AVS 52nd International Symposium
    Electronic Materials and Processing Monday Sessions
       Session EM+NS-MoM

Invited Paper EM+NS-MoM5
MOCVD Growth of Al-rich AlGaN Alloys:  Materials for Deep-UV Emitters

Monday, October 31, 2005, 9:40 am, Room 310

Session: Novel Approaches in Wide Bandgap Semiconductors
Presenter: A.A. Allerman, Sandia National Laboratories
Authors: A.A. Allerman, Sandia National Laboratories
M.H. Crawford, Sandia National Laboratories
S.R. Lee, Sandia National Laboratories
D.M. Follstaedt, Sandia National Laboratories
P.P. Provencio, Sandia National Laboratories
K.H.A. Bogart, Sandia National Laboratories
A.J. Fischer, Sandia National Laboratories
Correspondent: Click to Email
Solid-state light sources emitting at wavelengths less than 300nm would enable technological advances in many areas such as fluorescence-based biological agent detection, non-line-of-sight (NLOS) communications, water purification, and industrial processing.  Emitters achieving such emission wavelengths have been fabricated using, almost exclusively, Al-rich alloys of AlGaN.  However the growth of Al-rich AlGaN alloys, and especially AlN, has proven problematic owing to their extreme sensitivity to growth conditions in addition to the lack of a native substrate.  Even though AlN substrates are being developed commercially, nearly all LEDs emitting in the deep UV are grown on sapphire substrates.  Typical LED structures start with an AlN buffer layer which establishes much of the basic crystal structure for the device.  The AlN layer typically exhibits threading-dislocation densities exceeding 1x10@super 10@cm@super -2@ and will experience stress-induced cracking when the layer exceeds approximately 1µm in thickness.  In this presentation, we will describe a method for AlN film growth that produces threading-dislocation densities less than 5x10@super 9@cm@super -2@.  This method involves manipulation of growth conditions following initial film nucleation and has been used to grow crack-free AlN films exceeding 3µm in thickness.  Using these AlN films as template layers, we produced Si-doped AlGaN films (with ~50-70% AlN mole fractions) that have improved electron mobilities and higher doping efficiencies.  These improvements suggest a reduced level of compensation in the AlGaN film due to reductions in dislocation density.  The presentation will also include the performance of LEDs emitting in the deep UV (<300nm) that have been fabricated with lower dislocation density AlN-AlGaN films.  Sandia is a multiprogram laboratory operated by Sandia Corporation, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-ACO4-94AL85000.  This work is also supported by DARPA under the SUVOS program managed by LTC J. Carrano.