One of the most exciting and useful developments in modern semiconductor electronics is the capability of engineering band structure, quantum phenomena, optical properties, and other useful effects by the growth of multilayer heterostructures. With the a dvent of advanced semiconductor growth techniques such as molecular beam epitaxy (MBE), much of modern compound semiconductor device development now involves quite complex and precise multi-heterojunction structures.
In MBE, metallic sources of Ga, Al, and As along with dopants Be and Si, are evaporated or sublimed from individual ovens into an ultra-high vacuum chamber and directed onto the surface of a GaAs wafer held at about 600 oC. The epitaxial growth rate is a bout one monolayer per second, and shutters in front of the various sources can be opened and closed on the time scale of monolayer growth. As a result, precisely controlled layers of GaAs and AlGaAs can be grown in single crystal form on the lattice-mat ched GaAs wafer. For example, a GaAs quantum well can be grown sandwiched between wider bandgap AlAs or AlGaAs. With the addition of an In source, InGaAs can be grown to form narrower bandgap layers. Recently we have added a second MBE chamber for gro wth of phosphides, and a third chamber for growth of nitrides.
The availability of high-quality multilayer heterostructures has led to new effects having widespread applications such as two-dimensional transport effects, quantum wells, modulation doping, delta doping, carrier and photon confinement, etc. Recently, d istributed Bragg reflectors (DBR) have been added to this collection of capabilities. Using DBRs grown by MBE we are making unusual microcavity detectors and vertical-cavity surface-emitting lasers. As a result of these capabilities of advanced crystal growth, the future for device invention and development is extremely fertile, combining electronic and photonic effects in new ways for novel applications. Clearly, future computer and communication systems will increasingly depend on high-speed electro nic and photonic devices based on these capabilities. Applications in telecommunications and data transmission are already well underway; new applications such as optical interconnects in VLSI systems are possible and are aggressively being pursued in the UT-Austin Microelectronics Research Center.
A bulk valved cracking source for arsenic with an automatic pressure control system invented here at the Universtiy of Texas at Austin. (ref. J. Vac. Sci. Technol. B 11(3) May-June 93'. U.S. Patent 5,080,870 and 5,156,815)
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