Tuning the electrical properties of unintentionally doped epitaxial p -type α-SnO thin films while maintaining a shallow hole ionization energy

We demonstrate the growth of unintentionally doped p-type α-SnO (001) thin films by suboxide molecular-beam epitaxy at low growth temperatures of 330–360 °C without additional oxygen supply. By increasing the SnO flux, the hole concentration increases from 0.2 × 1018 to 1.3 × 1018 cm−3, while the hole mobility decreases from 8.5 to 3.9 cm2 V−1 s−1. The dependence of electrical properties on SnO flux is attributed to the associated changes in the chemical potential of SnO during growth, which likely influences the formation of tin vacancies and, therefore, the hole concentration. Similar trends were also observed under an added oxygen background pressure, although the effects were less pronounced. At a fixed SnO flux, the hole mobility increases with increasing growth temperature; however, higher deposition temperature inevitably leads to increased surface roughness. Temperature-dependent Hall measurements reveal a shallow apparent activation energy of 15.2–22.7 meV across the (0.1–8) × 1013 molecules cm−2 s−1 range of SnO fluxes investigated.