Abstract
We observe a band-to-band photoluminescence (PL) of the well layers in GaAs/AlGaAs quantum well structures (hνP=1.56 eV) under below-gap excitation (BGE) with a Nd:YAG laser (hνB=1.17 eV) at 77 K. The origin of the up-conversion luminescence was inside the epitaxially grown well layers and is different from those reported in GaAs substrates. 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 (hνA=1.96 eV) individually. The up-conversion process corresponds to the increase in the PL intensity due to the BGE in two-wavelength excited PL, which reveals the mechanism of a cascade excitation via a below-gap state in quantum wells for the first time. A rate- equation analysis explained the measured BGE density dependence of the up-conversion luminescence.
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