Oscillatory Rate of Excess Carrier Capture into Quantum Wells of the AlGaAs/GaAs Heterostructures

Resumo

Excess carrier capture into quantum wells (QWs) of undoped AlGaAs/GaAs and modulation-doped n-AlGaAs/GaAs heterostructures has been investigated by means of photoluminescence spectroscopy. The oscillatory dependence of the photoluminescence (PL) intensity on the quantum well width caused by the resonant capture of carriers into the well has been confirmed for structures of both types. Dependences of the integral PL intensity on temperature and optical excitation density in structures with different (resonant and oscillation minimum) capture conditions have been examined. It is demonstrated that, in undoped structures, these dependences are identical at the resonant and weak capture, whereas, in doped structures, the capture efficiency strongly affects their behavior. In doped structures with weak capture, the dependence of the PL intensity on the excitation density is linear, while, in resonant structures, it is superlinear due to the growth of the hole capture rate with increasing excitation. The shift of the transition energy observed in resonant doped structures with increasing excitation is explained by accumulation of the positive charge resulting from the difference between the electron and hole capture rates. The hole capture times at the oscillation maximum and oscillation minimum have been found to be ~15 and 800 ps, respectively.