RADIATIVE RECOMBINATION AT THE ALXGA1-XAS-GAAS HETEROSTRUCTURE INTERFACE BY 2-DIMENSIONAL EXCITONS

Radiative recombination from the AlxGa1-xAs-GaAs heterostructure inter face was investigated using photoluminescence and photoluminescence-ex citation spectroscopy in modulation-doped and undoped samples. This em ission is identified as H-band A, resulting from an indirect excitonli ke transition in real space. The exciton is made up of a two-dimension al electron in the interface notch and a valence-band hole in the neut ral region, having a binding energy of 1.8 meV. The H-band A exciton i s directly excited by a free exciton making a vertical transition in r eal space. H-band A may be a distortion of the vertical direct free ex citon in real space to an indirect free exciton in real space, in whic h case only one exciton is involved; or it could result from the direc t excitation of the indirect exciton in real space by the vertical exc iton through wave-function overlap, with energy and momentum being con served. In the latter case two excitons are involved. While the exact coupling mechanism between the free exciton and the H-band A exciton i s not well understood, two possibilities are suggested.