Abstract

The initial relaxation process of hot photoinjected carriers in bulk GaAs is dominated by optical phonon emission at low carrier densities (10¹⁷ cm^-3). The emitted phonons exist as a nonthermal phonon population until they decay anharmonically. Previously, the generation and decay of non-thermal phonons was studied using time resolved anti-Stokes raman spectroscopy.^[1] For carrier densities larger than 10¹⁷ cm^-3 coupling of the carrier plasma to the optical phonons in a polar material becomes non-negligible. In GaAs plasmon-phonon coupled modes have been observed in both single component plasmas (via doping)^[2] and two component plasmas (via optical excitation).^[3] Due to the interaction of the phonons with the carrier plasma there have been no measurements of the phonon population dynamics under high excitation conditions. However, these non-equilibrium phonons play an important role in theories of hot carrier relaxation at high densities. In particular the existence of a large non-thermal phonon population and its reabsorption by carriers has been used to explain a reduction in the carrier energy loss rate.^[4]

© 1992 IQEC