

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.

Weak Anti-Localization in?-Doped Sb Layer of Si

The spin-orbit (SO) interaction in a 6-doped Si: Sb with 0.11 monolayer of Sb atoms is studied, based on the first observation of the positive magnetoresistance in weak perpendicular magnetic fields due to the two-dimensional weak anti-localization in this system. From the fits of the magnetoconductance data in fields perpendicular to the layer, the SO scattering time τ so as well as the inelastic scattering time τ in have been extracted as τ so 3 × 10 -11 s and τ in T -1 , respectively. The ratio is τ so /4τ in 0.60 at T = 3 K, which is larger than any other value reported, indicating that the strength of the SO interaction in Si: Sb with 0.1 monolayer of Sb is very small compared with the ones found in the thin metal films.

Quantum magneto-optical oscillation on far-infrared Zeeman spectrum of n-InP

Abstract An oscillatory absorption spectrum which could not be detected in thin samples was observed for FIR magneto-optical absorption measurements in bulk n-InP at 4.2 K . It was found that the peak positions of the oscillation did not correspond to a series of direct transitions from the 1s ground state of donors into the Landau levels, and these peak positions considerably changed with the donor concentration. We have concluded that those oscillations are associated with a series of transitions from the 1s ground state into donor bands formed by the excited states and their accompanying the Landau levels.

Magnetic field dependence of polaron mass in CdTe

Abstract Polaron cyclotron resonance experiments are performed for high-quality CdTe samples at 4.2 K by use of far-infrared lasers. To study the polaron effect in a magnetic field precisely, various far-infrared wavelengths (513, 419, 394, 295, 220 and 172 microm) are employed on the conditions of photo- and electric field excitations. The polaron mass is obtained as a function of magnetic field for the n=0→n=1 ( n: Landau quantum number) and n=1→n=2 cyclotron resonance transitions. Regarding the n=0→n=1 transition, the experimental results are in good agreement with the theoretical prediction of F. M. Peeters and J.T. Devreese.

Quantum limit cyclotron resonance in Ge — acoustic deformation potential scattering —

Abstract Electron cyclotron resonance linewidth in pure Ge has been studied for acoustic deformation potential scattering in the quantum limit. The relaxation time derived therefrom is obtained as a function of temperature (10 to 160 K) and magnetic field (17 to 75 kG). The inverse relaxation time for acoustic deformation potential scattering in the quantum limit is found to be proportional to temperature and to the square root of the magnetic field. These experimental results are explained qualitatively by Meyers prediction.

MAGNETIC-FIELD-INDUCED NARROWING OF FAR-INFRARED MAGNETO-OPTICAL ABSORPTION OF NEUTRAL DONORS IN GAAS

Abstract We have studied the magnetic-field-induced narrowing of far-infrared (FIR) magneto optical absorption line for is-2p +1 transition of hydrogenic shallow donors in n-GaAs, of which line-width is dominated by the concentration broadening. The concentration range of donor is 1.5 × 10 15 cm −3 to 6.0 × 10 16 cm −3 , which extends over the concentration for occurrence of metal-insulator transition (Molt transition), i.e., 1.6 × 10 16 cm −3 . The linewidth narrowing due to magnetic field is considered to arise from the strong shrinkage of 2p +1 state.

Magnetic-field-induced two- to three-dimensional transition in weak localization and weak anti-localization regimes for In2O3−x thin films

We have extensively studied the magnetic-field-induced two- to three-dimensional transition in degenerated electronic systems in the weak localization and weak anti-localization regimes for polycrystalline In2O3−x thin films grown by the sputtering method. The magneto-conductance has been measured as functions of the temperature, the magnetic field, the azimuth of the magnetic field for the film surface and the film thickness (100, 150, 450 and 600A).

Electromotive force generation due to electron and impurity cyclotron resonances in compound semiconductors

We report on the resonant-photoelectromagnetic (R-PEM) effect in semiconductor, that is the electromotive force generation associated with electron cyclotron resonance (ECR) and impurity cyclotron resonance (ICR). This can be explained with a model that the carriers excited by the resonant absorption of the radiation induce the DC voltage through the thermomagnetic process. In this study, we have applied this technique to the n-InGaAs thin film and observed the negative voltage peak in addition to the usual positive ICR one. From the temperature variation and the resonant magnetic field dependence of these signals, we have concluded that the negative signal is induced by the ECR absorption. In addition, we have confirmed that the inversion of polarity for these signals originates in the inhomogeneous distribution of conduction electrons inside the film, and electrons localized at a fraction of the sample mainly cause the resonant absorption. Through the detailed observation and analysis of the generated DC voltage, we can investigate the dynamics of hot carriers inhomogeneously excited in the sample by the ECR as well as the ICR. Moreover, if we pay special attention to the polarity of the generated voltage, we can determine the distribution of electrons and impurities inside the film.

Intensive far-infrared optical study on the donor impurity band in the presence of a magnetic field for n-GaAs

Abstract We have intensively studied donor impurity bands formed by the ground and excited states in the presence of a magnetic field by means of the far-infrared optical technique. With this view, we have carried out measurements of the impurity cyclotron resonance absorption (ICRA) for hydrogenic donors in n-GaAs. Concerning the optical transition between the 1s and 2p +1 states, the variation of the full-width at half-maximum (FWHM) for the ICRA has been investigated as functions of the donor concentration and the magnetic field. Those dependencies of the FWHM have been discussed in consideration of energy bandwidths of the 1s and 2p +1 states for donors in the presence of a magnetic field. The energy bandwidths have been estimated by use of the tight binding approximation for the linear combinations of atomic orbitals, assuming the simple cubic configuration of donors. The qualitative agreement between experimental results and numerical estimation has been obtained.