SixGe1−x films and heterojunctions produced by epitaxial crystallization of a-SixGe1−x alloys on GaAs

We studied the structural and electrical properties of crystallized a-SixGe1−x alloys with 0⩽x⩽1 on (1 0 0) GaAs substrates. Raman spectroscopy on laser crystallized films shows the Si–Si, Ge–Ge, and Si–Ge vibrations characteristic of crystalline SixGe1−x alloys. The Raman polarization selection rules indicate that, while SixGe1−x films with x up to 25% are epitaxial, those with higher Si concentrations are polycrystalline with oriented grains. Heterojunctions formed by crystallizing a-Ge films on p-type GaAs exhibit Ohmic behavior. Ge/n-GaAs heterojunctions, in contrast, show rectification with current versus voltage characteristics compatible with the behavior of n–n structures. These heterojunctions are sensitive to light with wavelengths up to 1600 nm, thus demonstrating that they can be used as detectors in the spectral range for optical communications (1300–1550 nm).