Temperature dependence of semiconducting and structural properties of Cr-Si thin films

Electrical and structural properties of coevaporated Cr-Si thin alloy films and bilayer Cr/Si films as a function of annealing temperature from 10 to 1000°K have been studied by in situ electrical resistivity and Hall measurements, and structural analysis including MeV ⁴He⁺ ion backscattering, x-ray diffraction, Auger electron spectroscopy combined with Ar sputtering, electron microprobe, and scanning and transmission electron microscopy. In the as-deposited state, the coevaporated alloy film was amorphous. Upon annealing, a sharp increase in resistivity occurred near 270°C and the increase has been determined to be amorphous to crystalline CrSi₂ phase transformation. The resistivity increased further with annealing up to 550°C then a gradual decrease took place beyond 600°C. In cooling, the resistivity increased monotonically with decreasing temperature. For the bilayer Cr/Si films, the annealing behavior is similar except the sharp increase in resistivity occurred around 450°C due to the formation of CrSi₂. The crystalline CrSi₂ has been determined to be a semiconductor with an energy gap of 0.27 eV. It is p-type, having a hole concentration of 4×10¹⁹ cm^-3 at room temperature and a hole mobility of 7.2×10⁴×T (temp)^-3/2 cm²/V sec in the acoustic scattering region. The kinetics of amorphous-to-crystalline transformation of Cr-Si alloy film in the temperature range of 225-25°C has been determined to follow a t⁷ (time) dependence with an apparent activation energy of 1.13 eV.