Role of hydrogen in molecular beam epitaxy of ZnO

The role of hydrogen in the growth and material properties of ZnO films grown at temperature as low as 300 deg. C by plasma-assisted molecular beam epitaxy with and without hydrogen irradiation was investigated. Results showed that during growth, the surface morphology changed from small hemispherical grains (10 nm) to large hexagonal islands (100 nm) by molecular hydrogen irradiation. The observed changes in the surface morphology correlated with the surface migration length of Zn adatoms on the surface with or without H termination. X-ray diffraction and photoluminescence measurements showed that the structural and optical properties of ZnO films were significantly improved by H2 irradiation during growth and that the ZnO films grown here at low temperature (300 deg. C) by H2 irradiation had crystalline quality as high as that of ZnO grown at higher temperature (600 deg. C) without H2 irradiation. Secondary ion mass spectrometry and Hall effect measurements indicated that most of hydrogen incorporated in the ZnO films grown here did not act as shallow donors