Bipolar charge redistribution in resonant-tunneling light-emitting diodes

Resonant-tunneling light-emitting diodes contain three regions where charges accumulate during device operation: the electron and hole accumulation layer in the emitter and collector, respectively, and the quantum well of the structure for bipolar accumulation. It is shown that charges redistribute over these regions with increasing current through the device and that the amount of redistribution depends on tunneling escape rate and hence on the thickness of the tunneling barriers. This charge redistribution is particularly pronounced at the resonances in the current-voltage characteristics. The process is clarified by electroluminescence spectroscopy on a set of resonant-tunneling light-emitting diodes with different barrier thickness. Signal intensities from the three spectral regions are compared and yield the relative majority carrier occupation of each region. A tradeoff in quantum-well versus accumulation-layer emission is observed as the tunneling escape rate increases with decreasing barrier thickness. Line-shape analysis yields free-carrier electron and hole broadening in the quantum well. Peak position analysis allows the determination of the electric field across the well region from which an accurate picture of the band bending during tunneling is obtained.