In-plane anisotropic photoconduction in nonpolar epitaxial a-plane GaN

Nonpolar a-plane GaN epitaxial films were grown on an r-plane sapphire using plasma-assisted molecular beam epitaxy (PAMBE) system, with various nitrogen plasma power conditions. The crystallinity of the films was characterized by high-resolution X-ray diffraction and reciprocal space mapping. Using the X-ray ‘rocking curve - phi scan’, [0002], [1-100] and [1-102] azimuth angles were identified and interdigitated electrodes (IDEs) along these directions were fabricated to evaluate the direction-dependent UV photoresponses. UV responsivity (R) and internal gain (G) were found to be dependent on the azimuth angle and in the order of [0002] > [1-102] > [1-100], which has been attributed to the enhanced crystallinity and lowest defect density along [0002] azimuth. The temporal response was very stable irrespective of growth conditions and azimuth angles. Importantly, response time, responsivity and internal gain were 210 ms, 1.88 AW−1 and 648.9%, respectively even at a bias as low as 1 V. The results were val...