Time-resolved photoluminescence spectroscopy of tunnelling processes in a bipolar AlAs/GaAs resonant-tunnelling structure
Tunnelling and recombination of electrons and holes in a double-barrier resonant-tunnelling light-emitting diode biased below the flat band are investigated using time-resolved photoluminescence (PL) spectroscopy. The quantum well (QW) photoluminescence is dominated by carriers created directly inside the well when the excitation energy is chosen higher than the absorption edge of the QW states. Only tunnelling minority carriers created in the contact regions of the diode contribute to the QW PL when exciting with photon energy below the absorption edge. A bias region of slow non-resonant tunnelling is observed when the photocreated electrons and holes are trapped in triangular potential wells outside the QW. The resulting QW PL is unexpectedly long and lasts more than 12 ns. A mixed heavy- to light-hole valence-band resonance leads to maximum QW PL intensity around 0.7 V, accompanied by the appearance of a light-hole exciton and much shorter PL decay times. Finally, the mechanisms determining the PL intensity and line-shape variation with applied bias are analysed and discussed.