Epitaxial Sc1−xTixN(001): Optical and electronic transport properties

Abstract

Single crystalline Sc1−xTixN layers, with compositions spanning the entire range (0⩽x⩽1), were grown on MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition at 750 °C. Optical transmission and reflectivity spectra are well described by a Drude–Lorentz model. The optical carrier density N* increases linearly from 1.0×1021 for ScN to 4.6×1022 cm−3 for TiN while the room-temperature electrical resistivity ρ300K varies by more than 2 orders of magnitude, from 2×10−3 Ω cm for ScN to 13 μΩ cm for TiN. ρ300K agrees well with optically determined resistivity values for alloys with compositions up to x=0.66, corresponding to the onset of electron filling in the second and third conduction bands. We calculated ScN and TiN band structures by ab initio density functional methods and used the results to simulate the field responses of free carriers in the Sc1−xTixN layers. From this, we determined, in combination with the measured temperature dependence of the resistivity, the low-temperature carrier relaxation time τ(x). The composition dependence of τ is dominated by alloy scattering and agrees well with our measured optical results. Hall experiments were used to obtain the effective carrier density Neff(x) which increases linearly with x up to x=0.4. Neff(x) is relatively flat for alloy compositions between x=0.4 and 0.7, due to anisotropies in the conduction band, and exhibits a steep increase at x>0.7 as higher lying conduction bands begin to be occupied. Our simulated Sc1−xTixN electronic transport properties are in good agreement with experiment. Interband optical absorption results can also be understood based upon the calculated band structures.