Determination of the quasi-Fermi-level separation in single-quantum-well p-i-n diodes

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Abstract
The radiative behavior of quantum‐well (QW) devices depends upon the quasi‐Fermi‐level separation ΔEf induced in the quantum well. We present a method of obtaining ΔEf in absolute units from the emission spectra of optically or electrically biased QWs. Emission spectra are calibrated by comparison with measurements of the limiting photocurrent. A theoretical model is then used to separate out the effects of carrier generation rate and field‐dependent QW absorption. We apply the method to the low‐temperature photoluminescence spectra of a set of single QW p‐i‐n photodiodes at different electric fields. We show that modeled emission spectra agree closely with measured spectra in flatband conditions. We also observe a field‐dependent loss in emission intensity—leading to a reduction in ΔEf of several meV—which we attribute mainly to carrier escape from the QW. The derived values for field‐dependent nonradiative efficiency are consistent with independent measurements of low‐temperature dc photocurrent, and with a simple model for thermally assisted carrier escape. We show how the method can be applied to electroluminescence spectra in order to investigate the dependence of ΔEf on applied bias.