Tatsuya Tomaru

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.

Optically Detected Cyclotron Resonance of Exciton and Electron-Hole Droplet Systems in Pure Germanium

Optically detected cyclotron resonance (ODCR) in pure-Ge has been observed. Experimental results are (1) hole resonance has been observed stronger at ODCR than at usual cyclotron resonance (CR), (2) effective mass dependence of signal intensity of electron resonance at ODCR is different from one at CR, and (3) both free carrier-exciton and free carrier-exciton-electron hole droplet coexisting systems are not expressed by a single carrier temperature when free carriers are rather hot through microwave absorption. By means of kinetic equations it is shown that the origin of ODCR observation is the impact ionization of excitons by free carriers in the free carrier-exciton coexisting system.

Dynamics and Kinetics of Carrier System in Photoexcited Ge and Si Observed by Optically Detected Cyclotron Resonance

We have observed optically detected cyclotron resonance (ODCR) in Ge and Si. Complicated but outstanding signals have been observed in As-doped Ge. They are explained on the basis of our results obtained earlier. As for Si, kinetics of a system consisting of free carriers, free and bound excitons, bound multiexciton complexes and electron-hole droplets under cyclotron resonance condition is analyzed by means of rate equations, together with “effective temperature” introduced. Besides, the change in photoluminescence spectrum caused by cyclotron resonance is compared with that caused by DC electric field, where a new advantage of ODCR is found.

Quasi-Adiabatic Quantum Computing Treated with c-Numbers Using the Local-Field Response

A computational method called the local-field response method is proposed, where spins evolve by responding to an effective field consisting of gradually decreasing external fields and spin–spin interactions, similarly to what is carried out in adiabatic quantum computing (AQC). This method is partly quantum–mechanical. That is, spins are treated as classical variables, but the response function of the spins to the effective field is determined a priori by referring to a quantum–mechanical calculation that was carried out for similar problems. This novel response function improves the performance of the ground state being maintained in the time evolution compared with the case without a priori information. The performance is numerically checked in an eight-qubit system by solving random-interaction problems of finding their ground states. The false probability decreases by about half as a result of using a priori information. The operation of this method is classical, but it has a quantum–mechanical advan...

Optically detected cyclotron resonance in Ge, Si and ZnSe

Abstract We have investigated optically detected cyclotron resonance (ODCR) and ordinary cyclotron resonance (CR) under the same excitation condition, in Ge, Si and ZnSe, which include both high-purity and doped materials. We have discussed various new features about the impact dissociation process for excitons, bound excitons, bound-multiple-exciton-complex and electron-hole droplets, which are the origin of ODCR. In addition, some information related to hot-electron distribution induced by CR are obtained through the ODCR spectra.

Wavenumber distribution of hot holes under the cyclotron resonance condition-striking enhancement of harmonics in optically detected cyclotron resonance

Harmonics of hole cyclotron resonance are more pronounced in optically detected cyclotron resonance than in ordinary cyclotron resonance. Thanks to this enhancement, harmonics have been clearly observed to the third order for light holes and to the sixth order for heavy holes Ge. This phenomenon is explained by consideration of the wavenumber distribution of hot holes produced by cyclotron resonance and its harmonics.

Magnetic Field Dependence of Carrier and Exciton Diffusion in Photoexcited Ge

To investigate the magnetic field dependence of the carrier diffusion, the nonequilibrium electron-exciton system in photoexcited Ge is studied. Three types of experiments are performed, that is, a time resolved magneto-optical absorption measurement employing a far infrared laser and the same employing microwaves, and a space-resolved luminescence measurement without applying a magnetic field. It is found that 1) a quasi-equilibrium relation between free carriers and excitons exists. 2) The diffusion coefficient clearly decreases with increasing magnetic field. 3) This magnetic field dependence can be explained qualitatively by the random walk model of electrons.

Local Field Response Method Phenomenologically Introducing Spin Correlations

The local field response (LFR) method is a way of searching for the ground state in a similar manner to quantum annealing. However, the LFR method operates on a classical machine, and quantum effec...

USING OPTICALLY DETECTED CYCLOTRON RESONANCE TO STUDY ELECTRON-EXCITON AND ELECTRON-PHONON INTERACTIONS IN SEMICONDUCTORS

We review our optically detected cyclotron resonance (ODCR) studies extending over Ge, Si and ZnSe. The following three subjects are taken up: (1) Impact dissociation of excitons by free carriers, which is dominated by electron-electron and hole-hole interactions rather than by electron-hole interaction. (2) The hot-carrier state produced in Ge and Si by cyclotron resonance is discussed in terms of hot-carrier-distribution function, effective carrier temperature, and carrier kinetics. (3) The relaxation process of photoexcited carriers in ZnSe is discussed. This relaxation process is found to be dominated by electron-polar-optical-phonon interaction, which gives rise to the polaron effect and to resonant formation of free excitons following one-LO-phonon emission. Thermally detected cyclotron resonance (TDCR) is also introduced.