Fabrication of homoepitaxial ZnO films by low-temperature liquid-phase epitaxy

Highly crystalline undoped ZnO films were grown by liquid-phase epitaxy on (0 0 0 1) ZnO substrates with a misorientation of 0.5° toward 〈101¯0〉. ZnO was continuously formed by the chemical reaction of ZnCl2 and K2CO3. Films of thickness ⩽4 μm were grown in the temperature range 630–640 °C, resulting in step-flow growth as observed by differential interference microscopy and scanning electron microscopy. An interstep distance of 2±0.5 μm and step height 0.5 nm corresponding to one monolayer was observed by atomic force microscopy. Measurement of the (0 0 0 2) reflection of the X-ray rocking curve revealed the high quality of the ZnO films with a full-width half-maximum of 31 arcsec. The photoluminescence spectrum obtained at 4 K is dominated by emission from the band edge at 3.36 eV with a sharp splitting of the free exciton emission. A damaged surface layer in the ZnO substrate due to machining was revealed by radioluminescence at 80 K.