Hall mobility and field effect mobility studies on PbTe HWE thin films

Hall mobility (μ_H) and field effect mobility (μ_FE) studies were carried out on PbTe films of different thickness grown on KCl (100) substrates by the hot wall epitaxy (HWE) technique. The Hall mobility was obtained using the standard Van der Pauw technique. The diffused scattering mobility, μ_D, due to size effect was calculated and compared with μ_H. A large discrepancy between μ_H and μ_D was explained on the basis of a residual mobility contribution which was attributed to the scattering due to grain boundaries, dislocations, cleavage steps and other surface effects. For AC field effect studies an MIS structure with a thin mica spacer between the film surface and metal electrode was used. The field effect mobility, μ_FE, was obtained at different temperatures from 98 to 156 K in the frequency range of 40 to 200 kHz. The variation of μ_FE with frequency was found to be largely due to the relaxation of fast surface states having time constants from 1.84 to 0.96 μs in the above temperature range. The activation energy and capture cross-section of these surface states were calculated to be 0.02 eV and 10⁻¹⁹ cm² respectively. Unlike the Hall mobility, the effective DC field effect mobility derived from the experimental results was found to be independent of film thickness.