Two-step MBE growth of ZnO layers on electron beam exposed (111)CaF2

ZnO films are grown on(1 1 1)CaF2 by RF-plasma assisted two-step MBE. Low-temperature ZnO buffer layers with thickness below 10 nm are deposited on (1 1 1)CaF2 surfaces below 300 degrees C. The initial growth of ZnO overlayers at high temperatures on the low-temperature buffer layers is governed by three-dimensional growth. As the growth proceeded, both the surface morphology and crystallinity recover. The typical FWHM value of(0 0 0 2) omega-rocking curve is 0.46 degrees. The epitaxy relationship is as follows: ZnO(0 0 0 1)parallel to CaF2(1 1 1), and [2 (1) over bar (1) over bar 0]ZnO parallel to[(1) over bar 1 0]CaF2. The e-beam pre-exposure time is optimized by evaluating ZnO overlayers in terms of crystal quality and surface morphology. The optimized e-beam pre-exposure time is determined to be 100 s at an emission current of 20 mu A for a substrate temperature of 600 degrees C. (C) 1999 Elsevier Science B.V. All rights reserved.