High‐Performance Photodetector Based on Bi₂Se₃/GeSe Heterojunction with Band Alignment Evolution

Abstract Band alignment engineering in 2D van der Waals heterostructures is a promising method for manufacturing high‐speed, high‐responsivity, and high‐gain photodetectors. Here, a heterojunction photodetector with the band alignment transition from type I to type II under the bias voltage using narrow bandgap material n‐Bi₂Se₃ and polarization‐sensitive material p‐GeSe is designed and prepared. This photodetector possesses excellent performance of broadband detection (532‐1550 nm), high responsivity (5.86 × 10³ A W⁻¹), high detectivity (1.50 × 10¹³ Jones), significant external quantum efficiency (1.15 × 10⁶%) and fast response time (97 µs). Compared with the conventional type II band alignment, an additional triangular potential barrier is generated in this type II band alignment evolved from type I. Notably, this triangular barrier will block photogenerated carriers in Bi₂Se₃, which leads to high external quantum efficiency; Furthermore, photogenerated holes can tunnel through this barrier, effectively shortening the response time. Meanwhile, the device can achieve polarization detection (anisotropic ratio = 1.74 at 808 nm) and polarization imaging, which is of great significance for reducing the bit error rate in complex environments.