Dual-band persistent photoconductive effect of GaN-based van der Waals heterojunctions

GaN-based hybrid-dimensional heterojunctions play a critical role in optoelectronics; however, their persistent photoconductivity (PPC)—essential for synaptic devices—has been limited to the UV regime by the wide bandgap of GaN. We report the photoconductive properties of dual-channel heterojunction devices composed of MoS2 and WSe2 integrated with GaN. Specifically, the GaN/WSe2 heterojunction did not exhibit a PPC effect under 633 nm light, while the GaN/MoS2 heterojunction displayed a pronounced PPC effect. Notably, the introduction of h-BN intercalation resulted in the GaN/h-BN/MoS2 heterojunction lacking the PPC effect. This paper analyzes the capture and excitation of carriers by CN defect states in GaN and demonstrates that the built-in electric field of the heterojunction influences the separation of photo-generated carriers, resulting in distinct PPC behaviors among various devices. Through h-BN intercalation, the pivotal role of interlayer interaction in extending the response wavelength of GaN-based optoelectronic synapses has been unambiguously identified. This work establishes a mechanistic foundation and design principle for GaN-based hybrid-dimensional optoelectronic synapses, extending their operating wavelength and enabling multi-band neuromorphic computing.