Thin films of a-SiGe:H with device quality properties prepared by a novel hollow cathode deposition technique

Using a novel hollow cathode plasma-jet reactive sputtering system in which an intense plasma, ignited in an Ar/H2 flow, is directed through silicon and germanium nozzles, a series of a-SiGe:H thin films have been prepared on silicon and on glass substrates. These films have been optically characterized by infrared (IR) spectroscopy, surface Raman spectroscopy and spectroscopic ellipsometry (335-1000 nm). Total hydrogen concentrations, as determined by FTIR, varied with deposition conditions and ranged from 2.5×1021 to 1.6×1022 atom cm−3 and correlated with secondary ion mass spectrometry (SIMS) elemental analyses to within 10%. The ellipsometric spectra of the films have been fitted with a modified Tauc-Lorentz model for the determination of film properties, including thickness (ranging from 400 to 1100 nm) along with film uniformity and surface roughness. Conductivity measurements in the dark and under simulated AM1 solar illumination have indicated that the films grown exhibit device-quality properties. The light-to-dark conductivity ratio has consistently been greater than 1000 for films with bandgaps down to 1.3 eV. Relationships between deposition parameters, light-and-dark conductivity properties, and chemical structural features are discussed.