The influence of the droplet composition on the vapor-liquid-solid growth of InAs nanowires on GaAs ( 1 ¯ 1 ¯ 1 ) B by metal-organic vapor phase epitaxyWe report on controlled p-type doping of GaAs nanowires grown by metal-organic vapor-phase epitaxy on ͑111͒B GaAs substrates using the vapor-liquid-solid growth mode. p-type doping of GaAs nanowires was realized by an additional diethyl zinc flow during the growth. Compared to nominally undoped structures, the current increases by more than six orders of magnitude. The transfer characteristics of fabricated nanowire metal-insulator-semiconductor field-effect transistor devices proved p-type conductivity. By adjusting the II/III ratio, controlled doping concentrations from 4.6ϫ 10 18 up to 2.3ϫ 10 19 cm −3 could be achieved at a growth temperature of 400°C. The doping concentrations were estimated from electrical conductivity measurements applied to single nanowires with different diameters. This estimation is based on a mobility versus carrier concentration model with surface depletion included.

Gallium arsenide nanowires are grown on 100 GaAs substrates, adopting the epitaxial relation and thus growing with an angle around 35 degrees off the substrate surface. These straight nanowires are irradiated with different kinds of energetic ions. Depending on the ion species and energy, downwards or upwards bending of the nanowires is observed to increase with ion fluence. In the case of upwards bending, the nanowires can be aligned towards the ion beam direction at high fluences. Defect formation (vacancies and interstitials) within the implantation cascade is identified as the key mechanism for bending. Monte Carlo simulations of the implantation are presented to substantiate the results.

Metal-insulator field-effect transistors (FETs) are fabricated using a single n-InAs nanowire (NW) with a diameter of d = 50 nm as a channel and a silicon nitride gate dielectric. The gate length and dielectric scaling behavior is experimentally studied by means of dc output-and transfer-characteristics and is modeled using the long-channel MOSFET equations. The device properties are studied for an insulating layer thickness of 20-90 nm, while the gate length is varied from 1 to 5 µm. The InAs NW FETs exhibit an excellent saturation behavior and best breakdown voltage values of V BR > 3 V. The channel current divided by diameter d of an NW reaches 3 A/mm. A maximum normalized transconductance g m /d > 2 S/mm at room temperature is routinely measured for devices with a gate length of ≤ 2 µm and a gate dielectric layer thickness of ≤ 30 nm.Index Terms-InAs nanowire (NW) field-effect transistor (FET), omega-shaped gate, silicon nitride, vapor-liquid-solid (VLS) growth.

Heterostructure n-GaAs/InGaP/p-GaAs core-multishell nanowire diodes are synthesized by metal-organic vapor-phase epitaxy. This structure allows a reproducible, selective wet etching of the individual shells and therefore a simplified contacting of single nanowire p-i-n junctions. Nanowire diodes show leakage currents in a low pA range and at a high rectification ratio of 3500 (at ±1V). Pronounced electroluminescence at 1.4 eV is measured at room temperature and gives evidence of the device quality. Photocurrent generation is demonstrated at the complete area of the nanowire p-i-n junction by scanning photocurrent microscopy. A solar-conversion efficiency of 4.7%, an open-circuit voltage of 0.5 V and a fill factor of 52% are obtained under AM 1.5G conditions. These results will guide the development of nanowire-based photonic and photovoltaic devices.

In this letter, n-type doping of GaAs nanowires grown by metal–organic vapor phase epitaxy in the vapor–liquid–solid growth mode on (111)B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations ND of GaAs nanowires are found to vary from 7 × 1017 cm-3 to 2 × 1018 cm-3. The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal–insulator-semiconductor field-effect transistor devices.