| Abstract | Photoluminescence has been observed from Si1−xGex alloy layers, superlattices and non-periodic multilayers where x was varied from 0 to 0.6 A p-type Si0.82Ge0.18 alloy layer 200 nm thick, grown by molecular beam epitaxy (MBE), has been fabricated into a mesa diode which operated as a light-emitting diode, emitting at 1.4 μm at temperatures up to 80 K. This diode was selected from a series of heterostructures which exhibited intense photoluminescence with internal quantum efficiencies in the range 1%–10% at low temperatures. Photoluminescence in the wavelength range 1.2–1.7 μm has been observed from thick (100–200 nm) Si1−xGex alloys and Si1−x−Si strained layer superlattices with a range of dimensions which was large compared with the unit cell; i.e. where Brillouin zone folding effects were negligible. The intense Si1−xGex alloy photoluminescence peak had a halfwidth of about 80 meV and the peak energy was found to shift consistently and predictably with the germanium fraction. Photoluminescence peak energies at 4.2 K varied from 620 to 990 meV for germanium fractions where 0.53 >x > 0.06. The photoluminescence and electroluminescence peaks were consistently about 120 meV below the established bandgap for tetragonally strained Si1−xGex. In general, Si1−xGex strained layers grown at low temperatures typical of MBE (below 500°C) exhibited low photoluminescence intensity. However, post-growth annealing in the 500–700°C temperature range enhanced luminescence efficiency by up to two orders of magnitude. A comparison is also made of the broad intense photoluminescence observed from MBE material with the weak near-band-edge spectra obtained from Si1−xGex-Si grown by low temperature chemical vapour deposition. |
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