The photoconductivity of p-i-n GaInNAs/GaAs multiple quantum well (MQW) mesa structures is investigated. When illuminated with photons at energy greater than the GaAs bandgap, a number of oscillations are observed in the current-voltage I-V characteristics. The amplitude and position of theoscillations is shown to depend upon the temperature, as well as upon the exciting wavelength and intensity. Due to the absence of the oscillations inthe dark I-V and at temperatures above T=200 K, we explain them in terms of photogenerated electrons escaping from quantum wells via tunnelling or thermionic emission.
Magnetic fields up to B = 11T were applied parallel to the planes of the QWs. A small voltage shift in the position of the oscillations was observed, proportional to the magnetic field intensity and dependent upon the temperature. Calculation of the Landau level energy separation (16 meV) agrees with the observed experimental data. Magneto-tunnelling spectroscopy probes in detail the nature of band- or impurity-like states responsible for resonancesin first and second subbands, observing the I-V plot in dark condition and under illumination. The field-dependence of the amplitude of the oscillation peaks in I-V has the characteristic form of a quantum mechanical admixing effect. This enhancement is also probably due to the hole recombination with majority electrons tunnelling in the N-related states of the quantum wells. (C) 2011 Elsevier B.V. All rights reserved.