Radial modulation doping in core–shell nanowires

Abstract

Semiconductor nanowires are potential candidates for applications in quantum information processing, Josephson junctions and field-effect transistors and provide a unique test bed for low-dimensional physical phenomena. The ability to fabricate nanowire heterostructures with atomically flat, defect-free interfaces enables energy band engineering in both axial and radial directions. The design of radial, or core-shell, nanowire heterostructures relies on energy band offsets that confine charge carriers into the core region, potentially reducing scattering from charged impurities on the nanowire surface. Key to the design of such nanoscale heterostructures is a fundamental understanding of the heterointerface properties, particularly energy band offsets and strain. The charge-transfer and confinement mechanism can be used to achieve modulation doping in core-shell structures. By selectively doping the shell, which has a larger bandgap, charge carriers are donated and confined in the core, generating a quasi-one-dimensional electron system with higher mobility. Here, we demonstrate radial modulation doping in coherently strained Ge-SixGe1-x core-shell nanowires and a technique to directly measure their valence band offset. Radial modulation doping is achieved by incorporating a B-doped layer during epitaxial shell growth. In contrast to previous work showing site-selective doping in Ge-Si core-shell nanowires, we find both an enhancement in peak hole mobility compared with undoped nanowires and observe a decoupling of electron transport in the core and shell regions. This decoupling stems from the higher carrier mobility in the core than in the shell and allows a direct measurement of the valence band offset for nanowires of various shell compositions.

Acoustic phonons and strain in core/shell nanowires

“…In particular, new terms arise in the corresponding strain and stress tensors that are absent in homogeneous NWs. We illustrate our results via the example of Ge/Si NWs, given the fact that the coherence of their interfaces has already been demonstrated experimentally [41,42]. The derived formulas for the static strain can be considered a further extension of those listed in Ref.…”

Comprehensive Theoretical and Experimental Studies on Iii-Nitrides, Doping, Nano-Structures and Leds

“…However, the purpose here is to generate high concentration carriers in wide band gap nitrides, which is otherwise difficult by directly doping the material itself, whereas the modulation doping is typically used to separate the dopant ions from the carriers in order to achieve high carrier mobility in the well, as wildly studied in arsenide or Ge/Si. 49,50 In summary, a novel strategy for efficient p-type doping was proposed to overcome the fundamental problem of high activation energy in high bandgap III-nitrides by introducing impurity resonant states in an Mg doped AlxGa1-xN/GaN superlattice structure. This structure can be used to achieve efficient nitride based optoelectronic devices, especially in the deep ultraviolet wavelength range.…”

Supersymmetric Transformations in Optical Fibers

“…Physical systems with axial symmetry present particular interest not only in quantum mechanics [31,32] but also in other branches of physics, such as acoustics and photonics. In acoustics, cylindrical ducts are of special interest for pressure wave propagation and turbocharger applications [33][34][35][36].…”