Magnetophonon Effect of Hot Electrons in n-InSb and n-GaAs

Abstract

The effect of electric field on the magnetophonon structure has been investigated by several workers in n-InSb at 77K with main emphasis on the mechanisms of the shift of the resonance extrema to higher magnetic fields with increasing electric field in the transverse configuration [1–3]. Four mechanisms are proposed for the shift [3], which are (a) repopulation effects of hot electrons at higher Landau levels in the non-parabolic conduction band, (b) electrically distorted band structure (Stark shifted Landau structure), (c) intra-collisional field effects, and (d) distortion of the distribution function produced by hot-electron pile-up close to the LO-phonon emission threshold. At low temperatures (<40K) the magnetophonon oscillations found at weak electric fields disappear as soon as ionized impurity scattering becomes dominant relaxation of the electrons. At a moderately strong electric field magnetophonon oscillations reappear with complex series of peaks at the low temperatures. The reappearance is thought of as arising from an oscillatory variation of the energy relaxation time with magnetic field [4]. These magnetophonon series are identified as arising from a process whereby an electron falls from a Landau level into a bound state of a shallow donor involving an LO phonon emission (impurity series) and arising from the inter-Landau level transition accompanied by the emission of pairs of TA phonons at the zone boundary (X point) (2TA series) [4,5]. Additional series called magneto-impurity resonance are also observed which involve the interaction between a free carrier and a neutral impurity in a magnetic field [6]. Amplitudes of the two series, the impurity and 2TA series, reflect electron population at higher Landau levels and thus the Fourier amplitudes of the two series depend on the applied electric field [7]. These observations predict a possibility to deduce mean temperature of hot electrons [7]. In this paper we report a detailed investigation of the electric field effects on the damping factor in the transverse magnetoresistance at 77K and also an estimation of the hot-electron temperature as a function of applied electric field in the longitudinal magnetic fields at a low temperature (15.5K in GaAs). The samples used are n-GaAswith n = 3.3X10¹³ cm^-3 and μ = 1.74X105 cm²/V⋅s and n-InSb with n = 3.0X10¹³ cm^-3 and μ = 4.6X10⁵ cm2/V·s at 77K.