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industry  epitaxy


The stainless steel UHV growth chamber (left) and computerized electronic control system (right) of the prototype Meaglow reactor housed at Lakehead University


Butcher is willing to offer some insights into the pioneering deposition process. He explains that the high pressures associated with migration enhanced afterglow cause the high-energy plasma species, which are also present in MBE, to be largely converted into active species with lower energies. “High energy bombardment encourages N-face growth,” adds Butcher. “By avoiding such conditions, using pre- dominantly lower energy species, we have been able to grow Ga-face material at 630 °C directly on nitrided sapphire.”


Examples of success to date include GaN and InN films with a very low surface roughness. Atomic force microscopy scans on a 200 nm-thick GaN film revealed a root-mean-square (RMS) surface roughness as low as 0.24 nm. “We’ve also seen atomic terracing for InN grown at 470 °C. This has a 0.10 nm RMS surface roughness.” Crystal quality of both these films is very good, according to X-ray diffraction measurements. For the GaN film, engineers at Meaglow have recorded


(0002) ω-2θ XRD reflections with a full-width half- maximum as low as 223 arcsec, and corresponding values for the InN layer of 290 arcsec.


Standing out from the crowd Butcher’s interest in low temperature nitride growth can be traced back to his days as a PhD student in the early 1990s when he worked in the group of the late Trevor Tansley from Sydney’s Macquarie University, Australia. “When [Shuji] Nakamura first demonstrated his blue GaInN/GaN LEDs, huge resources from Japan, America and Europe were diverted into MOCVD growth of GaN,” reminisces Butcher. “Trevor had the foresight not to try


and compete with the larger groups overseas. Our group, who had been active in nitrides a good ten years before then, took a different route, concentrating on the low temperature growth of nitrides.”


Working in partnership with colleagues Bing Zhou and Xin Li, Butcher constructed a low-temperature film growth system using laser-induced CVD (LICVD). This included a remote plasma microwave source that Butcher developed. “However, later on I dropped the laser system out of the development as the uniformity using LICVD was too problematic.”


Butcher’s career briefly headed into new directions: He worked for Pacific Solar (now CSG Solar AG) from 1995 until 1997, while he finished his PhD; and for two years after that he was employed by the Australian Nuclear Science and Technology Organisation. However, he was still an Honorary Research Associate at Macquarie University, and in 1999 he was able to return to full-time research at this institution, after his and Tansley’s work caught the attention of Colin Wood from the US Office of Naval Research. Wood was able to fund Butcher’s research.


During the middle of the last decade, Butcher started to think how it would be possible to exploit the low- temperature deposition technology developed at Macquarie University. This culminated in the launch of the spin-off BluGlass in 2005, a company that set itself the ambitious task of building optoelectronic devices not only on sapphire, but also on glass, an incredibly cheap substrate. According to recent announcements by Bluglass on the Australian Stock Exchange, its material’s crystal quality still needs improvement.


Above left: Migration enhanced overflow can form Ga-face GaN films with a thickness of 200 nm at 630 ºC.Atomic force microscopy reveal that the root-mean-square surface roughness of this film is 0.23 nm. Molecular terraces can be distinguished in the image.


Above right: Atomic force microscopy reveals that the InN surface has a root-mean-square roughness of 0.1 nm and features molecular terraces


38 www.compoundsemiconductor.net October 2011


As Bluglass made progress, the health of Butcher, the firm’s Chief Technology Officer, went into decline – he was diagnosed with cancer. Although he received successful treatment in 2007 and 2008, he needed a year out to recover. And as he regained his strength, he started to mull over what he should do next. “I found that I wanted to get back to science and tackle some of the fundamental problems of low-temperature growth by developing a new technique that is a generation or two beyond what I was doing before.” This dream has


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