High‐efficiency AlGaN deep‐UV LEDs fabricated on a‐ and m‐axis oriented c‐plane sapphire substrates

Abstract

AbstractWe demonstrated high‐efficiency 270 nm‐band AlGaN deep‐ultraviolet (DUV) light‐emitting diodes (LEDs) fabricated on 0.15° off a‐ and m‐axis oriented c‐plane (0001) sapphire substrates grown by low‐pressure metal organic chemical‐vapor deposition (LP‐MOCVD). An approximately 4.5 μm‐thick low threading dislocation density (TDD) AlN template was grown on the sapphire substrate by using an NH3 pulsed‐flow multilayer (ML) growth method. We found that atomically flat surface can be easily obtained for AlN layer grown on a‐axis oriented sample. On the other hand, a step‐bunching was observed for the surface of AlN layer grown on m‐axis oriented sample. We found, from these results, that a‐axis oriented (0001) sapphire is more suitable for obtaining a flat surface in AlN template without step‐bunching. We also found that shorter wavelength LED can be obtained by using an a‐axis oriented (0001) sapphire, because an Al incorporation in AlGaN is slightly high for the growth on a‐axis oriented (0001) sapphire. We achieved high‐efficiency AlGaN quantum well (QW) DUV LEDs on AlN templates grown on both a‐ and m‐axis oriented sapphire substrates. The peak wavelengths of the LEDs fabricated on a‐ and m‐axis oriented sapphire were 270 and 277 nm, respectively. The maximum external quantum efficiencies (EQEs) of the LEDs fabricated on a‐ and m‐axis oriented sapphire were 3.8 and 3.2%, respectively, measured under room temperature (RT) continuous wave (CW) operations. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)