Quantum Transport and Sub-Band Structure of Modulation-Doped GaAs/AlAs Core–Superlattice Nanowires

Abstract

Modulation-doped III-V semiconductor nanowire (NW) heterostructures have recently emerged as promising candidates to host high-mobility electron channels for future high-frequency, low-energy transistor technologies. The one-dimensional geometry of NWs also makes them attractive for studying quantum confinement effects. Here, we report correlated investigations into the discrete electronic sub-band structure of confined electrons in the channel of Si δ-doped GaAs-GaAs/AlAs core-superlattice NW heterostructures and the associated signatures in low-temperature transport. On the basis of accurate structural and dopant analysis using scanning transmission electron microscopy and atom probe tomography, we calculated the sub-band structure of electrons confined in the NW core and employ a labeling system inspired by atomic orbital notation. Electron transport measurements on top-gated NW transistors at cryogenic temperatures revealed signatures consistent with the depopulation of the quasi-one-dimensional sub-bands, as well as confinement in zero-dimensional-like states due to an impurity-defined background disorder potential. These findings are instructive toward reaching the ballistic transport regime in GaAs-AlGaAs based NW systems.

Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties

“…By adapting a transmission probability of T(E) = 0.11 we find that the simulated conductance follows closely the traces observed in the experimental data, at least for the lowest 1D states observed near pinch-off. The lower than unity transmission probability is not surprising, given the significant scattering in the NW and the relatively long channel length (Lch = 175 nm) which prevent observation of ideal ballistic transport [7,9,10,48,49,52]. Based on the observed transmission probability and the channel length we estimate the electron mean free path (MFP) e to about 76 nm in our 25-nm thin InAs NWs.…”

“…Lowering the temperature further to 4K clearly intensifies the step-structure due to reduced thermal broadening, however, the step features are superimposed by additional Coulomb blockade-like resonances. Such behavior is typical at very low temperature where random background potential induces quantum dot-like states [49,50] that are weakly coupled to the 1D propagating modes as the thermal energy of the charge carriers is reduced [10,48].…”

“…To further elaborate the 1D-transport properties and correlate the distinct step-like features to the underlying subband structure, we plot in Fig. 5 In analogy to our previous investigations of 1D-confined GaAs NWs [10,48], we computed the mode density M(E) for each subband spacing by self-consistently solving the Schrödinger-Poisson equations using the Hartree solver nextnano++ [51], shown in the Supporting Information (Fig. S4).…”

Measuring Three-Dimensional Strain and Structural Defects in a Single InGaAs Nanowire Using Coherent X-ray Multiangle Bragg Projection Ptychography

“…In particular, there is a strong correlation between the density of stacking defects and mobility in III-As nanowires. 12,13 Comparing high resolution transmission electron microscopy (TEM) images of free standing nanowires with position dependent field effect mobility measurements on InAs nanowire devices, Schroer et al 12 showed that low densities of stacking faults localize electrons, leading to transport characteristics consistent with quantum dot formation even in devices with low resistance Ohmic contacts.…”

“…Irber et al 13 later showed that diffusive quantum transport in quasi 1-D sub-bands can be observed in modulation doped GaAs nanowires even in the presence of stacking faults, but as the stacking fault density increases, quantum features are washed out due to increased scattering. It is also well established that crystal phase switching between wurtzite (WZ) and zinc blende (ZB) polytypes, which exhibit a type II band alignment, 14 leads to the formation of quantum dots that act as single photon emitters.…”