GaN/Al0.5Ga0.5N (11-22) semipolar nanostructures: A way to get high luminescence efficiency in the near ultraviolet range

Abstract

The epitaxial growth of GaN/Al0.5Ga0.5N (11-22) semipolar nanostructures and their structural and optical properties are reported. The nanostructure formation results from a strain induced growth process (Stransky-Krastanov-like growth mode). Atomic force microscopy measurements show that depending on the amount of deposited GaN, the nanostructure shape evolves from an island shape to a string shape aligned along the [1-100] direction. Transmission electron microscopy experiments reveal that (11-20) and (11-23) lateral facets are formed, making with the (11-22) growth plane an angle of 32° and 12°, respectively, and giving a very asymmetric nanostructure shape. Photoluminescence (PL) experiments as a function of the excitation power and temperature show that the internal electric field is very low compared to the case of GaN/Al0.5Ga0.5N (0001) polar quantum dots (QDs). As a consequence, the PL emission is strongly shifted towards the UV range compared to polar QDs and the full width at half maximum of the PL peak is drastically reduced. Furthermore, a room temperature PL nanostructure emission 300 times more intense than that of the semi-polar GaN template is obtained despite a large density of defects in the surrounding matrix, as expected for efficient carrier localization inside the nanostructures. © 2011 American Institute of Physics.