Performance and reliability of ultraviolet-C pseudomorphic light emitting diodes on bulk AlN substrates

Abstract

Low dislocation density, epitaxial layers of Al_xGa_1–xN are grown pseudomorphically on native AlN substrates prepared from high quality, bulk crystals. In addition to low dislocation density, they are atomically smooth and can be doped n-type to obtain sheet resistances < 200 Ohms/sq/μm. These layers are used as templates for the growth of high quality multiple quantum well (MQW) structures and ultraviolet (UV) light emitting diodes (LED). The pseudomorphic growth and atomically smooth surfaces are achieved for a full device structure. Previously we have demonstrated the high optical quality of these structures through temperature dependant photoluminescence measurements and X-ray diffraction. Recently full device structures have been fabricated and packaged. These devices, with emission wavelength between 250 nm and 280 nm show linear increase in output power as a function of current up to 150 mA in thermal equilibrium. Additionally output powers up to 1.3 mW have been achieved at 258 nm at 400 mA drive current. Reliability of the devices has been measured for 1000 hours with expected lifetimes greater than 3000 hours for input currents up to 150 mA (with an average current density of approximately 150 A/cm²). (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)