Electrical properties related to the structure of GeSi nanostructured films

GeSi nanostructured films were obtained by cosputtering from two Ge and Si targets and subsequent annealing in furnace in N2 for 5 h at 700, 800 and 900 °C, with the aim to show the correlation between electrical properties and crystalline structure of the films. The as-deposited films are amorphous, have a Ge:Si composition of 55:45 and 185 nm thickness. The film structure was investigated by XRD and TEM, and the electrical behaviour was studied by measuring current–voltage (I–V) and current–temperature (I–T) characteristics and by discussing them in correlation with the structure. Different electrical behaviours of GeSi films corresponding to different structures have been evidenced. The 700 °C annealed GeSi films are formed of nanocrystals (7–15 nm) separated by amorphous regions (1–2 nm). These films present a superlinear I–V characteristic typical of high field-assisted tunnelling through potential barriers (amorphous regions) between nanocrystals. The I–T characteristic at low temperature follows a T−1/2 law showing a thermally activated tunnelling of carriers between neighboring GeSi nanocrystals. The films annealed at 800 and 900 °C have a like behavior, they are completely crystallized and present linear I–V and Arrhenius I–T dependences reflecting the polycrystalline behaviour.