RUI: Fundamental Studies of a-Ge:H and a-SiGe:H Deposition by Reactive Magnetron Sputtering

Macalester College, Saint Paul MN

Investigators

Abstract

TECHNICAL EXPLANATION: This project aims for greater understanding of the deposition of hydrogenated amorphous germanium (a-Ge:H) and hydrogenated amorphous silicon-germanium (a-SiGe:H) by direct current reactive magnetron sputtering-materials with relevance to photovoltaic applications. The approach focuses on the role of energy and momentum flux into the surface during growth in determining film properties, and the elucidation of the mechanism of hydrogen incorporation in the film. The plasma density will be systematically varied using an unbalanced magnetron and an external magnetic field; a radio frequency bias will be used to control the ion energy. Plasma characteristics will be determined using plasma probes. Monte Carlo simulations of sputter atom transport will be utilized to determine the energy, flux, and angular distribution of energetic neutral bombardment, to be verified by experimental studies of deposition profiles. Hydrogen incorporation kinetics will be studied by mass spectrometry and optical emission spectroscopy. These data will be correlated with compositional, structural, optical, and electrical properties of the resulting films as determined by optical transmission and reflection spectroscopy, infrared absorption spectroscopy, Rutherford Back Scattering, Elastic Recoil Detection, photo and dark conductivity, and subgap absorption spectroscopy. This information will provide a sound basis for understanding the causes of the inferior properties of these materials compared to hydrogenated amorphous silicon, and should lead to further optimization of these technologically important materials. This study is expected to make an important contribution to basic understanding of thin film growth by sputter deposition.. NON-TECHNICAL EXPLANATION The project addresses fundamental materials research with strong technological relevance to electronics and photonics, and effectively integrates research and education. The research will be carried out in collaboration with undergraduate research assistants at Macalester College, a four-year liberal arts college. The project will provide valuable research training for students by providing unique research opportunities, by providing options for academic year independent research projects, and by enhancing courses related to materials science in the physics curriculum. It will also serve as a model for materials research at an undergraduate institution, and as a model for the integration of research and teaching in a liberal arts college physics department.