Temperature dependence of Zn1−xMgxO films grown on c-plane sapphire by metal organic vapor phase epitaxy

Metal organic vapor phase epitaxy (MOVPE) has been used to grow ternary Zn1−xMgxO layers on c-plane sapphire substrates. The precursors nitrous oxide, bismethylcyclopentadienyl magnesium, and dimethylzinc-triethylamine were used as the oxygen, magnesium, and zinc sources, respectively. Nitrogen was the carrier gas. The concentration of magnesium in the gas phase was varied, relative to the zinc concentration, by adjusting the partial pressures ratio RII=PMg/(PMg+PZn). Both RII and substrate temperature variations induce a strong dependence of the growth rate, structural and optical qualities, and magnesium content in the grown layer. When the RII ratio is increased from 0 to 0.8 at different substrate temperatures, the following are clearly observed: (i) a decrease of the growth rate, (ii) a shift of the Zn1−xMgxO (0 0 2) X-ray diffraction peak to higher diffraction angles from 34.44° (wurtzite ZnO) up to 34.63°, and (iii) a shift of the PL-near band edge emission from 3.36 eV (ZnO bandgap) up to 3.75 eV. This latter value corresponds to a magnesium concentration in the Zn1−xMgxO solid solution of approximately 20%.