In-Plane Anisotropic Photoconduction in Nonpolar Epitaxial a-Plane GaN.

Area of Science:

• Materials Science
• Semiconductor Physics
• Optoelectronics

Background:

• Nonpolar Gallium Nitride (GaN) films are crucial for optoelectronic devices.
• Understanding crystal orientation's impact on GaN properties is essential for device optimization.

Purpose of the Study:

• To investigate the influence of nitrogen plasma power on nonpolar a-plane GaN film growth.
• To evaluate the direction-dependent ultraviolet (UV) photoresponse of these GaN films.
• To correlate film crystallinity and defect density with photoresponse characteristics.

Main Methods:

• Growth of nonpolar a-plane GaN epitaxial films on r-plane sapphire via plasma-assisted molecular beam epitaxy.
• Crystallinity characterization using high-resolution X-ray diffraction and reciprocal space mapping.
• Fabrication of interdigitated electrodes along specific azimuth angles ([0002], [1-100], [1-102]) for photoresponse measurements.
• Device simulation using Silvaco Atlas to validate experimental findings.

Main Results:

• UV responsivity and internal gain are azimuth-angle dependent, following the order [0002] > [1-102] > [1-100].
• The [0002] azimuth demonstrated enhanced crystallinity and the lowest defect density, correlating with superior photoresponse.
• Stable temporal response was observed across different growth conditions and azimuth angles.
• High performance metrics (210 ms response time, 1.88 A/W responsivity, 648.9% gain) achieved at a low bias of 1 V.

Conclusions:

• The UV photoresponse of nonpolar a-plane GaN films is significantly influenced by crystallographic orientation.
• Optimizing growth conditions to enhance crystallinity along specific azimuths, like [0002], is key for improved device performance.
• Further research into in-plane crystal anisotropy is needed for advanced UV detector applications.