Growth of Inclined GaAs Nanowires by Molecular Beam Epitaxy: Theory and Experiment

The growth of inclined GaAs nanowires (NWs) during molecular beam epitaxy (MBE) on the rotating substrates is studied. The growth model provides explicitly the NW length as a function of radius, supersaturations, diffusion lengths and the tilt angle. Growth experiments are carried out on the GaAs(211)A and GaAs(111)B substrates. It is found that 20° inclined NWs are two times longer in average, which is explained by a larger impingement rate on their sidewalls. We find that the effective diffusion length at 550°C amounts to 12 nm for the surface adatoms and is more than 5,000 nm for the sidewall adatoms. Supersaturations of surface and sidewall adatoms are also estimated. The obtained results show the importance of sidewall adatoms in the MBE growth of NWs, neglected in a number of earlier studies

Photovoltaic Properties of p-Doped GaAs Nanowire Arrays Grown on n-Type GaAs(111)B Substrate

We report on the molecular beam epitaxy growth of Au-assisted GaAs p-type-doped NW arrays on the n-type GaAs(111)B substrate and their photovoltaic properties. The samples are grown at different substrate temperature within the range from 520 to 580 °C. It is shown that the dependence of conversion efficiency on the substrate temperature has a maximum at the substrate temperature of 550 °C. For the best sample, the conversion efficiency of 1.65% and the fill factor of 25% are obtained

GaAs nanoscale membranes: prospects for seamless integration of III–Vs on silicon

The growth of compound semiconductors on silicon has been widely sought after for decades, but reliable methods for defect-free combination of these materials have remained elusive. Recently, interconnected GaAs nanoscale membranes have been used as templates for the scalable integration of nanowire networks on III-V substrates. Here, we demonstrate how GaAs nanoscale membranes can be seamlessly integrated on silicon by controlling the density of nuclei in the initial stages of growth. We also correlate the absence or presence of defects with the existence of a single or multiple nucleation regime for the single membranes. Certain defects exhibit well-differentiated spectroscopic features that we identify with cathodoluminescence and micro-photoluminescence techniques. Overall, this work presents a new approach for the seamless integration of compound semiconductors on silicon

Composition-dependent interfacial abruptness in Au-catalyzed Si<inf>1- x</inf>Ge<inf>x</inf>/Si/Si<inf>1- x</inf>Ge<inf>x</inf> nanowire heterostructures

As MOSFETs are scaled down, power dissipation remains the most challenging bottleneck for nanoelectronic devices. To circumvent this challenge, alternative devices such as tunnel field effect transistors are potential candidates, where the carriers are injected by a much less energetically costly quantum band to band tunneling mechanism. In this context, axial nanowire heterointerfaces with well-controlled interfacial abruptness offer an ideal structure. We demonstrate here the effect of tuning the Ge concentration in a Si1-xGex part of the nanowire on the Si/Si1-xGex and Si1-xGex/Si interfacial abruptness in axial Si-Si1-xGex nanowire heterostructures grown by the Au-catalyzed vapor-liquid-solid method. The two heterointerfaces are always asymmetric irrespective of the Ge concentration or nanowire diameter. For a fixed diameter, the value of interface abruptness decreases with increasing the Ge content for the Si/Si1-xGex interface but shows no strong Ge dependence at the Si1-xGex/Si interface where it features a linear correlation with the nanowire diameter. To rationalize these findings, a kinetic model for the layer-by-layer growth of nanowire heterostructures from a ternary Au-Ge-Si alloy is established that predicts a discrepancy in Ge concentration in the layer and the catalyst droplet. The Ge concentration in each layer is predicted to be dependent on the composition of the preceding layer. The most abrupt heterointerface (μ5 nm) is achieved by growing Si1-xGex with x = 0.85 on Si in a 25 nm diameter nanowire