Improvement in the crystallinity of ZnO thin films by introduction of a buffer layer (original) (raw)

The influence of pre-deposition of homo-buffer layers on film quality is studied as functions of temperature and duration of pre-deposition, for zinc oxide (ZnO) crystalline films prepared by pulsed laser deposition on sapphire (0 0 0 1) substrates. This preparation technique is necessary to prepare high quality films suitable for the development of ZnO devices. Crystallinity and surface morphology were characterized by X-ray diffraction (XRD), reflection high energy electron diffraction and scanning electron microscopy. The line width of the rocking curve observed for ZnO (0 0 0 2) XRD of ZnO films decreases (to 0.098 from 0.2-0.38) upon introduction of a buffer layer of ZnO itself at a low temperature approximately 500 8C, indicating the formation of high quality films. The surface morphology and flatness were also improved. The film prepared under optimal conditions shows a high optical transmittance of ;90% with a steep falloff at 380 nm and a fairly small carrier concentration (1.8=10 17 cm ). These results imply that the buffer layer relaxes the strain due to lattice mismatch between ZnO and sapphire (by 18%) y3 and improves the film crystallinity. ᮊ