Photoluminescence excitation spectroscopy of the dense exciton gas involved in the lasing transition in ZnSe epitaxial layers

The lasing transition in ZnSe epitaxial layers has been investigated at 77 K. The lowest lasing threshold (I/sub th/) was achieved when the layers were resonantly excited at the photon energy of the exciton level. It was found that the exciton level at the excitation intensity just above the I/sub th/ was red-shifted by about 16 meV compared with the free exciton line (2.792 eV) under weak excitation condition. The energy difference between the exciton line and the lasing peak was about 19 meV at I=I/sub th/ and increased with increasing excitation intensity up to I=8/spl times/I/sub th/. This suggests that the stimulated emission occurs due to the inelastic exciton-exciton scattering process at this temperature.<
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