Electronic transport and band structures of GaAs/AlAs nanostructures superlattices for near-infrared detection

摘要

We report here the theoretical calculations of band structures E(d_1), E(k_z, k_p) and effective mass along the growth axis and in the plane of GaAs/Al_xGa_(1-x)As superlattices, in the envelope function formalism. The effect of valence band offset, well thickness and temperature on the band structures, has been also studied. Our results show that a transition from indirect to direct band gap in (GaAs)_m/(AlAs)_4 takes place between m = 5 and 6 monolayers at room temperature. Samples (GaAs)_9/ (AlAs)_4 and GaAs(d_1 = 10 nm)/Al_(0.15)Ga_(0.85)As(d_2 = 15 -nm) have a direct band gap of 1.747 eV at room temperature and 1.546 eV at T=30 mK, respectively. Their corresponding cutoff wavelengths are located in the near infrared region. We have interpreted the photolumines-cence measurements of Ledentsov et al. in GaAs(d_1 = 2.52 nm)/AlAs (d_1 = 1.16 nm) and the oscillations in the magnetoresistance observed by Kawamura et al. in GaAs/Al_(0.15)Ga_(0.85)As superlattice. In the later, the existence of discrete quantized levels along the growth direction z indicates extremely low interactions between adjacent wells leading to the use in parallel transport. The position of Fermi level predicts that this sample exhibits n-type conductivity. These results were compared and discussed with the available data in the literature and can be used as a guide for the design of infrared nanostructured detectors.