High crystalline a-plane (112¯0) GaN epitaxial layers with smooth surface morphology were grown on r-plane (11¯02) sapphire substrate by metalorganic chemical vapor deposition. The full width at half maximum of x-ray rocking curve was measured as 407 arc sec along c-axis direction, and the root mean square roughness was 1.23 nm. Nonpolar a-plane InGaN/GaN light emitting diodes were subsequently grown on a-plane GaN template, and the optical output power of 0.72 mW was obtained at drive current of 20 mA (3.36 V) and 2.84 mW at 100 mA (4.62 V) with the peak emission wavelength of 477 nm.

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The properties of Ti/Al/Ni/Au Ohmic contacts on n-type a-plane GaN epitaxial layers directly grown on r-plane sapphire substrates are reported. The minimum specific contact resistance of ∼10−5 Ω cm2 was achieved after annealing at 650–700 °C. Ohmic contact properties were measured using transmission line method patterns oriented in both the m- and c-axis directions of a-plane GaN. The sheet resistance of a-plane GaN along the c-axis was two times higher than that along the m-axis, which shows significant electric anisotropy in the two orientations.

The extraction efficiency of nonpolar a-plane (11-20) GaN LEDs on sapphire substrates has been enhanced by selectively etching the mesa sidewall faces and the n-type GaN surfaces with photoenhanced chemical wet etching. Submicron-sized trigonal prisms having prismatic planes of {1-100} were clearly displayed on the n-type GaN surfaces as well as the sidewall face after 5 min etching at 60 degrees C. The radiation patterns have shown that more light is extracted in all directions and the output powers of surface textured a-plane GaN LEDs have increased by 25% compared with control samples. PEC wet etching produced unique feature of etching morphology on the mesa sidewall faces and the n-type GaN surface.