Role of the Electron-Hole Interaction on Femtosecond Hole Relaxation in InP

Abstract

Investigations of carrier relaxation in optically excited polar semiconductors are often frustrated by the inability to separate electron and hole relaxation processes. In general, photo-luminescence experiments measure the product of electron (f e ) and hole (f h ) occupation functions, whereas absorption saturation experiments measure their sum. Since holes relax much faster than electrons due to a stronger lattice-coupling and larger effective mass, e-h plasma dynamics are often dominated by electron dynamics. As a result, hole-relaxation mechanisms are less well understood than those involved in electron relaxation. Doped semiconductors have been used to provide initial conditions that isolate the minority-carrier dynamics. In particular, Zhou et al 1 observed hole relaxation in n-GaAs and n-InP by time-resolved luminescence. With excitation at 2.0 eV, the relaxation time was determined to be 400 fsec for n-InP and independent of doping density in the range 5 x 1017 to 2.5 x 1018 cm -3. The dominant hole-relaxation mechanism was identified as deformation-potential coupling to optical phonons. However, electrons are degenerate in these doped materials and, therefore, hole relaxation via electron-hole scattering is impeded2. We report on experiments performed in intrinsic InP with non-degenerate plasmas that are sensitive to hole relaxation via energy transfer from hot holes to low-energy electrons.