CHAMPAIGN, Ill. -- A semiconductor oxidation process developed at the University of Illinois a decade ago has important new applications in the fabrication of advanced electronic devices, including a type of semiconductor diode laser called a vertical-cavity, surface-emitting laser (VCSEL).
"The VCSEL is fast becoming one of the hottest items in the electronics industry," said Nick Holonyak Jr., the John Bardeen Professor of Electrical and Computer Engineering and Physics at the U. of I. who led the team that developed the oxide technology. "Among its many uses, the VCSEL can serve as an optical interconnect for high-speed data communication."
Unlike conventional edge-emitting laser diodes (the kind used in compact disc players and laser pointers, for example), a VCSEL's optical beam is perpendicular to the chip surface. This not only simplifies device fabrication and testing -- which lowers production costs -- it also creates smaller structures that consume less power.
"Research performed in various labs has shown that the U. of I. oxidation process makes the smallest, most efficient and highest performance VCSELs to date," Holonyak said.
The power of the process, Holonyak said, is its ability to selectively oxidize layers of aluminum gallium arsenide buried deep within the device structure, creating an insulating "collar" around a VCSEL's conducting cavity. "The oxide collar very effectively defines the electromagnetic field and confines the current within the aperture," Holonyak said. "The collar also controls the geometry of the optical beam, making it easier to couple the light into optical fibers for data transmission."
The oxidation process was discovered by accident in 1989, when Holonyak and graduate student John Dallesasse were investigating the effects of moisture degradation on crystals of aluminum gallium arsenide. By subjecting the crystals to temperatures of 400 degrees Celsius and high humidity, the researchers crossed a phase boundary where, instead of destroying the crystals, the chemistry created a smooth, solid oxide.
"Prior to our discovery, there was no known method for forming useful oxides in aluminum gallium arsenide or similar III-V materials," Holonyak said. "This was a real breakthrough in the preparation of these materials, which have been so important in the development of optoelectronic devices."
Holonyak, who is credited with the invention of the first practical light-emitting diode (LED) and the first semiconductor laser to operate in the visible spectrum, was the first graduate student of two-time Nobel laureate John Bardeen, a U. of I. professor who died in January 1991.