Cu-Doping Effects in CdI2Nanocrystals: The Role of Cu-Agglomerates

Cu-doping effects in CdI2nanocrystals are studied experimentally. We use the photostimulated second harmonic generation (PSSHG) as a tool to investigate the effects. It is found that the PSSHG increases with increasing Cu content up to 0.6% and then decreases due to the formation of the Cu-agglomerates. The PSSHG for the crystal with Cu content higher than 1% reduces to that for the undoped CdI2crystal. The results suggest that a crucial role of the Cu-metallic agglomerates is involved in the processes as responsible for the observed effects

Electron-Spin Precession in Dependence of the Orientation of the External Magnetic Field

Electron-spin dynamics in semiconductor-based heterostructures has been investigated in oblique magnetic fields. Spins are generated optically by a circularly polarized light, and the dynamics of spins in dependence of the orientation (θ) of the magnetic field are studied. The electron-spin precession frequency, polarization amplitude, and decay rate as a function ofθare obtained and the reasons for their dependences are discussed. From the measured data, the values of the longitudinal and transverse components of the electrong-factor are estimated and are found to be in good agreement with those obtained in earlier investigations. The possible mechanisms responsible for the observed effects are also discussed

Photo-Induced Spin Dynamics in Semiconductor Quantum Wells

We experimentally investigate the dynamics of spins in GaAs quantum wells under applied electric bias by photoluminescence (PL) measurements excited with circularly polarized light. The bias-dependent circular polarization of PL (PPL) with and without magnetic field is studied. ThePPLwithout magnetic field is found to be decayed with an enhancement of increasing the strength of the negative bias. However,PPLin a transverse magnetic field shows oscillations under an electric bias, indicating that the precession of electron spin occurs in quantum wells. The results are discussed based on the electron–hole exchange interaction in the electric field

Energy and spin relaxations in drift transport of carriers: effects of polar optical hot phonon generation

We study the energy and spin relaxations in drift transport of electrons in n-doped GaAs. Stating from the rate of change of phonon occupancy in a relaxation time approximation and the electronic power dissipated in a drifted Maxwellian distribution, the hot phonon generation in high field transport and its effect in electronic spin relaxation are investigated. The scattering is confined to polar optical phonon incorporated by implementing the Ehrenreich’s variational approach in the scattering process. It is found that a finite phonon lifetime can reduce the energy relaxation rate and hence can increase the momentum relaxation rate, resulting in lowering the mobility or delaying the runaway to higher fields, where the effect increases with electron density. The electron spin is found to relax with a frequency of sub-THz, and the spin lifetime (τs) is found to decrease with increasing the strength of the drifting field. However, a high field completely depolarizes the electron spin due to an increase of the spin precession frequency of the hot electrons via the longitudinal polar optical phonon scattering. It is also found that τs increases with increasing the moderately n-doping density up to about 1 × 1017 cm−3 or decreasing the crystal temperature. However, a high density decreases it abruptly. The results are discussed on the basis of the Dyakonov–Perel (DP) spin relaxation mechanism

Spin drift and spin diffusion currents in semiconductors

On the basis of a spin drift-diffusion model, we show how the spin current is composed and find that spin drift and spin diffusion contribute additively to the spin current, where the spin diffusion current decreases with electric field while the spin drift current increases, demonstrating that the extension of the spin diffusion length by a strong field does not result in a significant increase in spin current in semiconductors owing to the competing effect of the electric field on diffusion. We also find that there is a spin drift-diffusion crossover field for a process in which the drift and diffusion contribute equally to the spin current, which suggests a possible method of identifying whether the process for a given electric field is in the spin drift or spin diffusion regime. Spin drift-diffusion crossover fields for GaAs are calculated and are found to be quite small. We derive the relations between intrinsic spin diffusion length and the spin drift-diffusion crossover field of a semiconductor for different electron statistical regimes. The findings resulting from this investigation might be important for semiconductor spintronics