Nanostructure and infrared photoluminescence of nanocrystalline Ge formed by reduction of Si0.75Ge0.25O2/Si0.75Ge0.25 using various H2 pressures

Nanocrystalline Ge in SiO2 was synthesized by the reduction of Si0.75Ge0.25O2 with H-2, at various annealing temperatures (ranging from 700 to 900 degreesC), with various H-2 partial pressures (100% N-2, 6% H-2:94% N-2, and 100% H-2), and for a range of times. Cross-sectional transmission electron microscopy (XTEM) reveals a strong dependence of nanocrystal distribution and structure on annealing temperature and H-2 partial pressure. The oxide/semiconductor interface served as a seed layer for the growth of large Ge crystallites, whereas nanocrystals formed in the bulk of the oxide for high H-2 partial pressures or low temperatures. The mechanisms involved in nanocrystal formation are discussed in the context of XTEM and Raman spectroscopy results. Select nanocrystalline Ge samples were characterized optically with infrared photoluminescence (PL) measurements at 4 K, using a 488 nm Ar laser excitation. Nanocrystalline Ge samples with small nanocrystals (<15 nm) exhibited a broad infrared PL background ranging from about 1.0-1.7 mum. The broad background is attributed to quantum confinement in the Ge nanocrystals, consistent with a wide distribution of nanocrystal sizes and hence a broad range of confinement energies. (C) 2003 American Institute of Physics.