Minority carrier lifetimes in germanium on silicon heterostructures

Photodiodes sensitive in the NIR and integratable with Si have been pursued for many applications including imaging, communications, and photovoltaics. Since the Si bandgap is inefficiently matched to NIR wavelengths, photodiodes fabricated from a smaller bandgap material are needed. 25 nm crystalline Ge on Si using HDP-CVD and various RTA temperatures were characterized and compared to directly deposited poly- Ge and epi-Ge. TEM showed that recrystallization using RTAs below the Ge melting point and liquid phase epitaxy using RTAs above the Ge melting point resulted in recrystallized poly-Ge with varying degrees of defects. Epi-Ge resulted in the highest level of coherent crystallinity. Inductively-coupled photoconductance measured effective lifetimes for all structures ranged from 2x103 - 2x104 cm/s. Thicker directly deposited epi-Ge samples indicated that recombination at the Ge-Si interface dominated the effective lifetime. Hydrogen passivation stability of Si and Ge surfaces in air were also characterized using electron-hole recombination lifetimes