IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Electronics Tuesday Sessions
       Session EL-TuP

Paper EL-TuP37
Recombination Properties of Heavily Doped GaAs

Tuesday, October 30, 2001, 5:30 pm, Room 134/135

Session: Electronic Materials Poster Session
Presenter: R.K. Ahrenkiel, National Renewable Energy Laboratory
Authors: R.K. Ahrenkiel, National Renewable Energy Laboratory
W. Metgzer, National Renewable Energy Laboratory
R. Ellingson, National Renewable Energy Laboratory
D.I. Lubyshev, Quantum Epitaxial Designs, Inc.
W.K. Liu, Quantum Epitaxial Designs, Inc.
Correspondent: Click to Email
Heterojunction bipolar transistors (HBTs), using GaAs as the base, have become a technology of great importance for high speed communications. The base of the high-speed GaAs transistor is carbon doped to levels between 1x10@super 19@ and 1x10@super 20@ cm@super -3@ and the electron lifetime in the base is critical to amplifier gain. The classical band-to-band Auger effect varies as the inverse square of the free-carrier concentration. We have, for the first time, directly measured this lifetime over a wide doping range, using the up-conversion method of time-resolved photoluminescence. With this method, we were able to measure carrier lifetimes as short as 100 fs. The free hole concentrations, (p), were measured by the Hall effect and the carbon concentrations by the SIMS method. The data showed that acceptor activation was nearly 100 percent, even at 78 K. Photoconductive decay and photoluminescence data show bandgap shrinkage that is attributable to impurity band formation. Our data shows that for hole concentrations larger than 1x10@super 19@ cm@super -3@, the lifetime decreases with the inverse cube of the hole density, which is indicative of a complex Auger process. The lifetime varied from about 1 ns at 1x10@super 19@ to 600 fs at 1x10@super@20 cm@super -3@. These data are compared to the theory of Takeshima and found to vary more steeply with p, even when the impurity-assisted and phonon-assisted processes are included. However, our data suggests that the latter two processes are active because of the doping dependence. These data suggest that the impurity band plays a critical role in carrier transport. The impact of the data on HBTs will be discussed.