Amorphous germanium layers prepared by UV-photo-induced chemical vapour deposition

Hydrogenated amorphous germanium (a-Ge:H) films have been deposited via laser induced chemical vapour deposition (LCVD) by irradiating germane/helium mixtures with an ArF excimer laser beam passing parallel above Si(100) wafers, metal plates and glass substrates. The analysis of the film thicknesses by profilometry and the characterisation of the material properties by scratch testing, FTIR spectroscopy, Raman spectroscopy, and hydrogen effusion measurements, showed significant dependencies of the growth rate and of the material properties on various processing parameters such as laser power, total pressure, and substrate temperature. Very homogeneous, adherent, and low impurity a-Ge:H films with thicknesses from 10 to 100 nm have been obtained at laser power around 1 W, total pressure of 40 Torr and substrate temperature of 250°C. Higher laser power, total pressure and especially the enhancement of the substrate temperature above the threshold for the thermally induced deposition process lead to higher growth rates but also to the formation of less adherent films and powdery deposits with microcrystalline components.