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 MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition at 750 degreesC. Optical transmission and reflectivity spectra are well described by a Drude-Lorentz model. The optical carrier density N-* increases linearly from 1.0 x 10(21) for ScN to 4.6 x 10(22) cm(-3) for TiN while the room-temperature electrical resistivity rho (300K) varies by more than 2 orders of magnitude, 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 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 tau (x). The composition dependence of tau is dominated by alloy scattering and agrees well with our measured optical results. Hall experiments were used to obtain the effective carrier density N-eff(x) which increases linearly with x up to x = 0.4. N-eff(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. (C) 2001 American Institute of Physics.