Low temperature epitaxial growth of ZnO layer by plasma-assisted epitaxy

Plasma-assisted epitaxial growth of ZnO layers were achieved on C- and R-pl ane sapphire substrates in oxygen plasma excited by radio frequency power a t 13.56 MHz with evaporation of pure elemental Zn, The ZnO layers were grow n at 300-100 degrees C with high growth rate around 1.7 mu m/h. Surface cle aning of sapphire substrates using Ar-plasma was crucial for good quality Z nO growth. Photoluminescence spectra at 10 Ii were dominated by band-edge e mission due to bound excitons without deep level emission in green-light re gion. The intensity of band-edge emission was strongly dependent on applied radio frequency power to excite Ar- and O-2-plasma for sapphire surface cl eaning and ZnO growth, respectively, and was about 50 times larger on the l ayer grown in oxygen plasma than that grown in non-excited oxygen gas. The ZnO layer grown on R-plane sapphire was epitaxially grown above 300 degrees C in oxygen plasma, however, on C-plane sapphire the ZnO layer was easily polycrystallized for thick films even at 400 degrees C. Growth mode and sur face morphology of ZnO layers were drastically changed with the substrate o rientation. (C) 1999 Elsevier Science S.A. All rights reserved.