Raman spectroscopy of resonance exciton tunneling in GaAs/AlAs superlattices in electric fields

Optical-resonance-Raman scattering by acoustic phonons is used to study the effect of an electric field on the state of excitons in GaAs/AlAs superlattices. When the energy of the exciting photon coincides with the energy of an exciton bound to Wannier-Stark states of a heavy hole and electron with Δn=0,±1, the acoustic Raman scattering is enhanced. Oscillations in the intensity of the Raman spectrum in the electric field are explained by resonance delocalization of the exciton ground state as it interacts with Wannier-Stark states of neighboring quantum wells or with Wannier-Stark states of a higher electron miniband. Fiz. Tverd. Tela (St. Petersburg) 40, 827–829 (May 1998)     

Infrared and Raman spectra of M2Cu2O5 (M=Y,Ho)

We report both Raman and infrared reflectivity spectra of M₂Cu₂O₅ (M=Y, Ho) at room temperature in the spectral range of 30–1000 cm^–1.37 (31) ir and 18 (15) Raman active modes of Y₂Cu₂O₅ (Ho₂Cu₂O₅) are observed. A factor group analysis has been performed to identify the symmetries of the observed modes. Comparing the vibrational spectra of these compounds we conclude that the phonons above 300 cm^–1 originate from the Cu–O vibrations and those under 300 cm^–1 from M–O vibrations.Alexander von Humboldt Foundation fellow     

Stress-induced splitting of the conduction bands of GaAs and GaSb

The splitting induced by a [110] strain in the conduction bands of GaAs and GaSb can be obtained from the measured spin relaxation of photoexcited carriers. These experimental results are shown to be in satisfactory agreement with predictions based on $\text{k}$.$\text{p}$ perturbation theory, which use recently calculated values of the coupling between the Г₁ and the two nearest Г₁₅·bands induced by the strain.     

Raman scattering studies in phosphorus implanted and laser annealed boron doped Si

Implantation of P in B bulk doped Si (hole concentration = 2.1×10²⁰ cm^?3) followed by multiple pulse laser annealing with a XeCl laser has produced the incorporation of P in substitutional sites of the matrix and also charge carrier compensation. We report in this paper light scattering studies of these samples, in which a decrease of the hole-induced softening of the Si-Raman line is observed. This softening depends on the type and concentration of free carriers and thus, in our case, on the degree of compensation. This softening is discussed in terms of the interaction of the continuum of free carrier excitations with the Raman phonon. We also report the observation of the vibrations of ¹¹B-³¹ P pairs.     

Raman spectra of two new modifications of germanium: Allo-germanium and 4H-Ge

The Raman spectra of allogermanium and 4H germanium have been measured. Allogermanium shows a band which mimics the density of states of diamond-like Ge(Ge?I). 4H-Ge shows a peak at 287 cm^-1 which can be assigned to an E₂ phonon. This phonon corresponds to a TO-mode of Ge-I at the $\text{(}\text{π}\text{2}\text{a}\text{) (1|1)}$ point of the Brillouin zone.     

Resonant Raman scattering in germanium

We have studied the spectral dependence of the first order Raman scattering cross section of Ge at room and liquid nitrogen temperatures in the energy region containing the E₁ and E₁ + Δ₁ optical gaps. This region was covered by a fine mesh of points obtained from the discrete lines of three gas lasers and a cw continuously tunable dye laser. Only one resonant peak was observed, as opposed to the two peaks that characterise the absorption and reflection spectra in this region. The shape of this resonance peak can be explained as due to the changes in the electronic polarizability produced by phonon-induced wave function mixing of the spin-orbit split Λ valence band doublet. The observed temperature shift in the resonant energy is much smaller than the one predicted from the known shifts of the optical gaps with temperature. Furthermore the resonant peak at room temperature appears shifted to higher energies when compared with the theoretical peak calculated from the room temperature optical constants. The resonant Raman peak appears to shift with increasing temperature by the full thermal expansion effect plus only a fraction of the electron-phonon interaction shift seen in the optical constants.     

Internal strain parameter of silicon and GaAs and planar force constants

We show that the internal strain parameter ζ and elastic constants of the tetrahedral semiconductors can be determined from the force constants between planes of atoms. These have been computed recently for Si and GaAs from self-consistent electronic calculations using the Hellmann-Feynman theorem. The theoretical results are ζ = 0.72 for GaAs and ～0.57 for Si compared to experimental values of 0.76 and 0.73.     

Fine structure in optical transitions from 3d and 4d core levels to the lower conduction band in Ga-V and In-V compounds

We investigate fine structure in energy derivative reflectance (EDR) spectra near 20–21 eV in GaP, GaAs, and GaSb, and near 18–20 eV in InP, InAs, and InSb. Derived energy values for X^c₁ thresholds in GaP and GaSb, and L^c₁ and X^c₁ thresholds in GaAs, agree well with previous Schottky barrier electroreflectance (ER) results. L-X structure splittings in EDR spectra of InAs and InSb, for which Schottky barrier ER measurements cannot be performed, are 0.29 and 0.44 eV, respectively. Estimates of expected locations of these structures, based on XPS and absorption data and band structure calculations, indicate energy deficits of 0.2 eV for In4d-L^c₁ and 0.5 eV for In4d-X^c₁ transitions, respectively.     

Intrinsic piezobirefringence of several semiconducting chalcogenides

We have measured the piezobirefringence spectra of several II–VI compounds with zincblende (CdTe, ZnTe, ZnSe, ZnS) and wurtzite structure (CdS, ZnO) in the region of transparency. Similar studies have also been performed with rock-salt-type lead salts (PbS, PbTe). The results have been compared with theoretical prediction based on simplified models of the interband transitions and of the corresponding excitonic effects.     

Spin-orbit splitting of the copper halides and its volume dependence

We have investigated theoretically and experimentally the dependence of the spin-orbit splitting of the edge excitons in CuCl, CuBr, and CuI on volume. The results indicate a large contribution of the change in p(halogen)-d(Cu) hybridization with volume, especially for CuCl.