UP-CONVERSION LUMINESCENCE VIA A BELOW-GAP STATE IN GAAS ALGAAS QUANTUM-WELLS/

We observe a band-to-band photoluminescence (PL) of the well layers in GaAs/AlGaAs quantum well structures (h nu(p) = 1.56 eV) under below-g ap excitation (BGE) with a Nd:YAG laser (h nu(B) = 1.17 eV) at 77 K. T he origin of the up-conversion luminescence was inside the epitaxially grown well layers and is different from those reported in GaAs substr ates. A detailed study of a two-wavelength excited PL was carried out by changing the density of both the BGE and the above-gap excitation ( AGE) by a He-Ne laser (H nu(A) = 1.96 eV) individually. The up-convers ion process corresponds to the increase in the PL intensity due to the BGE in two-wavelength excited FL, which reveals the mechanism of a ca scade excitation via a below-gap state in quantum wells for the first rime. A rate-equation analysis explained the measured BGE density depe ndence of the up-conversion luminescence. (C) 1997 Academic Press Limi ted.