We demonstrate high yield vapor-liquid-solid (VLS) growth of [100]-oriented InP nanowire arrays. The highest yield (97%) is obtained when the catalyst droplet is filled with indium prior to nanowire nucleation to the equilibrium composition during nanowire growth. Using these [100] wires as a template we can reversibly switch between a [100] and a [111] growth direction by varying the indium content of the droplet. Modeling VLS growth by a kinetic nucleation model indicates that the growth direction is governed by the liquid-vapor interface energy that is strongly affected by the indium concentration in the catalyst droplet.

We demonstrate an efficiency enhancement of an InP nanowire (NW) axial p-n junction solar cell by cleaning the NW surface. NW arrays were grown with in situ HCl etching on an InP substrate patterned by nanoimprint lithography, and the NWs surfaces were cleaned after growth by piranha etching. We find that the postgrowth piranha etching is critical for obtaining a good solar cell performance. With this procedure, a high diode rectification factor of 10(7) is obtained at ±1 V. The resulting NW solar cell exhibits an open-circuit voltage (Voc) of 0.73 V, a short-circuit current density (Jsc) of 21 mA/cm(2), and a fill factor (FF) of 0.73 at 1 sun. This yields a power conversion efficiency of up to 11.1% at 1 sun and 10.3% at 12 suns.

Rational bottom-up assembly of nanowire networks may be a way to successfully continue the miniaturization in the semiconductor industry. A generic method is developed that ensures InSb nanowires meet under the optimal angle for the formation of single-crystalline structures, which represents a promising platform for the future random access memories based on Majorana fermions.

Nanowire based solar cells have attracted great attention due to their potential for high efficiency and low device cost. Photovoltaic devices based on InP nanowires now have characteristics comparable to InP bulk solar cells. A detailed and direct correlation of the influence of growth conditions on performance is necessary to improve efficiency further. We explored the effects of the growth temperature, and of the addition of HCl during growth, on the efficiency of nanowire array based solar cell devices. By increasing HCl, the saturation dark current was reduced, and thereby the nanowire solar cell efficiency was enhanced from less than 1% to 7.6% under AM 1.5 illumination at 1 sun. At the same time, we observed that the solar cell efficiency decreased by increasing the tri-methyl-indium content, strongly suggesting that these effects are carbon related.