Tuning of charge carriers in Bi2Te3 thin films via swift heavy ion irradiation

The irradiation-induced effects of Ni 7+ ion irradiation on the structural and electrical properties of e-beam evaporation synthesized Bi 2 Te 3 thin films have been examined. X-ray Diffraction (XRD) results revealed that the films possessed a polycrystalline rhombohedral (R-3 m) crystal structure. No appreciable change was observed in lattice parameters a = b while c varied non-monotonically indicating an anisotropic variation of the unit cell under different ion fluences. X-ray peak profile analysis indicated a slight reduction in average crystallite size and an increase in lattice strain due to irradiation. Raman spectra of the films demonstrated the effect of irradiation on A 1 u 1 modes evolved from c-axis vibrations with ion fluence. The observed decrease in surface roughness through Atomic Force Microscopy (AFM) images up to 3 × 10 12 ions/cm 2 might be due to the formation of nanocrystallites with small sizes on the surface. The composition of the as-prepared thin films was found to be near stoichiometry of Bi 2 Te 3 as revealed by X-ray Photoelectron Spectroscopy (XPS) analysis. The resistivity of films gets increased up to 3 × 10 12 ions/cm 2 as evident from the low-temperature transport measurements. The variation correlation of electrical resistivity with the Hall coefficient is examined as a function of ion fluence. The irradiation-induced crossover behavior is resulted in films with ion fluence from the n to p -type carriers. Interestingly, the bulk charge carriers are compensated with tunning of the Fermi level in ion-irradiated thin films.