Manuel Cardona

Spatial dispersion in the dielectric constant of GaAs

Abstract Birefringence in single crystal GaAs due to the dependence (or spatial dispersion) of the dielectric constant has been measured from 0.95 μ to 1.8 μ. Considerable enhancement was observed as the absorption edge was approached. The observed temporal dispersion in the birefringence was found to agree well with the prediction of a 4-band model involving no adjustable parameters. Within a model a direct relation was found to exist between the frequency dependence of the spatial dispersion and the warping of the J = 3 2 valence bands.

Valence band symmetry and deformation potentials of ZnO

Abstract The negative spin-orbit splitting of the valence band at k = 0 in ZnO, as proposed by Thomas and Hopfield, has been confirmed experimentally by measuring the effect of static uniaxial compression along the c-axis on the exciton spectrum of ZnO at 77°K. Four deformation potentials have been determined and are compared with the previously obtained values for CdS.

Intrinsic piezobirefringence of several semiconducting chalcogenides

Abstract 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.

Volume dependence of the Raman frequencies of GeSi alloys

Abstract We have measured the shift of the three main Raman peaks of several germanium-silicon alloys upon application of hydrostatic pressure. The frequency associated with Geue5f8Si pairs has a mode Gruneisen constant γGeue5f8Si = 1.20 ± 0.04, higher than that of the Raman frequency of either pure constituent. The Gruneisen constants of the Raman frequencies of Geue5f8Ge and Siue5f8Si pairs also increase from the value for the pure elements when approaching the 50% concentration, reaching the values γGeue5f8Ge = 1.31 ± 0.1 and γSiue5f8Si = 1.24 ± 0.02 for Ge0.46 Si0.54. This increase is due to the fact that the dominant eigenstates of the vibration shift from κ = 0 to the edge of the zone with increasing disorder.

Transverse electroreflectance in semi-insulating silicon and gallium arsenide

Abstract The transverse electroreflectance (TER) spectrum of GaAs is measured over an energy range extending from the fundamental absorption edge to the lambda structure. The TER structure in the vicinity of 3.4eV in Si is also presented. Quantitative measurements of the variation of the spectrum with field have been performed, utilizing the facts that the TER geometry permits the calculation of the value of the electric field, and that the field is essentially uniform in the region of measurement. A detailed investigation of the effect of collision broadening on the electroreflectance response in the one-electron approximation is given, which qualitatively correlates the dependence of peak amplitude, peak location, and number of subsidiary oscillations observed in electroreflectance with the magnitude of the field and collision broadening lifetime. A method of measuring the collision broadening lifetime is applied to the fundamental edge of the GaAs sample used in this experiment. A conformal mapping is presented which enables a calculation of the field at any position in the crystal for the common TER geometries.

Photoreflectance and electroreflectance in silicon

Abstract The photoreflectance spectrum of the 3.4 eV peak of a [110] silicon surface shows a dependence on the polarization of the probing light analogous to that found for the electroreflectance spectrum. Photoreflectance measurements in the presence of externally applied surface dc electric fields show a marked increase in the intensity of the peaks when the external field is in a direction such that it increases the band bending at the semiconductor surface. The reciprocal effect, cancellation of the electroreflectance spectrum by means of a secondary light beam, has also been observed. We conclude that the photoreflectance is the electroreflectance produced by the quenching of the surface fields by photoexcited electron-hole pairs.

Energy band structure of germanium and gallium arsenide: The k.p method☆

Abstract The energy bands of germanium, valid throughout the entire Brillouin zone, have been obtained by diagonalizing a k . p Hamiltonian referred to 15 states at k = 0. The band structure of GaAs has been calculated by adding six independent matrix elements of an antisymmetric potential V − to the 15 × 15 k . p Hamiltonian of germanium.

Electroreflectance and band structure of gray tin

Abstract The electroreflectance spectrum of gray tin in the 1–5 eV region is reported. Nine peaks are observed and assigned to direct interband transitions at critical points. A semiempirical band structure, calculated with due regard of spin-orbit interaction by the k . p . method, incorporating the electroreflectance gaps and the Groves-Paul model is presented.

Electronic surface states in germanium and silicon

Abstract The energy bands of silicon for imaginary values of k are obtained by diagonalizing a 15 × 15 k . p Hamiltonian. The results are compared with those of the two band model. A method is given to calculate intrinsic surface states using these bands. The results of preliminary calculations for silicon are presented.

Band structure of gray tin under uniaxial stress

Abstract Gray tin, a perfect semimetal, becomes a semiconductor under uniaxial stress. The lowest conduction band minimum at k = 0 becomes strongly anisotropic. The valence band of the compressed material has highest maxima away from k = 0 ; toroidal constant energy surfaces are obtained for [111] and for [100] compression.