Crystal-field Split-off Band Research Articles

Determination of the band gap and the split-off band in wurtzite GaAs using Raman and photoluminescence excitation spectroscopy

GaAs nanowires with 100% wurtzite structure are synthesized by the vapor-liquid-solid method in a molecular beam epitaxy system, using gold as a catalyst. We use resonant Raman spectroscopy and photoluminescence to determine the position of the crystal-field split-off band of hexagonal wurtzite GaAs. The temperature dependence of this transition enables us to extract the value at 0 K, which is 1.982 eV. Our photoluminescence excitation spectroscopy measurements are consistent with a band gap of wurtzite GaAs below 1.523 eV.

Hole spin surfaces in wurtzite semiconductors

Spin properties of holes in the wurtzite semiconductors, when the hole with a given wave vector ballistically propagates in either heavy-, light-mass or crystal-field split-off band, are considered. Analytical solutions for an averaged hole spin are found for two important cases, when the hole wave vector is parallel and perpendicular to the hexagonal axis. Shapes of the spin surfaces are presented for these cases. It is shown that the surfaces, in general, are spheroids. However, depending on the wave vector magnitude and valence band parameters, the surfaces may also be spheres or line-shaped. The properties of the spin surfaces are illustrated for parameters of the wurtzite GaN, where the crystal field dominates in the splitting of the valence band.

Theory of reflectance-difference spectroscopy in ordered III-V semiconductor alloys.

Spontaneous CuPt-like ordering in III-V alloys causes an anisotropy in the intensities of the transitions between the split valence-band maximum states and the conduction-band minimum. This optical anisotropy has been detected in ordered III-V alloys using modulated reflectivity, and more recently, using reflectance-difference spectroscopy (RDS). We derive here a general formula relating the ordering-induced bulk RDS intensity with the degree of long-range order. We show that the previously neglected coupling between the spin-orbit split-off band and the crystal-field split-off band is crucial for determining the RDS intensity of the ${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$P alloy.