Temperature dependence of the dielectric function and the interband critical-point parameters of GaSb

GaSb band-structure models for electron density determinations from Raman measurements

We investigate the use of Raman spectroscopy to measure carrier concentrations in n-type GaSb epilayers to aid in the development of this technique for the nondestructive characterization of transport properties in doped semiconductors. The carrier concentration is quantified by modeling the measured coupled optical phonon-free carrier plasmon mode spectra. We employ the Lindhard-Mermin optical susceptibility model with contributions from carriers in the two lowest GaSb conduction-band minima, the Γ and L minima. Furthermore, we evaluate three conduction-band models: (1) both minima parabolic and isotropic, (2) the Γ minimum non-parabolic and isotropic and the L minima parabolic and isotropic, and (3) the Γ minimum non-parabolic and isotropic and the L minima parabolic and ellipsoidal. For a given epilayer, the carrier concentration determined from the spectral simulations was consistently higher for the ellipsoidal L minima model than the other two models. To evaluate the conduction-band models, we calculated the L to Γ electron mobility ratio necessary for the electron concentrations from the Raman spectral measurements to reproduce those from the Hall effect measurements. We found that the model with the ellipsoidal L minima agreed best with reported carrier-dependent mobility-ratio values. Hence, employing isotropic L minima in GaSb conduction-band models, a common assumption when describing the GaSb conduction band, likely results in an underestimation of carrier concentration at room temperature and higher doping levels. This observation could have implications for Raman spectral modeling and any investigation involving the GaSb conduction band, e.g., modeling electrical measurements or calculating electron mobility.

Parameterized optical properties of InxAl1-xP alloys

We report values of parametric-model (PM) parameters that can be used to obtain dielectric functions (refractive indices) from 1.5 to 6.0 eV for ${{\rm In}_x}{{\rm Al}_{1 - x}}{\rm P}$In_xAl_1-xP alloys of arbitrary compositions $x$x. Using reported pseudo-dielectric data for several In compositions, we extract their dielectric functions by multilayer calculations, then parameterize them with PM lineshapes that well describe the asymmetric nature of their critical point (CP) contributions. We follow the ${E_0}$E₀ fundamental bandgap as a function of $x$x, and determine the composition of the indirect-to-direct crossover.

ab initio Energetics and Thermoelectric Profiles of Gallium Pnictide Polytypes

The state-of-the-art Density Functional Theory (DFT) is utilized to investigate the structural, electronic, vibrational, thermal and thermoelectric properties of gallium pnictides GaX (X = P, As, Sb) in cubic zincblende (ZB) and hexagonal wurtzite (WZ) phases. The lattice parameters, bulk modulus, energy band nature and bandgap values, phonon, thermal and thermoelectric properties are revisited for ZB phase while for WZ phase they are predictive. Our results agree reasonably well with the experimental and theoretical data wherever they are available. The phonon dispersion curves are computed to validate the dynamic stability of these two polytypes and for further investigating the thermal and thermoelectric properties. Our computed thermoelectric figure of merit ZT gives consistent results with highest observed magnitude of 0.72 and 0.56 for GaSb compound in ZB and WZ phases respectively. The first time calculated temperature variation of lattice thermal conductivity for WZ phase shows lower value than ZB phase and hence an important factor to enhance the figure of merit of considered gallium pnictides in WZ phase. Present results validate the importance of GaX in high temperature thermoelectric applications as the figure of merit ZT shows enhancement with significant reduction in thermal conductivity at higher temperature values.