Amorphous-to-crystalline transformation of SiGe films and their structural-optical properties

Most of the advances in the current microelectronics industry derive from the experimental work involving semiconductor materials in the form of films (functioning as transistors, waveguides, sensors, etc.). The whole process considered various classes of materials (IV-IV-, III-V- and II-VI-based semiconductors) and it became possible only after their production and properties-control have been achieved. The same reasoning applies to the SiGe films in which new-intermediate (between those of Si and Ge) electronic-optical properties are expected to be mastered. Besides the Si-to-Ge relative composition, the final properties of the SiGe films are also susceptible to their atomic structure that, depending on the production-processing methods, can be amorphous, (nano-, micro-)crystalline, or a mixture of both. Motivated by these facts, the amorphous-to-crystalline transformation of Si 1-x Ge x (with x ranging from 0 to 1) films was considered in detail in this work. The films were prepared by a standard (plasma-assisted) method and their main properties were investigated as a function of the Ge-to-Si relative composition and as influenced by different temperatures (of anneal and measurement). Raman scattering provided the structural information of the films, like the temperature at which the amorphous-to-crystalline transformation takes place as well as particulars of the lattice dynamics in the ∼ 80–1000 K range. Likewise, temperature-dependent optical transmission measurements yield the bandgap E gap of the amorphous-crystalline films, along with their E gap (T) behavior. Finally, the main aspects relating the composition, annealing-measurement conditions and structural-optical properties of the Si 1-x Ge x films are presented and discussed envisaging future applications.