Auger decay of excitons in Cu2O

The nonradiative recombination of an exciton due to a collision with anothe r exciton (i.e., Auger recombination) is the dominant loss mechanism for ex citons at high densities in photoexcited Cu2O. The principal evidence is th at (a) the observed lifetime of excitons shortens substantially at high den sities, and (b) the exciton density increases sublinearly with increasing e xcitation power. To achieve exciton densities at which this two-body decay process comes into play, the particles are produced within a few micrometer s of the crystal surface using intense pulsed excitation with photon energi es well above the semiconductor band gap. In the past, determination of the "Auger constant" A in the two-body decay rate, 1/tau = An, was limited by insufficient knowledge of the exciton density n. In the present work, we ha ve determined the density of excitons by (a) measuring their absolute brigh tness in a calibrated optical system and (b) measuring the expanding volume occupied by the excitons. The luminescence signal following subnanosecond laser excitation exhibits a decay rate which is strongly dependent on the p article density. While some modeling is required to determine the volumes a t earliest times, we believe that we have determined the Auger constant to within a factor of 2. The experimental value, A = 7 X 10(-17) cm(3)/ns, is nearly two orders of magnitude larger than that derived from spectroscopic analysis. Such a strong Anger decay prevents the gas from achieving average densities in the quantum statistical regime of an ideal gas. [S0163-1829(9 9)13239-9].