conference report IWN 2010
Figure 2. X-ray diffraction spectra and AFM images for MME grown InGaN
throughout the miscibility gap showing single phase materials with excellent surface
morphology, MBE derived techniques presented by Michael
Moseley from Georgia Institute of Technology
the promising nitrogen polar green LEDs reported by the Ohio State University group in the late news session and the encouragingly high hole concentration presented by student Jonathan Lowder and co-workers at Georgia Tech. Last, but by no means least, in the closing invited talk LED pioneer Hiroshi Amano pointed out that MBE and its related variants are capable of accomplishing things that other technologies struggle to achieve. While it is too early to determine if any of these new reports will manifest into manufacturable products, IWN 2010 did highlight the promise of alternative growth technologies in a field where MOCVD dominates.
Attendance was healthy, and some invited sessions were standing room only. They were not there to hear good news, however, but to wrestle with one of the weaknesses of nitride devices. The unavoidable truth is that today all InGaN photovoltaic results are abysmal single digit efficiencies. This poor showing stems from phase separation issues within InGaN that limit the practically achievable device energy bandgap to portions of the solar spectrum with minimal radiation. The upshot is low efficiencies.
One possible route to overcoming these issues was revealed in an invited talk by Christiana Honsberg from the Arizona State University. She presented some intriguing new results, attained in collaboration with student Michael Moseley from Georgia Institute of Technology, which outlined growth methods that can completely eliminate phase separation. Similar growth techniques have been used by Chris Boney’s team from the University of Houston, and have yielded respectable currents but at lower than expected voltages. Water-splitting talks highlighted challenges with surface stability against photo-electrochemical etching. The results realized to date are highly dependent on surface treatments and measurement methodology. Several speakers also pointed out that a successful photo- electrochemical process would need to include a method for separating hydrogen and oxygen. This topic was largely outside the focus of the session.
MBE: down but not out
During the IWN meeting there was an intriguing subtle undercurrent that spontaneously emerged throughout the meeting: a resurgence in promising MBE results, particularly regarding the growth of InGaN based devices. Evidence of this resurgence could be found in the talk given by Moseley from Georgia Institute of Technology, which detailed the control of phase separation throughout the entire miscibility gap using Metal Modulated Epitaxy (MME). It was also present in Chris Boney’s InGaN solar cell award winner poster, the ultra-high growth rate results from the Los Alamos National Laboratory group using their scalable ENABLE process, and also in Christina Honsberg’s descriptions of the impact MME would have on InGaN photovoltaics. What’s more, MBE featured in
46
www.compoundsemiconductor.net November / December 2010
On the last day of the conference, just like the first, conference chairs Christian Wetzel and Asif Kahn gave tribute to honorary chair, Isamu Akasaki from Meijo University, Japan, for his pioneering work and leadership in the Nitride community.
Fittingly, it was announced that
the next IWN meeting will be held on October 14-19, 2012, at Sapporo, Japan. Hiroshi Amano from Nagoya University is taking the role of executive committee chair, with Yoichi Kawakami from Kyoto University serving as program committee chair.
If the III-nitride field continues
to grow at the current rate, the famous beer gardens of Sapporo that are close to the meeting will be drained dry by hoards of thirsty “Nitridors”.
Rump sessions in Tampa
To maintain the workshop nature of IWN, the conference organizing committee added five rump sessions to the IWN meeting. These sessions, which gave the audience a chance to pose questions to a panel of invited experts, were highly successful with attendance bursting out of many rooms. Discussions were lively, and in some cases, playfully controversial. The rump sessions covered: III-N on silicon: the best of two amazing semiconductors, which focused on how the integration with silicon enables new opportunities (and challenges) for III-N semiconductors in power electronics, optoelectronics and energy
III-N challenges for RF electronics: which revolved around scaling, speed and reliability issues for pushing the ‘standard’ HEMT performance
Ideal III-nitride substrate technology: a discussion on getting the right balance between cost of the substrate and its quality, which can enhance device performance
LED IQE roadmap: from 70 percent to 90 percent, which looked at all the issues relating to increased efficiency
III-N nanowires: a debate on the fundamental issues regarding growth, doping, and novel applications.
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