Observation of suppressed radiative recombination in single quantum well p-i-n photodiodes

We have measured electroluminescence (EL) spectra of GaAs/InGaAs and AlGaAs/GaAs single quantum well (QW) p-i-n photodiodes at temperatures between 200 and 300 K and forward biases close to the open circuit voltage. Integrated EL spectra vary like eq(V/nkT) with an ideality factor n = 1.05 +/- 0.05 over five decades, indicating purely radiative processes. The spectra are calibrated into absolute units enabling comparison to be made with the predictions of a theoretical model. For each temperature and bias we calculate the EL spectrum and radiative current expected in the detailed balance limit, integrating the theoretical emission spectrum over the surface of the device, in order to establish the quasi-Fermi potential separation, Delta phi(f), in the QW and, where possible, in the host material. For the GaAs/InGaAs cell we are able to model emission from the QW and the host material simultaneously. We find that, in all cases, the QW emission is overestimated by theory if it is assumed that Delta phi(f) = V. QW emission corresponds instead 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 fitted 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.