p-type semiconducting MnTe polymorphs: case examples of p-n junction and pFET

Transition metal chalcogenides (TMCs) offer structural diversity and tunable electronic properties, making them attractive for functional semiconductor applications. However, many TMCs exhibit intrinsic n-type or ambipolar conduction, and exploring p-type chalcogenides remains a key challenge. In particular, manganese telluride (MnTe) distinguishes itself by maintaining a p-type behavior across multiple polymorphs. In this study, we demonstrated that MnTe thin films exhibit p-type conduction in both the metastable β-phase (hexagonal wurtzite-type structure) and stable α-phase (hexagonal nickeline-type structure, NiAs-type). Optical spectroscopy revealed band gaps of ≈ 2.35 eV for β-MnTe and ≈ 1.35 eV for α-MnTe. Conversely, hard X-ray photoelectron spectroscopy of the valence band confirmed a Fermi-level alignment consistent with p-type behavior. Moreover, electrical measurements of the MnTe/Al-doped ZnO (n-type) heterojunctions revealed rectifying behavior, confirming the formation of a p-n junction. Furthermore, β-MnTe (metastable phase at room temperature) was successfully employed as a channel material in p-type field-effect transistors, marking the first demonstration of transistor functionality in this polymorph. These results establish MnTe as a rare example of a polymorphic chalcogenide that consistently exhibits p-type conduction and highlight the unique suitability of β-MnTe for transistor applications.