NONUNIFORM VERTICAL CHARGE-TRANSPORT AND RELAXATION IN QUANTUM-WELL INFRARED DETECTORS

The temperature dependence of capacitance and ac conductance for GaAs/ AlGaAs multiquantum well (MQW) structures with 4, 8, 16, and 32 wells hai been studied at different bias and frequency ranges. The dominant contribution to ac conductance depends on temperature and frequency, a nd 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 80-100 K, conductance and capacitance have two distinct regions of frequency di spersion due to tunneling and thermionic emission respectively, giving rise to two relaxation times. Above 100 K, increased conductance make s electrical response of the MQW structure so fast that at frequencies up to 1 MHz relaxational properties are masked. A model based on a se ries circuit comprised of barrier resistance and capacitance in parall el shows results in good agreement with experimental data, indicating strong nonuniform conductance of MQW structures. (C) 1998 American Ins titute of Physics. [S0021-8979(98)02802-3].