Polarised hot electron luminescence in p-GaAs: Electric field effects

Abstract

Electrons photo-excited to high-energy conduction band states of GaAs exhibit complex energy and momentum distributions determined by the anisotropic valence band structure and the optical matrix elements. In p-type GaAs a fraction of these hot electrons combine with localised acceptor states, producing a hot electron luminescence (HEL) spectrum with a cascade of peaks corresponding to discrete energy losses resulting from LO-phonon emission. The highest peak involves unscattered electrons, and their energy distribution is due to warping of the initial heavy-hole (HH) bands. We report measurements of the line shape of this 0-HH peak, and its polarisation profile which identifies emission from electrons along particular directions. An applied electric field of 1 kV cm −1 distorts the hot electron momentum distribution, and this is reflected in the polarisation profile. These line shapes and profiles, with and without field, are calculated using a computer model incorporating a k·p band structure and optical matrix elements, the effect of electric field being included using a k -broadening model. The data and model are in good quantitative agreement assuming an electron lifetime of ∼100 fs, and confirm the expected differences in the profiles for different excitation polarisation states and applied field directions.