Tensile strain, crystal quality, and surface morphology of 500 nm thick Ge films were improved after rapid thermal annealing at 900 ℃ for a short period （〈 20 s）. The films were grown on Si（001） substrates by ultra-high vacuum chemical vapor deposition. These improvements are attributed to relaxation and defect annihilation in the Ge films. However, after prolonged （〉 20 s） rapid thermal annealing, tensile strain and crystal quality degenerated. This phenomenon results from intensive Si-Ge mixing at high temperature.
Tensile-strained Ge/SiGe multiple quantum wells （MQWs） were grown on a Ge-on-Si virtual substrate using ultrahigh vacuum chemical vapor deposition on an n＋-Si （001） substrate. Direct-bandgap electroluminescence from the MQWs light emitting diode was observed at room temperature. The quantum confinement effect of the direct-bandgap transitions is in good agreement with the theoretical calculated results. The redshift mechanism of emission wavelength related to the thermal effect is discussed,
Strain-compensated Ge/Si0.15Ge0.85 multiple quantum wells were grown on an Si0.1 Ge0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition technology on an n＋-Si（001） substrate. Photoluminescence measurements were performed at room temperature, and the quantum confinement effect of the direct-bandgap transitions of a Ge quantum well was observed, which is in good agreement with the calculated results. The luminescence mechanism was discussed by recombination rate analysis and the temperature dependence of the luminescence spectrum.
