In situ etching for total control over axial and radial nanowire growth

We report a method using in situ etching to decouple the axial from the radial nanowire growth pathway, independent of other growth parameters. Thereby a wide range of growth parameters can be explored to improve the nanowire properties without concern of tapering or excess structural defects formed during radial growth. We demonstrate the method using etching by HCl during InP nanowire growth. The improved crystal quality of etched nanowires is indicated by strongly enhanced photoluminescence as compared to reference nanowires obtained without etching

Electron Transport in Low Dimensional Systems

This thesis consists of experimental studies of transport properties in high mobility two dimensional electron gases (2DEGs). Two material systems are used, an AlGaAs/GaAs heterojunction and a GaInAs/InP quantum well. The AlGaAs/GaAs heterojunction is used for top gating, either to additionally reduce the dimensionality of the 2DEG to observe one dimensional effects, or to explore the edge channel picture employed to describe electron transport in high magnetic fields. For the other materials system, the GaInAs/InP quantum well, a complete description of the development of a heterostructure were the highest electron mobility ever achieved in a ternary material is given. In addition, several transport effects introduced by the special qualities of the ternary semiconductor, GaInAs, such as alloy-disorder scattering and the pinning of the Fermi level in the conduction band, are discussed

Growth of p-type GaN - The role of oxygen in activation of Mg-doping

The effects of N2 and O2:N2 (1:1) as ambient gases during activation annealing of Mg as p-type doping of GaN have been investigated. The purpose was to understand the mechanisms involved and especially the impact of O2 on the resulting hole concentration and hole mobility. The addition of O2 to the ambient gas during annealing is known to be very effective in reducing the H level of the Mg-doped GaN layer, but the maximum achievable hole concentration and mobility, as determined by Hall characterization, is still higher with pure N2. The difference is explained by an in-diffusion of O to the GaN layer acting as n-dopant and thus giving rise to a compensation effect. It is found that to a large degree only the Mg-H complexes at substitutional (MgGa), i.e., the electrically active acceptor sites that provide free holes, are activated by annealing with N2 only as ambient gas, while annealing with O2:N2 (1:1) also dissociates electrically inactive Mg-H complexes resulting in much less residual H. Thus, the residual H level in relation to the Mg level after activation annealing with N2 only may provide a representative measure of the resulting free hole concentration of the Mg-doped GaN layer.This project has received funding from the ECSEL Joint Undertaking (JU) under grant agreement No 826392. The JU receives support from the European Union's Horizon 2020 research and innovation program and Austria, Belgium, Germany, Italy, Slovakia, Spain, Sweden, Norway, and Switzerland.</p

Precursor evaluation for in situ InP nanowire doping

The use of tetraethyltin (TESn) and dimethylzinc (DMZn) as in situ n- and p-dopant precursors during particle-assisted growth of InP nanowires is reported. Gate voltage dependent transport measurements demonstrate that the nanowires can be predictably synthesized as either n- or p-type. These doped nanowires can be characterized based on their electric field response and we find that n- type doping scales over a range from 10(17) to 10(19) cm(-3) with increasing input TESn dopant molar fraction. On the other hand, the p-type doping using DMZn saturates at low levels, probably related to a strong increase in nanowire growth rate with increasing DMZn molar fractions. By optimizing growth conditions with respect to tapering, axial pn-junctions exhibiting rectifying behavior were fabricated. The pn-junctions can be operated as light emitting diodes

MOVPE-grownInAs/AlAs0.16Sb0.84/InAs and InAs/AlAs0.16Sb0.84/GaSb heterostructures

We demonstrate MOVPE-growth of InAs/AlAs0.16Sb0.84/GaSb and InAs/AlAs0.16Sb0.84/InAs heterostructures of excellent quality as observed by transmission electron microscopy and x-ray diffraction 2-theta-omega and rocking curve scans with full width at half maximum routinely below 100 arcsec. Key points regarding interface control for heteroepitaxial nucleation are reviewed and the choice of suitable precursors to minimize the incorporation of C and O are discussed