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.

Nonpolar n-ZnO/p-GaN heterojunction light emitting diode has been demonstrated with a-plane (112¯0) ZnO active layer grown by a facile low-cost solution growth method at low temperature of 90 °C. High quality nonpolar ZnO planar film without seed layer was directly formed on a-plane GaN template due to the anisotropic growth rates along the specific crystallographic directions. The turn on voltage of the device was as low as 3 V, and narrow stable UV-blue electroluminescence emissions with peak wavelength of 392 to 420 nm under various forward bias conditions at room temperature were observed.

To investigate the effects of their surface recovery and optical properties, extremely small sized (12 µm × 12 µm mesa area) red AlGaInP micro light emitting diodes ($$\upmu$$ μ LED) were fabricated using a diluted hydrofluoric acid (HF) surface etch treatment. After the chemical treatment, the external quantum efficiencies (EQEs) of $$\upmu$$ μ -LED at low and high injection current regions have been improved by 35.48% and 12.86%, respectively. The different phenomena of EQEs have a complex relationship between the suppression of non-radiative recombination originating from the etching damage of the surface and the improvement of light extraction of the sidewalls. The constant enhancement of EQE at a high injection current it is attributed to the expansion of the active region’s sidewall surface area by the selective etching of AlInP layers. The improved EQE at a low injection current is related to the minimization of the surface recombination caused by plasma damage from the surface. High-resolution transmission electron microscopy (HR-TEM) revealed physical defects on the sidewall surface, such as plasma-induced lattice disorder and impurity contamination damage, were eliminated using chemical treatment. This study suggests that chemical surface treatment using diluted HF acid can be an effective method for enhancing the $$\upmu$$ μ -LED performance.

Abstract:We report on the observation of carrier-diffusion-induced defect emission at high excitation density in a-plane InGaN single quantum wells. When increasing excitation density in a relatively high regime, we observed the emergence of defect-related emission together with a significant reduction in bandedge emission efficiency. The experimental results can be well explained with the density-activated carrier diffusion from localized states to defect states. Such a scenario of density-activated defect recombination, as confirmed by the dependences of photoluminescence on the excitation photon energy and temperature, is a plausible origin of efficiency droop in a-plane InGaN quantum-well light-emitting diodes. a cfzhang@nju.edu.cn b jskwak@sunchon.ac.kr c mxiao@uark.edu

Efficiency droop is a major obstacle facing high-power application of InGaN/GaN quantum-well (QW) light-emitting diodes (LEDs). In this paper, we report the suppression of efficiency droop induced by the process of density-activated defect recombination in nanorod structures of a-plane InGaN/GaN QWs. In the high carrier density regime, the retained emission efficiency in a dry-etched nanorod sample is observed to be over two times higher than that in its parent QW sample. We further argue that such improvement is a net effect that the lateral carrier confinement overcomes the increased surface trapping introduced during fabrication.