The band-edge excitons observed in few-layer NiPS3
Ching‐Hwa Ho, Tien-Yao Hsu, Luthviyah Choirotul Muhimmah
Abstract
Abstract Band-edge excitons of few-layer nickel phosphorous trisulfide (NiPS 3 ) are characterized via micro-thermal-modulated reflectance (μTR) measurements from 10 to 300 K. Prominent μTR features of the A exciton series and B are simultaneously detected near the band edge of NiPS 3 . The A exciton series contains two sharp A 1 and A 2 levels and one threshold-energy-related transition (direct gap, E ∞ ), which are simultaneously detected at the lower energy side of NiPS 3 . In addition, one broadened B feature is present at the higher energy side of few-layer NiPS 3 . The A series excitons may correlate with majorly d -to- d transition in the Rydberg series with threshold energy of E ∞ ≅ 1.511 eV at 10 K. The binding energy of A 1 is about 36 meV, and the transition energy is A 1 ≅ 1.366 eV at 300 K. The transition energy of B measured by μTR is about 1.894 eV at 10 K. The excitonic series A may directly transit from the top of valence band to the conduction band of NiPS 3 , while the B feature might originate from the spin-split-off valence band to the conduction band edge. The direct optical gap of NiPS 3 is ~1.402 eV at 300 K, which is confirmed by μTR and transmittance experiments.