Low Temperature Nitride Semiconductor Growth
October
Macquarie University hosts the premier nitride semiconductor growth laboratory in Australia. Work on the nitrides began here in the early 1980s. Our research has concentrated on the low temperature, low substrate damage growth of aluminium nitride, gallium nitride, indium nitride and their alloys. A state-of-the-art low temperature chemical vapor deposition (CVD) unit has been built for the growth of these semiconductors. The system includes an ArF excimer laser used to crack precursor gases using photolysis (laser induced CVD) and a remote microwave plasma source to supply precursor radicals, especially atomic nitrogen (remote plasma enhanced CVD). Indium nitride is also grown at Macquarie using a radio-frequency reactive sputtering unit, despite the simplicity of this method it still provides the best quality InN.
Why nitride semiconductors? Since the early 1990s the group III nitride semiconductor gallium nitride, sometimes alloyed with indium nitride and aluminum nitride, has been used to fabricate very bright blue, violet, blue-green and white light emitting diodes (LEDs). The white LEDs will replace standard light bulbs over the next few years. Laser diodes are also being developed for high density optical storage – the next generation of DVDs. In addition solar blind UV detectors and high speed high power transistor devices (HEMT and HBT) have also been developed. In less than a decade nitride semiconductors have become some of the hottest materials around.
Why low temperatures? At present best quality gallium nitride is grown above 1000o C, by a method called MOCVD, on expensive sapphire or SiC substrates. Growth at lower temperatures would allow less expensive substrate materials, such as glass, to be used. It is also important that the atomic spacing of the substrate and the nitride films should match as closely as possible to inhibit strain in the film i.e. a close lattice match is required. Sapphire and gallium nitride do not have a close lattice match, but some temperature sensitive materials, such as ZnO, have only a very small lattice mismatch with gallium nitride. By growing at lower temperatures we hope to be able to use cheaper substrates, and substrates that are closely lattice matched to GaN.
Indium Nitride Emerges. Over twenty years ago the world's purest indium nitride was grown at Macquarie University by Trevor Tansley and Cathey Foley. This record has never been equaled. Now after more than two decades in the wilderness, international interest in indium nitride is being fueled by the potential to create higher mobility (faster) high power nitride based transistor devices. The old apparatus used to create the highest mobility (fastest) indium nitride ever grown is still in existence at Macquarie University, and has recently been upgraded to attempt another Macquarie led assault on the old record. The hope here is to understand the film growth parameters to the point where high mobility material can be routinely grown at Macquarie. If this can be achieved then the University will begin to supply this material to research groups around the world on a commercial basis.
Some of the group history and achievements:
Highest mobility nitride film ever grown (1984)
Highest purity indium nitride ever grown (1984)
High quality aluminium nitride insulating films grown by LICVD (1993)
Gallium nitride with 200 cm2·V-1·s-1 carrier mobility grown at 650o C using RPE-LICVD (1996)
Highest mobility n-type gallium nitride film ever grown on glass (2000)
Ultra-high resistivity aluminium nitride grown at room temperature (2001)
Currently, we are extending our studies to include device applications of low temperature grown GaN, in the direction of heteropolar devices such as light emitting diodes grown on glass and heterojunction bipolar transistors.
Recent Funding:
We graciously acknowledge the funding recently received by us from NICOP in partnership with the U.S. Office of Naval Research. In particular we acknowledge Dr Colin Wood and Dr Jaime Freitas Jr. for their roles in this support. These funds have been instrumental in allowing the update of our low temperature metalorganic CVD growth system, and has allowed us to greatly forward our understanding of low temperature growth processes. The U.S. Office of Naval Research also provides a useful on-line semiconductor based facility - the U.S. National Compound Semiconductor Roadmap. Funding from the Australian Institute of Nuclear Science and Engineering (AINSE) has allowed us access to a Cameca 5f SIMS system for the analysis of the composition of our nitride films. Through AINSE we also have access to a DLTS facility that allows us to probe the electronic defect structure of our films.
Not least of all in this list we must thank Macquarie University, the Division of ICS and the Physics Department for their continuing support. Dr K. S. A. Butcher is particularly thankful for the support of a Macquarie University Research Fellowship (MURF).
Leonard Quintero C.I 18.424.427 (EES)
