A. Maaßdorf , S. Gramlich, E. Richter, F. Brunner, M. Weyers, and G. Tränkle
Ferdinand-Braun-Institut für Höchstfrequenztechnik, Albert-Einstein-Straße 11, D-12489 Berlin, Germany

Published in:

J. Appl. Phys., vol. 91, no. 8, pp. 5072-5078 (2002).

Abstract:

Room-temperature photoluminescence decay time measurements in heavily doped GaAs:C-layers designed as base layers for heterojunction bipolar transistors are reported. These measurements provide access to nonequilibrium minority carrier lifetimes that determine the current gains of those devices. By systematically studying transient luminescence spactra over a wide range of excitation densities between 10¹³ and 10¹⁸ cm^-3, we demonstrate the importance of carrier trapping processes at low excitation densities. Optimized excitation conditions that achieve trap saturation but also avoid stimulated emission are found for densities of (1-3)x10¹⁷ cm^-3/pulse. Detection is limited to a spectral window well above the energy gap (beyond 1.5 eV). Values for both Auger and radiative recombination coefficients are given.

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