Material Properties of GaN in the Context of Electron Devices

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. Virginia Commonwealth University, P.O. Box 843072, Richmond, USA 23284-3072 *

Permanent address: Dept. Material Science, University of Lecce, Lecce Italy

2. Department of Physics, Case Western Reserve University, Cleveland, OH 44106 3. Montpellier University II, 34095 Montpellier CEDEX 5 France 4. Kansas State University, Manhattan, Kansas 66506-2601 5. University of Michigan, Ann Arbor, MI 48109-2122 6. University of Illinois, Chicago, IL 60607-7053

G 1.2 Mat. Res. Soc. Syrup. Proc. Vol. 537 © 1999 Materials Research Society

particulary in modulation doped FETs. For example, electric field caused by polarization effects can increase or decrease interfacial free carrier concentrations. As in the case of quantum wells, the literature interpretation of polarization effects in devices has so far been lumped into piezoelectric effects.18.19

Despite highly imperfect material, device performance in both emitters/detectors, and the microwave amplifiers has been truly outstanding. If the defects causing premature breakdown were reduced/eliminated, one would wonder whether it would be wrong at all to attempt to develop power/switching devices with large hold voltages and current handling capabilities. In this paper, performance advantages of nitrides in vertical high power devices will be visited along with the topical topic of polarization issues. Transport Properties as Pertained to Electronic Devices Transport properties of, namely n-type, GaN and to some extent its related binaries and alloys have been calculated and experimentally investigated. There are a few noteworthy features, among which are the high peak and saturation electron velocity in GaN that does not degrade with doping, and temperature nearly as much when compared to conventional compound semiconductors. Likewise, the low field mobility does not degrade with field as fast due to the large LO phonon energy. Very intriguing are the measured low field mobilities in modulation doped structures which are nearly twice as large as the predicted polar optical phonon limited mobility at room temperature. The optimistic view could be that certain scattering mechanisms are mitigated in such structures and that the bulk low field mobility in GaN at room temperature could be as high as some 2000 cm2VsS. If so, this would pave the way for much coveted very low power loss in GaN based amplifiers and switches. Also important are transport properties at low temperatures. The low temperature electron mobility in modulation doped structures is above 7,000 cm2V-Is ' s, and the electron velocity increases which provide basis for a compelling argument that cooled GaN based devices utilizing electron transport should be capable of offering much enhanced performance. Whether to cool or not to cool a given semiconductor device must be decided following an overall power/size optimization scheme of all the components that include the power supplies, supporting circuitry, and heat dissipation related hardware. Such optimization schemes often lead to suggestions that the system

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