OPTICAL SPECTROSCOPY OF INVERTED ELECTRON POPULATIONS IN DOUBLE-BARRIER RESONANT-TUNNELING STRUCTURES

We present results of photoluminescence and electroluminescence spectroscopy carried out on GaAs/Al0.33Ga0.67As double-barrier resonant-tunnelling structures having quantum wells of either 200 or 250 angstrom width. At high bias, luminescence recombination is observed from electrons in highly excited (n > 2) quantum-well (QW) states of the structures. Analysis of the luminescence intensities shows that when the structures are biased at the fourth electron resonance, a population inversion occurs between the n = 4 and n = 3 confined electron levels. In addition, when the 250 angstrom QW structure is biased at the fifth resonance, a population inversion occurs between the n = 5 and n = 4 confined levels. We show that such population inversions are explained by a rate-equation analysis of the excited-state populations.