Improvement of surface roughness and reduction of threading dislocation density in AlN/AlGaN templates on sapphire by employing trimethylaluminum pulsed supply growth

Abstract

We fabricated high-quality AlN/AlGaN templates, which are applicable to ultraviolet (UV) emitters on sapphire, by using a trimethylaluminum (TMAl) pulsed-supply growth method. We succeeded in achieving a dramatic improvement in the surface roughness of AlN/AlGaN layer by introducing a short-period pulsed supply of TMAl during the growth intervals of a 'standard' AlGaN growth regime. We speculate that the improvement in surface roughness is due to the realization of stable group III (+c) polarity by the growth of an Al-rich surface. In addition, we have found that this method is effective for reducing threading dislocation densities (TDD). The TDD was reduced from 2.9×109 to 1.1×109 cm-2 by introducing the TMAl pulsed supply growth. We fabricated a 350 nm-band InAlGaN multi-quantum well (MQW) UV lightemitting diode (LED) on an AlN/AlGaN template formed by the TMAl pulsed supply method, and obtained an output power of 1.95 mW under room temperature (RT) CW operation. The output power of the LED was increased by a factor of 1.7 by introducing the TMAl pulsed supply method. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.