Intraband inversion due to ultrashort carrier lifetimes in proton-bombarded InP

We report the evidence of occupation inversion in time average within the continuous band structure of the semiconductor InP. Ultrafast carrier trapping and recombination ({τ}{}1×{}10^-13 s) as a consequence of proton bombardment prevents the thermalization of optically excited electron-hole pairs (n{~}3×{}10¹⁶ cm^-3). Beyond previous experimental observations of inverted time-averaged luminescence spectra, we present experimental data at lower carrier concentrations, which are in quantitative agreement with ensemble Monte Carlo simulations. Inverted electron and hole energy distributions are determined quantitatively. We propose the application for a solid-state free-electron laser. {} 1996 The American Physical Society.