Wide-Gap p-Type Layered Oxychalcogenides AE2CuInO3Ch (AE: Alkaline Earth; Ch: Chalcogen): Unusually Low Residual Carrier Concentration and Green-to-Red Emission

The absence of efficient green–yellow light emission in III-V group semiconductors, (Al,Ga,In)-(N,P,As), is a serious issue of inorganic solid-state light-emitting devices. A series of layered Cu-based oxychalcogenides, LaCuOCh (Ch = chalcogen), is known as wide-gap (E_g = 2.4–3.1 eV) p-type semiconductors exhibiting high optoelectronic performance such as high hole mobilities and excitonic blue emission even at room temperature. However, they cannot reduce the residual carrier concentration similar to many oxide and chalcogenide semiconductors. In this paper, we demonstrate that layered oxychalcogenides, AE₂CuInO₃Ch (AE = Sr and Ba; Ch = S, Se, and Te), exhibit p-type semiconductor properties and green-to-red light emission. The room-temperature electronic conductivity (σ) of Sr₂CuInO₃Ch is significantly suppressed from 1.8 × 10⁰ to 1.9 × 10^–4 S/cm by substituting Ch with Te to Ch with S. Exceptionally, Ba₂CuInO₃S exhibits a highly resistive state with σ = 1.9 × 10^–9 S/cm, originating from an unusually reduced residual hole concentration of ∼10¹³ cm^–3, which is totally different from other Cu-based (oxy)chalcogenide semiconductors including LaCuOCh. First-principles defect calculations reveal that the source of holes is Cu vacancy, while In_Cu antisite and S vacancy work as coexisting donor-type defects and compensate the generated holes, leading to the stable low carrier concentrations. Furthermore, AE₂CuInO₃Ch exhibit green, orange, and red emission owing to their direct-transition-type E_g of 1.2–2.2 eV. Thus, AE₂CuInO₃Ch are new promising candidate semiconductors for a visible light source.