Revealing Self-Driven Broadband Photodetection Using Heterojunction of Bi2Se3 and Low-Temperature Laser Molecular Beam Epitaxy Grown GaN on SrTiO3 (100) Substrate

Optoelectronic properties of GaN are underexplored on good lattice matching SrTiO₃ (STO) due to STO's instability at the high GaN growth temperatures (800–1100 °C) required by traditional techniques. Here, GaN is grown on STO (100) at lower temperatures (500, 600, and 700 °C) using the laser-assisted molecular beam epitaxy (LMBE) technique, and their morphological, crystalline, optical, and photodetection properties are analyzed. Further, heterojunction of Bi₂Se₃ thin film (bandgap of 0.3 eV) is formed on the highest photo-responsive LMBE-GaN/STO to fabricate a self-powered broadband photodetector. The fabricated self-powered heterojunction photodetectors device exhibits a high responsivity of 2.93 × 10² mAW⁻¹ in ultraviolet region and a notable responsivity of 2.3 and 12 mAW⁻¹ in visible and near-infrared spectral regions, respectively. In addition, photoresponse properties of fabricated devices on bare LMBE-GaN and its heterojunction are compared under UV light illumination. The photoresponsivity of heterojunction in UV region is estimated to be 3.05 × 10⁴ mAW⁻¹, which is enhanced by 100% compared to bare LMBE-GaN. Combining the unique optoelectronic properties of GaN and rigidity of STO, epitaxy of GaN on STO enables construction of robust photodetector devices. Further, Bi₂Se₃-functionalized GaN can provide self-sufficient and high-quality futuristic optoelectronics devices.