AlGaN-based deep ultraviolet (DUV) multiple-quantum-wells (MQWs) incorporating strain-modulated nanostructures are proposed, demonstrating enhanced degree of polarization (DOP) and improved light extraction efficiency (LEE). The influence of Al composition and bi-axial strains on the optical behaviors of the DUV-MQWs were carefully examined. Compared with planar DUV-MQWs, strain-modulated nanostructure patterned MQWs show three times higher photoluminescence and increased DOP from −0.43 to −0.16. Moreover, nanostructure patterned DUV-MQWs under compressive strains further illustrate higher DOP and LEE values than those under tensile strains due to more efficient diffraction of the guided modes of the transverse electric (TE) polarized light. Our work demonstrates, for the first time, that a combination of compressive in-plane strain and surface nanostructure show unambiguous advantages in facilitating TE mode emission, thus have great promises in the design and optimization of highly efficient polarized DUV optoelectronic devices.

This paper reports investigation on a polarity control scheme of GaN thin films and realization of Schottky barrier diode (SBD) fabricated on a lateral-polarity-structure ('PS) GaN without intentionally doping. Specifically, Ga-polar and N-polar GaN were grown simultaneously side by side on sapphire substrate with patterned AlN buffer. Due to the surface energy difference between two polarities, N-polar regions are n-type conductive with rough surface morphology, while Ga-polar regions are semiinsulating with atomic flat surface morphology. Annealing conditions of both ohmic contact and Schottky contact were investigated. Current-voltage (I-V) characteristic revealed that the SBD fabricated on 'PS GaN has higher forward current, barrier height closer to 0.7 eV, and ideality factor closer to unity compared to SBD fabricated on conventional undoped GaN. The specific on-state resistance (RON) for the SBD based on 'PS GaN is 77 mQ · cm ² lower than the SBD fabricated on conventional GaN. With oxide passivation on SBD surface, forward current exceeds 0.2 A at 10 V, while reverse current is less than 10 ^-5 A at -10 V, respectively. The utilization of 'PS in SBD demonstrates a promising approach for the development of lateral n ⁺ /n ^- SBD with a simple fabrication scheme.

The optical properties of hexagonal GaN microdisk arrays grown on sapphire substrates by selective area growth (SAG) technique were investigated both experimentally and theoretically. Whispering-gallery-mode (WGM) lasing is observed from various directions of the GaN pyramids collected at room temperature, with the dominant lasing mode being Transverse-Electric (TE) polarized. A relaxation of compressive strain in the lateral overgrown region of the GaN microdisk is illustrated by photoluminescence (PL) mapping and Raman spectroscopy. A strong correlation between the crystalline quality and lasing behavior of the GaN microdisks was also demonstrated.