Temperature-dependent study of the quasi-Fermi level separation in double quantum well P-I-N structures

We have developed a method which allows us to measure calibrated electrolum inescence (EL) spectra from quantum well (QW) structures at moderate forwar d biases. This method has been successfully applied for the first time to a symmetric double QW (DQW) p-i-n diodes in the AlGaAs/GaAs system at tempera tures between 200 and 295 K. We have measured the EL signal from both QW an d a theoretical model has been used to extract the quasi-Fermi level separa tion (Delta(phi F)) in the QWs and thus the n . p product of the excess ele ctron and hole pairs. We have made several significant observations: (1) bo th Delta(phi F) decrease relative to the applied bias (V-app) with increasi ng temperature. (2) Delta(phi F) is not the same in both wells in contradic tion with the assumption of the detailed balance theory. (3) At lower tempe ratures the quantum well Delta(phi F), show a dependence on the separation between the two QWs. (C) 2000 Elsevier Science B.V. All rights reserved.