Optical and polarization properties of nonpolar InGaN-based light-emitting diodes grown on micro-rod templates

We have demonstrated non-polar a-plane InGaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) on sapphire, achieved by overgrowing on a micro-rod template with substantially improved crystal quality. Photoluminescence measurements show one main emission peak at 418 nm along with another weak peak at 448 nm. Wavelength mapping measurements carried out by using a high spatial-resolution confocal PL system indicate that the two emissions origin from different areas associated with the underlying micro-rod patterns. Electroluminescence measurements exhibit a negligible blue-shift of 1.6 nm in the peak wavelength of the main emission when the driving current increases from 10 to 100 mA, indicating that the quantum confined Stark effect is effectively suppressed in in the nonpolar LED. A polarization ratio of 0.49 is obtained for the low-energy emission (~448 nm), while the main emission (~418 nm) shows a polarization ratio of 0.34. Furthermore, the polarization ratios are independent of injection current, while the energy separation between m-polarized and c-polarized lights increases with the injection current for both emissions.