Interfacial photoconductivity effect of type-I and type-II Sb2Se3/Si heterojunctions for THz wave modulation

Abstract

An in-depth understanding of the photoconductivity and photocarrier density at the interface is of great significance for improving the performance of optoelectronic devices. However, extraction of the photoconductivity and photocarrier density at the heterojunction interface remains elusive. Herein, we have obtained the photoconductivity and photocarrier density of 173 nm Sb2Se3/Si (type-I heterojunction) and 90 nm Sb2Se3/Si (type-II heterojunction) utilizing terahertz (THz) time-domain spectroscopy (THz-TDS) and a theoretical Drude model. Since type-I heterojunctions accelerate carrier recombination and type-II heterojunctions accelerate carrier separation, the photoconductivity and photocarrier density of the type-II heterojunction (21.8 × 104 S⋅m−1, 1.5 × 1015 cm−3) are higher than those of the type-I heterojunction (11.8 × 104 S⋅m−1, 0.8 × 1015 cm−3). These results demonstrate that a type-II heterojunction is superior to a type-I heterojunction for THz wave modulation. This work highlights THz-TDS as an effective tool for studying photoconductivity and photocarrier density at the heterojunction interface. In turn, the intriguing interfacial photoconductivity effect provides a way to improve the THz wave modulation performance.