IWN 2010 conference report
colleagues from UCSB, the computational scientist Chris Van de Walle. He offered a new insight into an old topic, the source of yellow luminescence from carbon impurities. In addition, he described recent efforts to computationally quantify the strength of direct Auger recombination and a newly suggested process - phonon-assisted Auger. Both of these processes have a potentially important role to play in LED droop.
Delegates were also treated to an insightful presentation by Eva Monroy from CEA Grenoble, France of MBE grown inter sub-band (ISB) detectors, which included impressive TEM images. Detector results included operation well into the near IR region at 1.5 µm, the first observation of ISB absorption covering the entire mid-IR range from 1.5 to 10 µm and a demonstration of ISB absorption in the far IR at 9 meV. The audience was clearly impressed by efforts that not only married state-of- the-art growth, TEM and quantum mechanical sophistication, but also provided a glimpse into the possible future of III-Nitrides.
An update of activities at the start-up Nitek was provided by Vinod Adivarahan. He revealed that the University of South Carolina spin-off, Nitek, has produced pixelated single chip LEDs operating at 280 nm with 53 mW output and hybrid/multi-chip versions with a 233 mW output at room temperature. These power levels are suitable for sterilization, UV curing and biological detection applications.
Nitride transistors Tomas Palacios from MIT provided further evidence for the increased diversity of the III-Nitride field. In an invited talk he argued that GaN is an ideal transistor for mm- and sub-mm wave applications, before backing up his claim with a description of transistors with an fT and an fmax
of 225 GHz of 300 GHz, and an outline of pathways to
terahertz frequencies. Palacios then set the stage for parallel sessions later that week, which focused on the rapidly emerging “low hanging fruit” that is the GaN-on- silicon power electronics market. This should be a significant percentage of the well established $ 20-40 billion silicon power device market.
Another scientist accepting the invitation to speak at the conference was Masaaki Kuzuhara from University of Fukui, Japan, who also spoke about nitride transistors. He detailed the high-temperature operation of AlGaN channeled transistors with aluminum concentrations in excess of 50 percent. These outperformed variants with a GaN channel at high temperature, opening up yet another transistor market for III-Nitrides.
Enrique Calleja Pardo from UP Madrid, Spain delivered a brilliant overview of the now well-understood mechanisms for nano-rod nucleation and growth. Pardo said that this field is “fully matured”, and backed up this claim by
showcasing the research of H. Sekiguchi and his co- workers (see Appl. Phys. Lett. 96 231104 (2010)), which details the fabrication and characterization of a full color range of nano-rod-based LEDs and many other equally impressive devices. After the opening two days of invited sessions delegates were presented with a mind-numbing smörgåsbord of choices stretching out over two days of parallel sessions. Words cannot do justice to the number of choices available.
The statistics gives a flavor, however - 385 talks and 240 posters in two days that spanned epitaxial growth; bulk crystal growth; optical, electronic and magnetic properties; device processing and fabrication technologies; defect characterization and structural analysis; theory and simulation; nanostructures; light emitting devices; electron transport devices; sensors and MEMS; plus a newly added session in photovoltaics and energy harvesting. This new session included a score of talks on photovoltaics and solar-induced water splitting.
IWNS facts and figures
The International Workshop on Nitride Semiconductors 2010 was held in Tampa, Florida, from 19 to 24 September. Attendance at the meeting exceeded the previous IWN (2008) in Montreux by almost 15 percent, with 793 delegates making their way there from all over the world. 305 delegates were from North America, 255 from Asia and 204 from Europe. Following in the footsteps on previous IWN meetings, the conference started with two days of invited plenary talks, followed by two days of parallel sessions, before concluding with a mix of two plenary talks, late news, and reviews of the workshops. The traditional workshop themes, such as those of epitaxy, RF transistors and nanostructures sessions, were added to this time around, thanks to the introduction of sessions on power switching transistors, RF systems, and photovoltaics and energy harvesting.
Figure 1.
Example of an inter-subband detector and quantum well design
presented by Eva Monroy from CEA Grenoble, France. Structures covering the near, mid and far IR regions were
demonstrated
November / December 2010
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