Размерные эффекты в тонких пленках GeTe

Abstract

Dependences of electric conductivity σ, the Seebeck coefficient S, the Hall coefficient RH, charge carrier mobility μн and thermoelectric power P = S2σ on the thickness d (d = 5-210 nm) of GeTe thin films grown by thermal evaporation in vacuum of GeTe crystals with subsequent condensation on (001) KCl substrates at temperature TS = 520 K have been studied. For films of different thickness the temperature dependences of σ, Rн and μн in the range of 80-300 K have been obtained and power coefficient ν in the dependence μн(Т) has been determined. Electron microscopy and electron diffraction methods have been used to show that the films possess a rhombohedral structure corresponding to a low-temperature α-modification of GeTe and grow with the preferred orientation (111) and (111) (111) || (001) KСl. It has been established that with a growth of film thickness to ~ 100-150 nm, the values of σ, μн and ν are monotonously increased, the dependences Rн(d), S(d) and P(d) have the form of curves with a peak at ~ 75 nm, and with further increase of d the kinetic coefficients are practically unvaried. The dependence of properties on the thickness of films testifies to manifestation in GeTe films of classical size effect. Theoretical calculation of the dependence σ(d) made in the framework of the Fuchs-Sondheimer theory is in good agreement with the experimental data. It has been established that the concentrations of holes in the films are lower, and S and P values are higher than in the bulk crystal. Maximum Р values are achieved at d ~ 75 nm.