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

Induction strategies of the noncentrosymmetricity in centrosymmetric nonlinear optical nanocrystal processes

The second harmonic generation (SHG) is one of the measures of the optical nonlinearity. However, the SHG is prevented by symmetry in a centrosymmetric material. Therefore, in order to observe the SHG it is necessary to form a noncentrosymmetric process in a centrosymmetric material. Noncentrosymmetric nanosize-material processes CdI2 are formed by doping it with the impurity copper, controlling the size of the crystal and crystal temperature, and by pumping with an IR laser beam. The noncentrosymmetricity in the processes are probed by the observation of SHG and the second-order optical susceptibility ( χijk(2) χijk(2) ) is calculated from the SHG data. The value of χijk(2) χijk(2) is found to depend fashionably on the impurity content of the nanomaterials: χijk(2) = C1 exp[-1∕2{(Si-C2)∕C3}2] χijk(2)=C1 exp[-1∕2{(Si-C2)∕C3}2] , where Si is the concentration of impurity of the type i (here Si is SCu), and C1, C2 and C3 are parameters whose values depend on the crystal temperature and thickness of the nanomaterials. A photoluminescence measurement supports the third-order nonlinearity ( χijkl(3) χijkl(3) ) of the centrosymmetric CdI2 system and hence SHG in the induced processes. The results also show that a significant enhancement (from 0.37 pm/V to 0.83 pm/V) in the noncentrosymmetric response χijk(2) χijk(2) is achieved in nanomaterials with reduced sizes and at low temperatures. A recipe of the induction strategies of the noncentrosymmetricity in centrosymmetric nonlinear optical processes CdI2 is explored and the results are discussed. However, the findings resulting from this investigation show that cadmium iodide nanocrystals might have potential in applications as optoelectronic nanodevices

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