High responsivity and low dark current nonpolar GaN-based ultraviolet photo-detectors†
The nonpolar a-plane and m-plane of GaN are anisotropic due to the fact that in-plane stresses of nonpolar GaN along different directions are varied, which is considered to be the reason why they are chosen for the preparation of polarization-sensitive ultraviolet (UV) photo-detectors (PDs), etc., when compared to polar c-plane GaN-based UV PDs. However, the nonpolar GaN-based UV PDs suffer from poor-quality GaN epitaxial films, which limit their performance enhancement. Herein, we report the fabrication of high responsivity and low dark current nonpolar a-plane GaN-based metal-semiconductor–metal (MSM) UV PDs, by using high-quality a-plane GaN epitaxial films grown on r-plane sapphire substrates through control of the dislocation density. The ∼2.5 μm-thick GaN epitaxial films were grown by the combination of low-temperature pulsed laser deposition and high-temperature metal–organic chemical deposition technologies and were then fabricated into MSM UV PDs. The MSM UV PDs were revealed to have a high responsivity of 0.74 A W−1 and a low dark current of 1.3 nA at an applied bias of 2 V, as well as a very small full-width at half-maximum for GaN(11-20) of 360 arcsec. The performance is better than the results for all of the nonpolar GaN-based MSM UV PDs ever reported. These UV PDs shed light on the potential for wide applications.