Growth and characterization of a-plane InGaN/GaN multiple quantum well LEDs grown on r-plane sapphire

Non-polar a-plane InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs) with different thicknesses and periods of InGaN wells are prepared and characterized. Non-polar a-plane LEDs are grown directly on r-plane sapphire by metalorganic chemical vapor deposition, and LEDs are fabricated. In the electroluminescence (EL) measurements, the relative output power increases slightly with increasing well thickness and the forward operating voltage at 20 mA increases slightly, even though the 4.2 nm thick well exhibits the best photoluminescence (PL) and x-ray diffraction (XRD) results. Although the interface quality degrades with thicker InGaN wells, the relative output power in EL measurement increases due to an increase of carrier capture rate with well thickness. With increasing periods of MQWs up to seven, the relative output power of LEDs is improved due to the increased crystal and interface quality in MQWs. Meanwhile, the forward operating voltage at 20 mA increases from 3.58 to 4.12 V because the series resistance of undoped areas increases with increasing periods of MQWs.