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

Single crystalline Sc1-xTixN layers, with compositions spanning the entire range (0 less than or equal to x less than or equal to 1), were grown on Mg O(001) by ultrahigh vacuum reactive magnetron sputter deposition at 750 deg reesC. Optical transmission and reflectivity spectra are well described by a Drude-Lorentz model. The optical carrier density N-* increases linearly f rom 1.0 x 10(21) for ScN to 4.6 x 10(22) cm(-3) for TiN while the room-temp erature electrical resistivity rho (300K) varies by more than 2 orders of m agnitude, from 2 x 10(-3) Omega cm for ScN to 13 mu Omega cm for TiN. rho ( 300K) agrees well with optically determined resistivity values for alloys w ith compositions up to x = 0.66, corresponding to the onset of electron fil ling in the second and third conduction bands. We calculated ScN and TiN ba nd structures by ab initio density functional methods and used the results to simulate the field responses of free carriers in the Sc1-xTixN layers. F rom this, we determined, in combination with the measured temperature depen dence of the resistivity, the low-temperature carrier relaxation time tau ( x). The composition dependence of tau is dominated by alloy scattering and agrees well with our measured optical results. Hall experiments were used t o obtain the effective carrier density N-eff(x) which increases linearly wi th x up to x = 0.4. N-eff(x) is relatively flat for alloy compositions betw een x = 0.4 and 0.7, due to anisotropies in the conduction band, and exhibi ts 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 g ood agreement with experiment. Interband optical absorption results can als o be understood based upon the calculated band structures. (C) 2001 America n Institute of Physics.