THIN-FILM PHOTODETECTORS GROWN EPITAXIALLY ON SILICON

Epitaxial germanium films of thickness d almost-equal-to 4 mum, grown on silicon (001) by a low-temperature MBE process, constituted the base material of a silicon-integrated infrared detector. Characterization of the fully relaxed films was performed mainly by ex situ techniques, such as X-ray diffraction, Rutherford backscattering spectrometry and channeling, room temperature Hall effect and defect etching. Mesa diodes, fabricated from the originally p-type Ge films after pn-junction formation by thermal diffusion of antimony (Sb), showed quantum yields above 40% at wavelengths between 1200 nm and 1500 nm without an antireflection coating. The rise time of the photodiode signal in response to a picosecond laser pulse (tau = 300 ps) at a wavelength of 1300 nm was 530 ps. Forward current-voltage characteristics of the devices were described by an ideality factor n = 1.25, while excess current under reverse bias was attributed to leakage caused by threading dislocations in the active layers.