Abstract
We have investigated the intense infrared photoluminescence (PL) from several dozen molecular-beam-epitaxy Si1-xGex layer samples. For one sample the PL was imaged with an infrared camera with the emission integrated from 650 to 1000 meV. This sample was a SiGe/Si multiple quantum well (MQW) structure, with 40 Si0.7Ge0.3 layers 7.6 nm thick separated by 20 nm of Si on a Si(001) substrate. For excitation at normal incidence, the PL was brightest at the excitation point, but similarly intense at the sample edge. With focused excitation, the edge emission spot had the same diameter as the emission at the excitation spot. Thus the emission was much more collimated in the MQW waveguide than normally in bulk luminescence. Analysis of the luminescence spectral linewidth was performed to estimate the lateral dimensions of the Ge nanocrystals, values which were compared with plan-view TEM results.
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