Crystallization of Amorphous Germanium Films and Multilayer a-Ge/a-Si Structures upon Exposure to Nanosecond Laser Radiation

Abstract

The processes of the crystallization of amorphous germanium films and multilayer germanium/silicon structures upon exposure to nanosecond (70 ns) ruby laser radiation (λ = 694 nm) are studied. The samples are grown on silicon and glassy substrates by plasma-enhanced chemical vapor deposition. Pulsed laser annealing of the samples is conducted in the range of pulse energy densities E_p from 0.07 to 0.8 J cm^–2. The structure of the films after annealing is determined by analyzing the scanning electron microscopy data and Raman spectra. It is established that, after annealing, the films are completely crystallized and, in this case, contain regions of coarse crystalline grains (>100 nm), whose fraction increases, as E_p is increased, and reaches 40% of the area. From analysis of the position of the Raman peaks, it is conceived that the crystalline grains, whose dimensions exceed 100 nm, either contain structural defects or stretching strains. The correlation length of optical vibrations is determined from the phonon confinement model and found to increase from 5 to 8 nm, as E_p is increased. Pulsed laser annealing of multilayer Ge(10 nm)/Si(5 nm) structures induces partial intermixing of the layers with the formation of Ge–Si alloys.