Controlling the p-type conductivity of α-SnO thin films by potassium doping

Development of a high-performance, p-type oxide channel is crucial to realize all-oxide complementary metal–oxide semiconductor technology that is amenable to 3D integration. Among p-type oxides, α-SnO is one of the most promising due to its relatively high hole mobility (as high as 21 cm²/Vs has been reported), back-end-of-line compatible processing temperature (≤400 °C), and good optical transparency for visible light. Unfortunately, doping control has been demonstrated over a limited range of hole concentrations in α-SnO films. First-principles calculations identify potassium substitution on the tin site (K_Sn) of α-SnO to be a promising acceptor that is not (self)-compensated by native vacancies or potassium interstitials (K_i). Here, we synthesize epitaxial K-doped α-SnO thin films with controlled doping concentrations using suboxide molecular-beam epitaxy. Potassium doping provides systematic control of hole doping in α-SnO thin films over the range of 4.8 × 10¹⁷ to 1.5 × 10¹⁹ cm⁻³ without significant degradation of hole mobility or the introduction of states that absorb visible light. Temperature-dependent Hall measurements reveal that the potassium is a shallow acceptor in α-SnO with an ionization energy in the 10–20 meV range.