STRONG ROOM-TEMPERATURE EXCITONIC RESONANCE IN CDTE-I

We report the first room temperature photoluminescence excitation stud y of iodine doped CdTe grown by metalorganic molecular beam epitaxy. T his study was motivated by the observation of strongly enhanced band e dge photoluminescence intensities, by factors of 10(2)-10(3) compared to reference samples, and by the observation of a narrow spectral line width of only 37 meV due to exciton recombination. Analysis of the pho toluminescence lineshape using Toyozawa's theory suggests a significan t excitonic contribution to the radiative recombination in these mater ials, even though the free exciton binding energy in CdTe is approxima tely 1/3 kT at 300 K. Photoluminescence excitation measurements perfor med at 300 K have revealed separated and well-pronounced excitonic res onances associated with the ground and first excited states of the fre e exciton for samples with electron concentrations < 10(17) cm(-3). At lower temperatures resonances were observed for samples doped up to 1 0(18) cm(-3). The observation of free excitons at temperatures up to 3 00 K is attributed to the high quality of the CdTe:I layers and the ab sence of mid-bandgap and ionized impurity scattering centers.