Negative photoconductivity in semiconductor heterostructures

Literature data on negative photoconductivity in GaAs/AlGaAs modulation doped heterojunctions and InAs/AlGaSb undoped quantum wells are explained in terms of electron–hole pair generation in the large gap layer, with subsequent charge separation and majority carrier annihilation in the well. This effect can be classified in two different limits, depending on the position of the quasi-Fermi level μ in the large gap layer. The limit with μ on the conduction band corresponds to the GaAs/AsGaAs heterostructures, and we are able to reproduce quantitatively the available experimental results. We also show that the limit with μ on the middle of the gap corresponds to the InAs/AlGaSb heterostructures.