Microstructure and electronic properties of the refractory semiconductor ScN grown on Mg0(001) by ultra-high-vacuum reactive magnetron sputter deposition

ScN layers, 180 nm thick, were grown on MgO(001) substrates at 750 degrees C by ultra-high-vacuum reactive magnetron sputter deposition in pure N-2 discharges. N/Sc ratios, determined by Rutherford backscattering spectroscopy, were 0.98 +/- 0.02, X-ray diffraction theta-2 theta scans and pole figures combined with plan-view and cross-sectional transmission electron microscopy showed that the films are strongly textured, both in plane and along the growth direction, and have a columnar microstructure with an average column width near the film surface of 30 +/- 5 nm. During nucleation and the early stages of film growth, the layers consist of approximately equal volume fractions of 002- and Ill-oriented grains. However, preferred orientation evolves toward a purely ill texture within similar or equal to 40 nm as the 002 grains grow out of existence in a kinetically limited competitive growth mode. 002 grains exhibit local cube-on-cube epitaxy with an orientation relationship (001)(ScN)\\(001)(Mgo) and [010](ScN)\\[010](Mgo) while 111 grains have a complex fourfold 90 degrees-rotated in-plane preferred orientation in which strained ScN triangular (111) surface unit cells exhibit local epitaxy with square MgO unit cells yielding the orientation relationship (111)(ScN)\\(001)(Mgo), [1 (1) over bar 0](ScN)\\[1 (1) over bar 0](Mgo), and [11 (2) over bar](ScN)\\[110](Mgo). Room-temperature electrical resistivity p is 1.2 x 10(4) mu Omega cm while dp/dT was found to be negative, indicating semiconducting behavior, with p varying from 1.6 x 10(4) mu Omega cm at 80 K to 1,1 x 10(4) mu Omega cm at 400 K. Optical absorption coefficients ranged from 1 x 10(4) cm(-1) at 1.5 eV to 2.6 x 10(5) cm(-1) at 3.5 eV with a well-define edge corresponding to a direct transition at 2.37 +/- 0.05 eV. (C) 1998 American Vacuum Society. [S0734-2101(98)07704-5].