Growth and characterization of undoped ZnO films for single crystal based device use by radical source molecular beam epitaxy (RS-MBE)

The integrated use of(1 1 (2) over bar 0) a-plane sapphire substrates and h igh temperature growth with low temperature buffer layers have led to high quality undoped ZnO epitaxial films with mobilities as high as 120 cm(2)V(- 1) s(-1) and residual carrier concentrations as low as 7.6 x 10(16) cm(-3). Pole figure measurements reveal that a-plane sapphire substrates are effec tive for the elimination of 30 degrees rotation domains, which usually appe ar using c-plane sapphire substrates. In particular, when using c-plane sap phire substrates annealing at 1000 degreesC in O-2 with c/2-height surface steps, the X-ray diffraction pole figure peak intensity related to these re lation domains increased. The use of low temperature buffer layers allow hi gh temperature Zn0 growth on sapphire, as initial ZnO growth does not occur at high initial growth temperature. (C) 2001 Elsevier Science B.V. All rig hts reserved.