President Bush honors Cho for MBE contribution
by Michael Hatcher
Alfred Cho, one of the key researchers behind the development of MBE - now widely used in compound semiconductor manufacturing - has received the US National Medal of Technology.
Cho was awarded the medal by President Bush at a White House ceremony on July 27 in which all recipients of the 2005 and 2006 sets of awards were recognized. US Secretary of State Condoleezza Rice and Jack Marburger, Director of Office of Science and Technology Policy, also attended the event.
Having worked on MBE at Alcatel-Lucent's Bell Laboratories since 1968, Cho is widely recognized as one of the "fathers" of the technology, which has enabled the mass manufacture of complex semiconducting devices by growing them one atomic layer at a time.
"I feel I am so lucky to represent the MBE community to receive this award," Cho told compoundsemiconductor.net after the ceremony.
Jeong Kim, currently the president of Bell Labs, summed up Cho's innovation neatly: "Decades before anyone was talking about nanotechnology , Al Cho was making it a reality."
A graduate of the University of Illinois, Cho had already picked up the National Medal of Science back in 1993, just as the MBE approach to device manufacturing was about to make an impact on the commercial semiconductor scene.
Early challenges
After working on ion propulsion technology for space travel in his days at TRW in the early 1960s, Cho switched to Bell Labs in 1968, where he hooked up with John Arthur to work on GaAs.
"I wanted to combine the ion propulsion knowledge with the surface physics knowledge to form a viable new crystal growth technology - MBE," explained Cho.
"It was not easy and did seem to be a never-ending challenge."
When Cho first began his MBE odyssey, the technical hurdles would have been daunting. One day the GaAs films that he grew would be shiny, but the next day they would be hazy. Sometimes, there would be so many defects in the films that they acted simply as insulators.
Key early breakthroughs, says Cho, were his introduction of in situ monitoring using reflection high-energy electron diffraction (RHEED), and the discovery that arsenic-stabilized surfaces led to good quality, shiny, material.
Another odd phenomenon in those early days was that the AlGaAs films Cho grew in the winter were of higher quality than those made in the summer. The reason - that dry winter air contained less water vapor than warm summer air - led Cho to introduce a sample exchange air-lock system to eliminate the contamination of the chamber and its sources.
After that, it was a case of persuading device manufacturers that multi-wafer MBE machines were far more than a lab curiosity, and would be suitable for volume device production.
And so it has turned out: examples of compound semiconductor components now made in their hundreds of millions using MBE include semiconductor lasers for optical data storage and fiber-optic networks, although perhaps the biggest single application has been in GaAs-based cellular phone power amplifiers.
As IntelliEpi CEO Yung Kao told Cho, the beauty of MBE is its flexibility - it can be used for state-of-the-art nanostructure development, but also commercial IC production.
The innovations will surely continue "“ MBE has also been identified as one of the key technologies to ensure that silicon chip makers can continue to follow Moore s Law, because the technique can be used in advanced processing to deposit high-k gate dielectrics and metals.
If it wasn t for Cho's PhD thesis advisor CD Hendricks, however, things may have turned out very differently. "When I was drifting on the California coast, Professor Hendricks persuaded me to go back to school to get my PhD," Cho recalled. "I would not be standing here [at the White House] today without his teaching and guidance."
Confusingly, Cho s latest award was the 2005 version of the National Medal of Technology. According to officials, the awards have been delayed in recent years, partly because of the lengthy vetting procedure required, and partly because of the White House being otherwise distracted.
Following the combined ceremony for 2005 and 2006 medal winners, the schedule should now be back on track.
Author
Michael Hatcher is the editor of compoundsemiconductor.net and Compound Semiconductor magazine.
