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Optical emission and absorption properties of Si1−xGex/Si superlattices grown on (100) and (110) Si substrates were investigated to determine the optimal growth conditions for these structures to be used as infrared detectors. Fully strained Si1−xGex/Si superlattices were grown by molecular beam epitaxy (MBE) and examined using low-temperature photoluminescence to identify no-phonon and phonon-replica interband transitions across the alloy band gap. Phonon-resolved emission was most intense for undoped quantum wells grown at 710 °C for both silicon orientations. Room-temperature absorption measurements were conducted on (100) and (110) Si1−xGex/Si superlattices using Fourier transform spectroscopy while varying incident electric field polarization. Strong intersubband absorption was observed at 7.8 μm from a sample composed of 15 quantum wells of 40 Å Si0.8Ge0.2 separated by 300 Å of Si grown on (100) Si by MBE at 550 °C. Valence band wells were doped with a boron concentration of 5×1019 cm−3. No intersubband transitions were observed on similar (110) Si1−xGex/Si superlattices ranging in boron dopant from 1×1019 to 8×1019 cm−3, nor from any structure grown at 710 °C. This peak was most likely masked by free-carrier absorption which dominated the spectrum.
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