Improvement of crystallinity by post-annealing and regrowth of Ge layers on Si substrates

Post-annealing and regrowth of Ge were investigated to improve the crystallinity and to control the lattice strain of Ge layers directly grown on a Si substrate by low-temperature epitaxial growth. The post-annealing at a higher temperature was an effective way of improving the surface morphology and the crystallinity of the Ge layers. Furthermore, the lattice strain changed from compressive to tensile in < 110 > crystal orientation when the post-annealing temperature was increased, and the tensile strain of 0.19% was achieved at the annealing temperature of 700 °C. Consequently, the photoluminescence (PL) intensity increased with the increasing post-annealing temperature and a red-shift of the PL spectra could be observed due to reduction of direct bandgap energy at Г-point with the tensile strain. Although regrowth of the Ge layers had little impact on the lattice strain at a relatively low regrowth temperature, a thick Ge layer with high crystallinity was formed at 700 °C and a favorable PL spectrum was obtained. These results indicate that this combined technique can improve the performance of Ge light-emitting devices.