"An insight into GaN nanowires and GaN-AlN core-shell nanowire heterostructures grown by plasma-assisted molecular beam epitaxy"

Dr. Karine Hestroffer, Post-Doctoral researcher, ECE, UCSB

February 15th (Friday), 2:30pm
Engineering Science Building (ESB), Room 2001

In virtue of their defect-free characteristics, GaN nanowires (NWs) are known to be an advantageous alternative to the heteroepitaxy of 2D GaN layers. Their growth by plasma-assisted molecular beam epitaxy (PAMBE) was reported for the first time in 1997 on sapphire and in 1998 on silicon. The main originality of these NWs resides in their growth mode which is free of catalyst, induced by diffusion processes combined to a difference of incorporation rates between the NW side-walls and their top surface. Nevertheless, despite numerous studies published on their properties, the mechanisms underlying GaN NW formation (or nucleation) remained unclear for many years. In this talk, using a combination of i_n situ _grazing-incidence X-ray diffraction experiments performed at the European Synchrotron Radiation Facility and of reflection high energy electron diffraction analyses, those mechanisms are explored and related to the polarity of GaN NWs.

The second part of this talk will focus on GaN-AlN core-shell NWs. As a matter of fact, PAMBE-grown GaN NWs are typically oriented along the _c_-axis. In other words, GaN NW lateral walls are oriented perpendicularly to _c_, i.e. along nonpolar directions. Such consideration has naturally nurtured the interest in core-shell NWs, with the aim of growing non-polar nitride NW heterostructures. As a first stage towards the realization of GaN NW-based radial heterostructures, we investigate the strain state inside GaN NW cores, induced by the deposition of a single AlN shell.

About Dr. Karine Hestroffer:

Karine Hestroffer received the B.Sc. degree and M.Sc. degree in condensed matter physics and nanophysics from the University of Strasbourg, France, in 2009, and the Ph.D degree in condensed matter and beam physics from the University of Grenoble, France, in 2012. Her Ph.D. work, undertaken in the group of Dr. Bruno Daudin at the French Atomic Energy and Alternative Energy Commission (CEA) of Grenoble, dealt with the investigation of the growth by PAMBE and the characterization of GaN NWs. She recently started a post-doc in the group of Prof. Mishra. Her researches focus on the growth by PAMBE of N-polar GaN-based HEMT structures.

Hosted by: Professor Umesh Mishra, Electrical and Computer Engineering