Type-II band alignment and enhanced optical properties in InP/Bi ₂ Se ₃ van der Waals heterojunctions: a first-principles and FDTD study

In this paper, a novel InP/Bi₂Se₃ van der Waals heterojunction (vdWH) was constructed, and its geometric, electrical, interface, and optical properties were precisely calculated using first-principles calculations and finite-difference time-domain (FDTD). These results showed that this vdWH has excellent light absorption in the infrared range. The stability of the InP/Bi₂Se₃ vdWH was verified via binding energy calculations, elastic constant determination, phonon spectrum analysis, and ab initio molecular dynamics simulations (AIMD). The results demonstrated that the InP/Bi₂Se₃ vdWH has a type-II staggered band alignment with an indirect bandgap of 0.745 eV, and the bandgap can be tuned under the regulation of external strain and electric field. Moreover, the InP/Bi₂Se₃ vdWH possessed excellent carrier mobility, with electron mobilities of up to 4256.55 cm² V⁻¹ s⁻¹ and 4194.46 cm² V⁻¹ s⁻¹ in the x and y directions and hole mobilities of 2130.09 cm² V⁻¹ s⁻¹ and 2258.32 cm² V⁻¹ s⁻¹, and the absorption was also significantly enhanced, reaching 6.767 × 10⁴ cm⁻¹ under the irradiation of an incident light wave of 1.5 eV. Furthermore, the InP/Bi₂Se₃ vdWH photodetector was designed and modeled by FDTD. In addition, the calculation results indicated that the infrared light absorption of this vdWH-based photodetector reaches up to 60%, and the position of the maximum absorption peak is adjustable. The photocurrent density of this device in the near-infrared region was calculated to be 14.7 mA cm⁻². In conclusion, this study confirmed that the InP/Bi₂Se₃ vdWH possesses remarkable competitiveness in the field of next-generation infrared detection.