Unintentional High-Density p-Type Modulation Doping of a GaAs/AlAs Core–Multishell Nanowire

Abstract

Achieving significant doping in GaAs/AlAs core/shell nanowires (NWs) is of considerable technological importance but remains a challenge due to the amphoteric behavior of the dopant atoms. Here we show that placing a narrow GaAs quantum well in the AlAs shell effectively getters residual carbon acceptors leading to an unintentional p-type doping. Magneto-optical studies of such a GaAs/AlAs core-multishell NW reveal quantum confined emission. Theoretical calculations of NW electronic structure confirm quantum confinement of carriers at the core/shell interface due to the presence of ionized carbon acceptors in the 1 nm GaAs layer in the shell. Microphotoluminescence in high magnetic field shows a clear signature of avoided crossings of the n = 0 Landau level emission line with the n = 2 Landau level TO phonon replica. The coupling is caused by the resonant hole-phonon interaction, which points to a large two-dimensional hole density in the structure.

Magnetophotoluminescence in GaAs/AlAs core-multishell nanowires: A theoretical investigation

“…(3) depend on the fully ionized dopants, i.e., photoexcited carriers are not included here. As shown elsewhere [15,21], the symmetry and localization of n • h and n • e are strongly influenced by the level of doping, due to competing energy scales [12,21]. The linear free charge density per unit length provided by the dopants n • l,e(h) can finally be calculated from…”

“…[12]. A GaAs core of diameter 60 nm (facet to facet) is surrounded by a 3-nm/1-nm/3-nm AlAs/GaAs/AlAs multilayer and a 13-nm GaAs capping layer.…”

“…Long single-crystal defect-free cores [6,7], selective radial doping [8], and lateral overgrowth with high-quality interfaces [9] have been successfully realized. Most importantly, complex radial modulation doped heterostructures are now being engineered in coremultishell NWs [10][11][12][13]. More complex than their planar counterparts, radial heterostructures in these systems may host high-mobility electron/hole gases with an inhomogeneous localization in the section of the NW, which strongly depends on doping density and gate potentials [14][15][16].…”

Aharonov-Bohm oscillations and electron gas transitions in hexagonal core-shell nanowires with an axial magnetic field

“…Strong anisotropy-induced effects are predicted in this case, such as negative magnetoresistance in a transverse magnetic field [24] and symmetry-induced cancellation of the AB effect in hexagonal quantum rings [25]. The inhomogeneous electron gas localization was crucially exposed in the recent observation of intra-and interband excitations [23,26].…”

Electron localization and optical absorption of polygonal quantum rings

“…Such nanowires are usually grown vertically and, due to the crystallographic structure, have polygonal cross sections, most commonly hexagonal [12][13][14], but triangular [6,8,9,15], square [16,17], and dodecagonal [18] cross sections are also feasible. Sharp edges along the wires induce unique carrier localization, which leads to formation of one-dimensional (1D) channels in corner or side areas [19][20][21][22][23][24][25].…”