Raman scattering reveals strong LO-phonon-hole-plasmon coupling in nominally undoped GaAsBi: optical determination of carrier concentration

Abstract

Abstract:We report room-temperature Raman scattering studies of nominally undoped (100) GaAs 1−x Bi x epitaxial layers exhibiting Biinduced (p-type) longitudinal-optical-plasmon-coupled (LOPC) modes for 0.018 ≤ x ≤ 0.048. Redshifts in the GaAs-like optical modes due to alloying are evaluated and are paralleled by strong damping of the LOPC. The relative integrated Raman intensities of LO(Γ) and LOPC A LO /A LOPC are characteristic of heavily doped p-GaAs, with a remarkable near total screening of the LO(Γ) phonon (A LO /A LOPC → 0) for larger Bi concentrations. A method of spectral analysis is set out which yields estimates of hole concentrations in excess of 5 × 10 17 cm −3 and correlates with the Bi molar fraction. These findings are in general agreement with recent electrical transport measurements performed on the alloy, and while the absolute size of the hole concentrations differ, likely origins for the discrepancy are discussed. We conclude that the damped LO-phonon-hole-plasmon coupling phenomena plays a dominant role in Raman scattering from unpassivated nominally undoped GaAsBi.

GaAs1−yBiy Raman signatures: illuminating relationships between the electrical and optical properties of GaAs1−yBiy and Bi incorporation

“…10 However, as indicated by Steele, these concentrations are higher than those measured by Pettinari et al Hall measurement was performed on these samples. However, the resistance was higher than the system limit and no signal could be captured.…”

“…A. Steele et al,10 showed that the relative intensity of the Bi-induced longitudinal-opticalplasmon-coupled (LOPC) mode to the GaAs longitudinal-optical (LO) phonon (Γ) is positively related to hole concentration, as shown earlier in numerous earlier studies of doped GaAs.…”

“…16 Typical GaAs 1−y Bi y Raman spectra can be found in two prior studies. 9,10 Four polarized quasi-backscattering geometries can be used for the GaAs zinc blende structure:…”

“…In general, the I LOPC /I LO ratio is positively correlated to carrier concentration in GaAs. 10 M. Seon et al studied the relationship between the GaAs I LOPC /I LO and doping density. 15 Steele's work extended this analysis to GaAs 1−y Bi y wherein the relative intensity ratio is an indication of the hole concentration and, therefore, the acceptor nature of Bi.…”

Photoinduced tunability of the reststrahlen band in4H−SiC

“…As N is increased, ! (near the LO phonon frequency for low N) is driven to higher frequencies as it approaches the avoided crossing (defined by the plasma frequency), forcing significant changes in reflectance [28]. Harima et al demonstrated this effect statically using Raman scattering of SiC epitaxial layers with different ionized dopant levels [13,19], while others have used modified graphene overlaid on SiC to statically tune the permittivity [29,30].…”