Material Design of Green-Light-Emitting Semiconductors: Perovskite-Type Sulfide SrHfS3

A current issue facing light-emitting devices is a missing suitable material for green emission. To overcome this, we explore semiconductors possessing (i) a deep conduction band minimum (CBM) and a shallow valence band maximum (VBM), (ii) good controllability of electronic conductivity and carrier polarity, and (iii) a directly allowed band gap corresponding to green emission. We focus on early transition metal (eTM)-based perovskites. The eTM cation’s high and stable valence state makes its carrier controllability easy, and the eTM’s nonbonding d orbital and the anion’s p orbital, which constitute the deep CBM and shallow VBM, are favorable to n- and p-type doping, respectively. To obtain a direct band gap, we applied a scheme that folds the bands constituting the VBM at the zone boundary to the zone center where the CBM appears. Orthorhombic SrHfS3 was chosen as the candidate. The electrical conductivity was tuned from 6 × 10–7 to 7 × 10–1 S·cm–1 with lanthanum (La) doping and to 2 × 10–4 S·cm–1 with phosphorus (P) doping. Simultaneously, the major carrier polarity was controlled to n type by La doping and to p type by P doping. Both the undoped and doped SrHfS3 exhibited intense green photoluminescence (PL) at 2.37 eV. From the PL blue shift and short lifetime, we attributed the emission to a band-to-band transition and/or exciton. These results demonstrate that SrHfS3 is a promising green-light-emitting semiconductor.