Abstract
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.
Highlights
III-nitride semiconductors grown along nonpolar orientations have attracted extensive interest in recent years, due to a few unique properties in comparison with their c-plane polar counterparts, especially for InGaN-based emitters
We demonstrate nonpolar InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) grown on such high quality nonpolar GaN templates
Standard photoluminescence (PL) measurement is performed at room temperature using a 375 nm diode laser to excite the nonpolar LED sample, with the luminescence dispersed by a 0.55 m monochromator and detected by a charge-coupled device (CCD)
Summary
III-nitride semiconductors grown along nonpolar orientations have attracted extensive interest in recent years, due to a few unique properties in comparison with their c-plane polar counterparts, especially for InGaN-based emitters. Nonpolar InGaN emitters exhibit another major advantage which current c-plane ones lack, their polarized light source, which results from the valence band splitting generated by anisotropic biaxial stress[7,8]. This will play an important role in manufacturing backlighting in terms of improving power consumption and compactness[9], as current approach is to insert a polarizer and up to 30% optical power is wasted. Our group has achieved high quality nonpolar (11–20) GaN films by using an overgrowth approach on regularly arrayed (11–20) GaN micro-rods on r-plane sapphire[19]. Optical and polarization properties are investigated by photoluminescence (PL), Confocal PL, and polarized electroluminescence (EL) measurements
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