The effect of different oriented sapphire substrates on the growth of polar and non-polar ZnMgO by MOCVD

Polar and non-polar ZnMgO were synthesized on different crystallographic planes (C-, R- and M-planes) of sapphire (Al2O3) substrates by metal organic chemical vapor deposition, respectively. Under the same experimental condition, polar ZnMgO nanorods were obtained on C-Al2O3 substrate whereas non-polar ZnMgO thin films were obtained on R- and M-Al2O3 substrates. The surface morphology was significantly influenced by the competition of the preferable growth directions on different sapphire substrates. On C-Al2O3 substrate, ZnMgO nanorods were vertically well-aligned with typical lengths in the range 330-360 nm. On R- and M-Al2O3 substrates, however, ZnMgO thin films with flat surfaces were obtained, whose thickness were 150 and 20 nm, respectively. Under the same condition, the C-ZnMgO deposited on C-Al2O3 substrate has the maximum growth velocity (11 nm/nim), followed by A-ZnMgO deposited on R-Al2O3 substrate (5 nm/min), and the M-ZnMgO deposited on M-Al2O3 substrate has the minimum one (0.67 nm/min). The Near-Band-Edge (NBE) emission in Photoluminescence (PL) spectra shows a clear blueshift and a slight broadening compared with that of pure ZnO samples, which suggest that the Mg content has successfully incorporated into ZnO. The different energy blueshifts (67 meV and 98 meV) of the NBE emission demonstrate that A-ZnMgO deposited on R-Al2O3 substrate has higher Mg incorporation efficiency than C-ZnMgO on C-Al2O3 substrate.