Luminous Efficiency of Axial In_xGa_1–xN/GaN Nanowire Heterostructures: Interplay of Polarization and Surface Potentials

Abstract

Using continuum elasticity theory and an eight-band k·p formalism, we study the electronic properties of GaN nanowires with axial InxGa1-xN insertions. The three-dimensional strain distribution in these insertions and the resulting distribution of the polarization fields are fully taken into account. In addition, we consider the presence of a surface potential originating from Fermi level pinning at the sidewall surfaces of the nanowires. Our simulations reveal an in-plane spatial separation of electrons and holes in the case of weak piezoelectric potentials, which correspond to an In content and layer thickness required for emission in the blue and violet spectral range. These results explain the quenching of the photoluminescence intensity experimentally observed for short emission wavelengths. We devise and discuss strategies to overcome this problem.

Long-lived excitons in GaN/AlN nanowire heterostructures

“…This result is in agreement with calculations by Rigutti et al [51]. (GaN/AlGaN NW heterostructures with AlGaN shell) and Rivera et al [52] (GaN/AlGaN NW heterostructures without shell), and in the same line that the calculations of Marquardt et al [53] for InGaN/GaN NW heterostructures. Therefore, in addition to the polarization-induced vertical separation of electron and holes, the 3D geometry of the nanodisks leads to a radial separation of carriers, which explains the delay of the radiative recombination with respect to the quantum well case.…”

Sub-meV linewidth in GaN nanowire ensembles: Absence of surface excitons due to the field ionization of donors

“…For example, they modify the radiative decay rate of excitons [8,17] and possibly enhance the coupling between * corfdir@pdi-berlin.de free and bound excitons with profound consequences for the exciton decay dynamics [18,19]. In (In,Ga)N/GaN nanowire heterostructures, the interplay between the polarization and surface potentials may lead to a radial separation of electron and holes, resulting in a dramatic decrease of the internal quantum efficiency in the blue spectral range [20].…”

Impact of individual dopants on the electronic properties of axial In<inf>x</inf>Ga<inf>1&#x2212;x</inf>N/GaN nanowire heterostructures

“…We have recently discussed the influence of surface potentials arising from unintentional doping and Fermi level pinning on the electronic properties of axial In x Ga 1−x N/GaN nanowire (NW) heterostructures and identified a nontrivial interplay of surface and polarization potentials [6]. While this study provided a qualitative explanation for the experimentally observed reduction of photoluminescence (PL) intensity for low In contents or thin In x Ga 1−x N layers, we have assumed a homogeneous charge density arising from unintentional ntype doping here.…”

“…The recombination energy obtained when assuming a homogeneous doping charge density, as used in Ref. [6], is indicated as a solid red line. Additionally, the case of an ideal, doping-free NW is indicated with a black dashed line.…”