  Heterostructures of wurtzite based devices have attracted great research
interests since the tremendous success of GaN in light emitting diodes (LED)
industry. Among the possible heterostructure material candidates, high quality
GaN thin films on inexpensive and lattice matched ZnO substrate are both
commercially and technologically desirable. However, the energy of ZnO polar
surfaces is much lower than that of GaN polar surfaces. Therefore, the
intrinsic wetting condition forbids such heterostructures. As a result, poor
crystal quality and 3D growth mode were obtained. To dramatically change the
growth mode of the heterostructure, we propose to use hydrogen as a surfactant,
confirmed by our first principles calculations. Stable H involved surface
configurations and interfaces are investigated, with the help of newly
developed algorithms. By applying the experimental Gibbs free energy of H$_2$,
we also predict the temperature and chemical potential of H, which is critical
in experimental realizations of our strategy. This novel approach will for the
first time make the growth of high quality GaN thin films on ZnO substrates
possible. We believe that our new strategy may reduce the manufactory cost and
improve the crystal quality and the efficiency of GaN based devices.
