Device Processing for GaN High Power Electronics
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Device Processing for GaN High Power Electronics S.J. Pearton(1), X.A. Cao(1), H. Cho(1), K.P. Lee(1), C. Monier(1), F. Ren(2), G. Dang(2), A.P. Zhang(2), W. Johnson(2), J.R. LaRoche(2), B.P. Gila(1), C.R. Abernathy(1), R.J. Shul(3), A.G. Baca(3), J. Han(3), J.-I. Chyi(4) and J.M. Van Hove(5) (1)
Department of Materials Science and Engineering University of Florida, Gainesville, FL 32611, USA (2)
Department of Chemical Engineering University of Florida, Gainesville, FL 32611, USA
(3)
Sandia National Laboratories Albuquerque, NM 87185, USA
(4)
National Central University Chung-Li 32054, Taiwan (5)
SVT Associates Eden Prairie, MN 55344, USA ABSTRACT Recent advances in developing process modules for GaN power devices are reviewed. These processes include damage removal in dry etched n- and p-GaN, implant doping and isolation, novel gate dielectrics, improved Schottky and ohmic contacts and deep via etching of SiC for hybrid GaN/SiC structures.
INTRODUCTION GaN device research is now shifting from photonics to electronics with the commercialization of laser diodes. GaN electronic devices are attractive for high voltage, high temperature applications, including microwave power sources, power switches and communication systems.(1) Very impressive progress has been achieved in AlGaN/GaN heterostructure field effect transistors (HFETs) in a relatively short time.(2-6) Over the past year or so, there have also been demonstrations of AlGaN/GaN heterojunction bipolar transistors (HBTs)(7), GaN Metal-Oxide Semiconductor Field Effect Transistors (MOSFETs)(8) and AlGaN power rectifiers (both Schottky and p-i-n versions.(9) With these new devices come demands for edge and surface termination techniques, gate dielectrics and more exacting requirements for minimizing disruption to the surface via thermal or energetic ion-driven processes. An example of the difference in sensitivity to dry etching of photonic and electronic devices is shown in Figure 1. In a typical laser or light-emitting diode, a mesa is formed by dry etching in order to contact the n-side of the junction. In this case, residual etch damage (which is n-type in character) is actually beneficial in improving the ohmic contact resistance by increasing the n-type doping level. By sharp contrast, in an HBT structure, the base mesa terminates on a pGaN layer. In this case, residual etch damage can severely degrade the p-ohmic contact resistance. In addition, the base layer is relatively thin (1000-2000Å) and therefore a very
T7.1.1
controlled etch rate must be employed, whereas in photonic devices the n-layer is many microns thick. In this paper we will review recent progress in developing advanced process modules for GaN power devices.
Photonic devices p-ohmic
p-GaN n-ohmic
n-GaN
Al2O3 Electronic devices
E B C
n-ohmic
n+-GaN
p-ohmic
n+-AlGaN
p-GaN
n--GaN n+-GaN
Al2O3 Figure 1. Schematics of prototypical photonic (top) and electronic (bottom) devices.
RESULTS AND DISCUSSION (a) Implantation Doping. Table I summarizes the maximum achievable doping
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