GaSb band-structure models for electron density determinations from Raman measurements
Maicol Ochoa, James E. Maslar, Herbert S. Bennett
We investigate the use of Raman spectroscopy to measure carrier concentrations in n-type GaSb epilayers with the goal of aiding in the development of this technique for 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 G and L minima. Furthermore, we evaluate three conduction band models: 1) both minima parabolic and isotropic; 2) the G minimum non-parabolic and isotropic and the L minima parabolic and isotropic; and 3) the G 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 model with the ellipsoidal L minima compared to the other two models. Direct comparison of the carrier concentrations from the Raman spectral measurements to those from the Hall effect measurements is difficult due to the GaSb conduction band structure. To evaluate the conduction band models, we calculated the L to G 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 least at room temperature and for higher doping levels. This observation could have implications not only for Raman spectral modeling but also for any investigation involving the GaSb conduction band, e.g., modeling electrical measurements or calculating electron mobility.
, Maslar, J.
and Bennett, H.
GaSb band-structure models for electron density determinations from Raman measurements, Journal of Applied Physics, [online], https://doi.org/10.1063/5.0140357, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=935525
(Accessed June 6, 2023)