OBSERVATION OF HIGHER SUBBAND EMISSION FROM PBSE 2-DIMENSIONAL LAYERS

Energy relaxation of an optically excited two-dimensional electron-hol e gas has been investigated in PbSe as an example for dimensional quan tization in a semiconductor with nearly symmetric valence and conducti on band extrema. As compared with bulk-like reference samples the inte rband emission exhibits broadening and splitting into up to 5 clearly resolved lines, A systematic variation of the spectra with excitation density was observed: With increasing pump intensity the width of the total spectrum and the number of subbands increase due to both carrier heating and band filling, The emission bands are attributed to transi tions between conduction and valence subbands with equal quantum numbe r, Above a threshold well pronounced for each subband transition, the emission becomes stimulated. That indicates a potential for laser appl ications.