Influence of hydrogen on structural and optical properties of low temperature polycrystalline Ge films deposited by RF magnetron sputtering

• Published in: Journal of crystal growth 2010-09, Vol.312 (19), p.2647-2655
• Main Authors: Tsao, Chao-Yang, Campbell, Patrick, Song, Dengyuan, Green, Martin A.
• Format: Article
• Language: English
• Subjects: A1. Characterization; A1. X-ray diffraction; A3. Physical vapor deposition processes; Applied sciences; B1. Germanium; B3. Solar cells; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Deposition; Deposition by sputtering; Diffraction; Energy; Energy gaps (solid state); Exact sciences and technology; Germanium; Glass; Hydrogen storage; Magnetron sputtering; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Natural energy; Optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Photovoltaic conversion; Physics; Solar cells. Photoelectrochemical cells; Solar energy; Thin films
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2010.06.008

To improve the properties of polycrystalline Ge thin films, which are a candidate material for the bottom cells of low cost monolithic tandem solar cells, ∼300 nm in situ hydrogenated Ge (Ge:H) thin films were deposited on silicon nitride coated glass by radio-frequency magnetron sputtering. The films were sputtered in a mixture of 15 sccm argon and 10 sccm hydrogen at a variety of low substrate temperatures ( T s )≤450 °C. Structural and optical properties of the Ge:H thin films were measured and compared to those of non-hydrogenated Ge thin films deduced in our previous work. Raman and X-ray diffraction spectra revealed a structural evolution from amorphous to crystalline phase with increase in T s . It is found that the introduction of hydrogen gas benefits the structural properties of the polycrystalline Ge film, sputtered at 450 °C, although the onset crystallization temperature is ∼90 °C higher than in those sputtered without hydrogen. Compared with non-hydrogenated Ge thin films, hydrogen incorporated in the films leads to broadened band gaps of the films sputtered at different T s .