OBSERVATION OF SUPPRESSED RADIATIVE RECOMBINATION IN SINGLE-QUANTUM-WELL P-I-N PHOTODIODES

We have measured electroluminescence (EL) spectra of GaAs/InGaAs and A lGaAs/GaAs single quantum well (QW) p-i-n photodiodes at temperatures between 200 and 300 K and forward biases close to the open circuit vol tage. Integrated EL spectra vary like eq(V/nkT) with an ideality facto r n = 1.05 +/- 0.05 over five decades, indicating purely radiative pro cesses. The spectra are calibrated into absolute units enabling compar ison to be made with the predictions of a theoretical model. For each temperature and bias we calculate the EL spectrum and radiative curren t expected in the detailed balance limit, integrating the theoretical emission spectrum over the surface of the device, in order to establis h the quasi-Fermi potential separation, Delta phi(f), in the QW and, w here possible, in the host material. For the GaAs/InGaAs cell we are a ble to model emission from the QW and the host material simultaneously . We find that, in all cases, the QW emission is overestimated by theo ry if it is assumed that Delta phi(f) = V. QW emission corresponds ins tead to a value of Delta phi(f) which a few tens of mV less than V. In contrast, emission from the host material, where visible, is well fit ted by the model with Delta phi(f) = V at all biases and temperatures. We attribute the variation in Delta phi(f) to irreversible thermally assisted escape from the QWs. (C) 1997 American Institute of Physics.