Topic: Atomic Layer Epitaxy of III-V Nitride Semiconductors at Low Temperatures
Speaker: Dr. Neeraj Nepal, U.S. Naval Research Laboratory, Washington DC
Date & Time: Thursday, November 7, 2013, 1:00 PM
Place: Room 140 VMC (Chambers Hall)
The III-V nitride semiconductor family has been recognized as important for various device applications. Over the last 20-25 years, significant research attention has lead to successful technologies, especially in the area of light emitters, which exploit the direct, tunable bandgap of these materials. Technologies based on electric polarization, piezoelectricity, and high breakdown field properties involve more-complex structures growth. Such structures begin to challenge the abilities of conventional growth approaches. In this seminar, I present the synthesis of III-nitride semiconductors by atomic layer epitaxy (ALE) where we find growth temperatures for high-quality crystalline layers are less than half of those needed for conventional growth methods.
Atomic layer deposition (ALD) is a pulsed growth method in which the precursors for growth are introduced in a sequence of gas pulses on top of an inert carrier gas flow. ALE is simply ALD at temperatures that are sufficient to promote surface diffusion processes that allow either homo- or hetero-epitaxial growth. With proper surface preparations, high quality, wurtzitic AlN is grown at 500 °C . These thin films (~36 nm) demonstrated smooth surfaces (~0.7 nm rms roughness for 10x10 μm2 scan area) and a (0002) peak rocking curve of width 670 arc-sec. Similar results are demonstrated for GaN films grown between 350 and 450°C. For InN, two growth regimes were defined. One between 175 and 185°C, in which a new cubic phase of InN was realized, and a second regime between 220 and 260°C for which quality wurtzitic materials were grown . Finally, initial efforts to grow ternaries of InAlN, and AlGaN were conducted using a digital alloying approach where quality, crystalline ternaries were realized over the entire stoichiometric range. The ALE is also used to demonstrate epitaxial growth of III-nitride/graphene heterostructures for the first time . These early results suggest great potential for ALE growth of III-N semiconductors, which can be used to design and grow different novel materials.
Research Laboratory (NRL), Washington DC. He received his M.S. from Tribhuwan University, Kathmandu, Nepal in 1997. He received his PhD degree in physics from Kansas State University in December 2006. He was a National Research Council (NRC) PDF at North Carolina State University before joining NRL in 2010.
During his PhD, Neeraj characterized III-nitride semiconductors and photonic structures. As a NRC fellow researcher sponsored by the US Army Research Office, he worked on metal organic chemical vapor deposition growth, characterization, and fabrication/testing of GaMnN-based diluted magnetic semiconductors and InGaN/GaN-based light-emitting devices. Currently, he is working on atomic layer deposition/epitaxy of high-k oxide and III-nitride semiconductors. He has published over 50 peer reviewed and several conference proceeding articles in the area of wide-bandgap semiconductors growths, characterizations and devices processing/testing. He is interested in the growth and characterization of new materials and their applications.
Refreshments will be served at 12:45 PM