Activating the κ-Ga2O3 surface for epitaxy growth and dopant incorporation using low chemical-hardness metal overlayers

Abstract

Controlling the conductivity of epitaxial κ-Ga2O3 films has been a challenge for its practical applications. Additional indium (In) supply during growth of Ga2O3 can effectively activate donor dopants such as Si and Sn. However, the mechanism behind the activation as well as the In-mediated kinetics of the growth process remains unclear. We employ density functional theory (DFT) calculations to study the atomic-scale kinetics process of κ-Ga2O3(001) epitaxy growth using the isoelectronic metals of Al and In as the surfactants. Only In atoms can promote the crystal growth and dopant activation because the In overlayer keeps staying on the surface during atom deposition. We find that the chemical hardness of a surfactant has a substantial impact on the surface electronic structure. The low chemical hardness of In effectively activates the Ga2O3 surface by shifting up the occupied states and contributing to the hybridization with O near the Fermi level. On the contrary, the high chemical hardness of Al imposes negligible impacts on the occupied electronic states, which leads to strong binding of Al atoms onto the host surface. In atoms play a critical role of electron donor in promoting Ga reduction, which decreases the barrier of substituting a surface Ga atom by a Si or Sn atom. We suggest that only the surfactants chemically softer than the host metal element can enable the substitution and activation of the dopants.