Homoepitaxial growth of dense ZnO(0001) and ZnO (1120) films via MOVPE on selected ZnO substrates

Deposition via metalorganic vapor phase epitaxy of a low-temperature (480 degrees C) layer followed by a high-temperature (800 degrees C) densification step was employed for the growth of each similar to 200 nm thick, contiguous ZnO(0 0 0 1) layer on a ZnO(0 0 0 1)-oriented substrate. Multiple iterations of this process resulted in films as thick as 2 mu m. Ultra-high-purity (UHP) O-2 served as the principal source of atomic oxygen; however, nitrous oxide (N2O) and nitrogen dioxide (NO2) were also investigated as potential oxygen sources in the pure state as well as in mixtures with oxygen produced in the chamber and for nitrogen doping of the growing (0 0 0 1) films. Carbon and hydrogen, derived from the decomposition of the diethylzinc precursor, and N were incorporated into the films primarily during the low-temperature step. Films grown using N2O + O-2 contained an average of 5 x 10(17) cm(-3) atomic nitrogen; films using NO2 + O-2 had an average nitrogen concentration of 9 x 10(19) cm(-3). The low-temperature growths on ZnO(0 0 0 1) using O-2 and NO2 + O-2 resulted in the formation of a needle microstructure; a spaghetti-like network microstructure formed when using N02 + 02 at the same temperature. Lateral growth at 800 degrees C from sites within the needle and network microstructures resulted in dense films containing shallow hexagonal pits that increased in number and depth with an increase in film thickness. Triple-axis XRD measurements indicated that the crystal structure of the films mimic the underlying substrates. Growth on [1 12 0]oriented ZnO substrates at the single temperature of 600 degrees C resulted in a dense film composed of needles oriented inplane along [0 0 0 1]. Atomic force microscopy and secondary ion mass spectroscopy revealed an rms value of 5.4 nm and hydrogen of concentration of 6.5 x 10(18) with the carbon concentration below the detection limit of 1.3 x 10(19) atoms/cm(3). (c) 2005 Elsevier B.V. All rights reserved.