Influence of the substrate temperature on the structure and surface roughness of Cd0.18Sb0.64Te0.18 films

Using a radiofrequency sputtering deposition technique, ternary Cd0.18Sb0.64Te0.18 thin films have been grown on glass substrates at several substrate temperatures (50–250°C). The samples have an Sb content of about 63 at %, as measured by Auger spectroscopy. The surface roughness, the structural and the electrical properties of the films were studied as a function of substrate temperature. X-ray diffraction (XRD) measurements showed that the structure of the films changes from an amorphous phase, when deposited at lower substrate temperatures, to a mixture of two crystalline phases (CdTe and Sb) for higher substrate temperatures. Atomic force microscopy shows an increase in the surface roughness with an increase in the substrate temperature, clearly showing the formation of crystalline phases with microcrystallite sizes in good agreement with those determined from XRD measurements. The amorphous-to crystalline transition is accompanied by an abrupt increase in the room temperature electrical conductivity of the films. This increase in the conductivity as well as its temperature dependence in the range of room temperature to 150°C can be understood in terms of an electrical percolation process through the conducting Sb crystallites.