Defect effect on the performance of nonpolar GaN-based ultraviolet photodetectors

Abstract

The anisotropy of GaN(11-20) makes it possible to fabricate polarized ultraviolet (UV) photodetectors (PDs) for applications in fields such as remote sensing and airborne astronomical navigation. The defect density has a significant effect on the performance of GaN(11-20)-based UV PDs. However, the mechanism through which different defects and their densities affect the performance of these devices is unclear. Therefore, in this work, we investigated the mechanisms of the screw or mixed dislocation, edge dislocation, and basal stacking fault (BSF) densities affecting the dark current, responsivity, and response time of GaN (11-20)-based PDs, respectively. We observed that the screw or mixed dislocation increased the dark current mainly through reducing the Schottky barrier height and forming leakage current, whereas the edge dislocation and BSF decreased the responsivity by reducing the electron mobility. Furthermore, all the three types of defects increased the response time through forming traps to recombine the holes with electrons and thus delaying the escape of carriers. These results are highly significant for developing nonpolar GaN-based UV PDs.

Non-Polar Gallium Nitride for Photodetection Applications: A Systematic Review

“…They reported the preparation of patterned Si substrate by PECVD, followed by the epitaxial growth of GaN microwires with the use of an Aixtron 3 × 2" showerhead MOCVD reactor (Thomas Swan Scientific Equipment Ltd.). Apart from that, the effect of the dislocations and BSFs of the epitaxial layer grown by MOCVD towards the performance of a-plane GaN-based photodetectors in terms of electrical properties was reported [31]. Another significant finding of catalyst-free n-doped GaN NWs grown by MOCVD was reported by Zhang et al [55].…”

“…The adaptation of an r-plane sapphire substrate for a-plane GaN growth uncovered new studies and techniques. More interestingly, the behavior of the a-plane GaN epitaxial layer towards the extended defects was investigated [31]. In particular, the dislocation densities and basal stacking faults (BSFs) that hindered the electrical performance of the a-plane GaN-based photodetector were greatly reduced.…”

“…In addition, the electrical performance of a fabricated MSM a-plane GaN photodetector with Au/Ni as the metal contact was studied [31,32]. The mechanisms of the screw or mixed dislocation, edge dislocation, and BSF densities that affected the dark current, responsivity, and response time of GaN (112 0)-based photodetectors were discussed.…”

“…Therefore, a non-polar GaN-based photodetector would exhibit a faster response with higher efficiency. Several groups have reported the use of the non-polar growth direction to produce GaN-based photodetectors along the non-polar direction as an alternative for c-orientated photodetectors [19,23,[30][31][32]. However, it is noteworthy that non-polar GaN grown on sapphire or silicon (Si) substrates portrayed low crystal quality (far from device requirement) with a broad full width at half maximum (FWHM) of ∼0.5-0.6 • as compared to the c-orientated GaN growth (less than 0.1 • ) [2,7,19,23,30,[33][34][35].…”

“…However, it is noteworthy that non-polar GaN grown on sapphire or silicon (Si) substrates portrayed low crystal quality (far from device requirement) with a broad full width at half maximum (FWHM) of ∼0.5-0.6 • as compared to the c-orientated GaN growth (less than 0.1 • ) [2,7,19,23,30,[33][34][35]. This is mainly attributed to the anisotropic crystallographic mismatch owing to dissimilar lattice structures and mismatches in the coefficients of thermal expansion between non-polar GaN epitaxial layers and the substrates [19,23,31,36,37]. Consequently, high generated densities of defects and dislocations in the non-polar GaN epitaxial layer could impair the devices' efficiency, such as response of rise and fall time, compared to c-plane photodetectors [38][39][40][41].…”