Pulsed modulation doping of AlxGa1-xN (x>0.6) AlGaN epilayers for deep UV optoelectronic devices

We report a new approach of pulsed modulation doping (PMD) to achieve n-type doping in AlxGa1-xN (x>0.6) layers. In this approach silane flow is cyclically modulated during n-AlGaN growth which enable us to grow low dislocation density n-AlGaN templates for UV (lambda similar to 280 nm) LEDs. We observed that dislocation density for un-doped AlGaN layers on high quality AlN layers is 3.3x10(8) cm(-2). This dislocation density was increased to 2.3x10(9) cm(-2) for conventionally grown n-AlGaN layers on AlGaN templates. We were able to reduced dislocation density in n-AlGaN layers to 3.5x10(8) cm(-2) using PMD of n-AlGaN layers. The dislocation densities in these samples were studies using etch pit density (EPD) and Williamson and Hall studies. A comparative study of LED structures on conventional and PMD doped n-AlGaN showed improved performance for LED emitting at 280 nm for LED structure on PMD n-doped AlGaN layers. In this paper the details of our growth procedure, the epi-structure X-ray, AFM, and other characterizations will be presented. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim