MgxZn1-xO Films with a Low Residual Donor Concentration (< 10(15) cm(-3)) Grown by Molecular Beam Epitaxy

We have grown undoped MgxZn1-xO films on Zn-polar ZnO substrates by using a plasma-assisted molecular beam epitaxy technique. The residual donor concentration (ND) was evaluated by capacitance-voltage measurements of the Schottky junctions formed using poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) films as electrodes. Increasing the Zn/O flux ratio during the growth reduced the value of ND to reach (2-7) x 10(14) cm(-3) for MgxZn1-xO films with MgO molar fractions x ranging from 0 to 0.39. These MgxZn1-xO films with low residual ND values would be suitable host materials for p-type doping. (C) 2010 The Japan Society of Applied Physics