Nonuniform Vertical Charge Transport and relaxation in Quantum Well Infrared Detectors

A. G. U. Perera, V. G. Silvestrov, S. G. Matsik
Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303

H. C. Liu, M. Buchanan, Z. R. Wasilewski
Institute for Microstructural Sciences,
National Research Council, Ottawa, KIA 0R6, Canada

M. Ershov.
Department of Computer Hardware,
University of Aizu, Aizu-Wakamatsu 965-80, Japan

ABSTRACT
The temperature dependence of capacitance and AC conductance for GaAs/AlGaAs MQW structures with 4, 8, 16 and 32 wells has been studied at different bias and frequency ranges. The dominant contribution to AC conductance depends on temperature and frequency, and changes from thermally assisted tunneling through the first excited state to thermionic emission with activation energies of 100 +_ 15 meV and 170 +_ 10 meV respectively. In the temperature interval 80 K - 100 K, conductance and capacitance have two distinct regions of frequency dispersion due to tunneling and thermionic emission respectively, giving rise to two relaxation times. Above 100K, increased conductance makes electrical response of the MQW structure so fast that at frequencies up to 1 MHz relaxational properties are masked. A model based on a series circuit comprised of barrier resistance and capacitance in parallel shows results in good agreement with experimental data, indicating strong nonuniform conductance of MQW structures.