A multi-valley model for hot free-electron nonlinearities at 10.6 mu m in highly doped n-GaAs

When the frequency of infrared light and the plasma frequency of highly dop ed n-GaAs are in resonance (e.g. for a doping concentration N = 7 x 10(18) cm(-3) and a wavelength lambda = 10.6 mum), the free-electron induced optic al nonlinearity is soundly pronounced. At such high doping concentrations i t is necessary to extend the rigid quantum mechanical description of the fr ee-electron induced nonlinearity to a multi-valley model. The central valle y of GaAs was treated as a fully nonparabolic degenerated electron gas, whe reas the satellite valley was modeled as an anisotropic electron gas of arb itrary degeneracy. The following intra- and intervalley absorption mechanis ms were taken into account: impurity assisted, thermal and hot polar optica l phonon assisted intravalley absorption on one hand and intervalley phonon assisted absorption in equivalent and nonequivalent intervalley absorption on the other hand. The dependence of the different absorption and energy r elaxation mechanisms on the doping concentration, free electron heating, op tical power density and the equivalent LL-intervalley deformation potential are discussed. We demonstrated for the first time that the behavior of the optical intervalley nonlinearity, i.e. the nonlinear absorption and nonlin ear intervalley transfer, strongly depend on the equivalent LL-intervalley deformation potential. In the linear regime the model calculations are in g ood agreement with experimental results.