Plasma-assisted molecular beam epitaxy of SnO(001) films: Metastability, hole transport properties, Seebeck coefficient, and effective hole mass

Among semiconducting materials transparent semiconducting oxides have gained increasing attention within the last decade. While most of these oxides can be only doped n-type with room-temperature electron mobilities on the order of 100cm2V−1s−1, p-type oxides are needed for the realization of pn-junction devices but typically suffer from excessively low (≪1 cm2V−1s−1) hole mobilities. Tin monoxide (SnO) is one of the few p-type oxides with higher hole mobility, yet is currently lacking a well-established understanding of its hole transport properties. Moreover, growth of SnO is complicated by its metastability with respect to SnO2 and Sn, requiring epitaxy for the realization of single crystalline material typically required for high-end applications. Here, we give a comprehensive account on the epitaxial growth of SnO, its (meta)stability, and its thermoelectric transport properties in the context of the present literature. Textured and single-crystalline, unintentionally doped p-type SnO(001) films are grown on Al2O3(00.1) and Y2O3-stabilized ZrO2(001), respectively, by plasma-assisted molecular beam epitaxy, and the epitaxial relations are determined. The metastability of this semiconducting oxide is addressed theoretically through an equilibrium phase diagram. Experimentally, the related SnO growth window is rapidly determined by an in situ growth kinetics study as a function of Sn-to-O-plasma flux ratio and growth temperature. The presence of secondary Sn and SnOx(1