The properties of N-polar InGaN∕GaN multiquantum wells (MQWs) grown by metal-organic chemical vapor deposition were investigated. Samples grown under optimized conditions exhibited distinct quantum well related emission, smooth surfaces, and abrupt interfaces as evaluated by room temperature photoluminescence, atomic force microscopy, and x-ray diffraction. Enhanced incorporation of indium into N-polar compared to Ga-polar MQW samples was observed for MQWs simultaneously deposited onto the (0001) and (0001¯) GaN-on-sapphire base layers using trimethylindium-to-trimethylgallium-flow-ratios larger than 1.2 during growth. Necessary adjustments of the growth procedure for N polar in comparison with Ga-polar MQWs are described.

Influence of the substrate misorientation on the properties of N-polar GaN films grown by metal organic chemical vapor deposition

Influence of the substrate misorientation on the properties of N-polar GaN films grown by metal organic chemical vapor deposition

Nitrogen-and Ga-polar GaN and InGaN/GaN multiple quantum-well (MQW) films were prepared via metal organic chemical vapor deposition and evaluated via photoluminescence at reduced temperatures in order to compare their optical characteristics. While N-and Ga-polar GaN films grown at standard high temperatures were comparable in terms of photoluminescence at tested temperatures, the Npolar InGaN MQW quality was inferior to their Ga-polar counterparts, confirmed with greater enhancement in luminescence intensity from 300 to 10 K and unobservable phonon replicas at 10 K for the N-polar InGaN MQW due to the broad emission peak. Additionally performed electroluminescence studies on N-polar light-emitting diode samples indicated that the poor luminescence of the N-polar samples was not related to electric field effects. Influence of residual impurities (C and O) was strongly suggested via secondary ion mass spectroscopy, leading us to conclude that the poor luminescence properties of the N-polar InGaN MQWs were predominantly caused by the elevated residual impurity concentrations in the N-polar (In,Ga)N layers grown at low temperatures. #

Highly efficient light emitting diodes (LEDs) with peak emission wavelengths of nominally 450 nm were grown, fabricated and tested. The growth was performed by metal organic chemical vapour deposition. The LEDs were grown on c ‐plane (0001) bulk GaN substrates and fabricated into broad‐area devices with active area 0.01 cm2. Considerations were made to improve extraction efficiency, including transparent contacts, suspended mirror‐less packaging and encapsulation in a truncated pyramid optic. These factors resulted in LEDs with high peak external quantum efficiency and reduced efficiency droop. The output power and external quantum efficiency at 20 mA were 38.5 mW and 68.9%. At 100 mA, they were 170 mW and 60.9%. White LEDs were fabricated by application of a yellow phosphor to the blue LEDs. The white LED luminous flux and efficacy at 20 mA was 9.6 lm and 128 lm/W. The chromaticity coordinates and correlated colour temperature were (0.348 K, 0.378 K) and 4998 K. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)