Simple processing of ZnO from solution: Homoepitaxial film and bulk single crystal

The system LiCl-ZnCl₂-K₂CO₃ is employed to fabricate homoepitaxial (0001) ZnO films by liquid phase epitaxy (LPE). The effect of ZnO concentration in the solution on the microstructure of the film is analyzed. Transition of growth modes was observed, evolving from island growth at <2 mmol of ZnO per 1 mol of LiCl over columnar growth (free-standing columns at 2.5 ± 0.5 mmol, porous film at 3.5 ± 0.5 mmol, and fully coalesced film at 5 mmol of ZnO) to step-flow growth at 12 ± 0.5 mmol of ZnO. Single-crystalline films, X-ray full-width half-maximum (FWHM) of 25 arcsec for (0002) reflection, with steps propagating over macroscopic dimensions were fabricated in the concentration range 12.5-14 mmol of ZnO. A structural quality factor (SQF) was introduced for joint description of both surface roughness and X-ray crystallinity. SQF is highest for films grown at 13 mmol of ZnO. Doping with bi-, tri- and tetravalent cationic additives yields ZnO films, the luminescent characteristics of which are investigated in comparison to low-alkaline hydrothermal ZnO. Hydrothermal synthesis under subcritical conditions at < 150 °C has been investigated as a fast tool for doping of thermodynamically stable ZnO. Low-temperature luminescence is compared to hydrothermal bulk ZnO crystal grown under supercritical conditions.