Substrate effects on the heteroepitaxial growth of ZnO thin films by pulsed laser deposition

摘要

Heteroepitaxial ZnO thin films were grown by pulsed laser deposition (PLD) technique on various substrates such as GaN buffered C-plane Al2O3, C-plane Al2O3, A-plane Al2O3, and R-plane Al2O3. Films were formed with a laser fluence of 1.5 J/cm2 at 600 oC in an O2 ambient pressure of 0.5 mTorr. Crystallinity, morphology, and crystallographic orientation relationship of ZnO thin films were investigated by X-ray diffraction and transmission electron microscopy (TEM). X-ray diffraction results showed that ZnO films were grown with (0002) out-of plane orientation on all substrates except on the R-plane Al2O3 substrate where (11-20) oriented domains were dominant. Cross-sectional TEM results showed that all ZnO/substrate systems have sharp interfaces on an atomic level without any indication of interfacial layer. It was observed that ZnO films on GaN, C-Al2O3, and R-Al2O3 substrates have epitaxial orientation relationships of (0001)[2-1-10]ZnO//(0001)[2-1-10]GaN, (0001)[2-1-10]ZnO//(0001)[10-10]C-Al2O3, and (11-20)[0001]ZnO//(10-12)[-1011]R-Al2O3, respectively.