Many types of nanocrystals are under investigation for variety of applications ranging from optics to sensing. In our group, Si, Ge and SiGe nanocrystals in oxide and nitride matrices are being investigated for memory and solar cell applications. Plasma enhanced chemical vapor deposition is used to deposit oxide or nitride layers rich in the element intended for nanocrystal formation. High temperature furnace treatment as well as rapid thermal annealing is used to precipitate defect free nanocyrstals. Such materials are studied with transmission electron microscopy, Raman scattering, atomic force microscopy.
In a recent collaborative work with HZDR-Dresden and METU, we are now studying the formation of nanocrystal networks using high power lasers for applications in solar cells. Using the well known band gap widening of c-Si at the nanoscale, we aim to form networks of Si nanocrystals in initially Si rich thin SiO2 layers. Kinetic Monte Carlo and high temperature furnace annealing data suggest that laser induced spinodal decomposition can be expected to lead to phase separation of these films. Such sponge like Si nanocrystal networks are expected to down convert solar radiation and lead to high efficiency solar cells in tandem with current a-Si cells.