Morphology Of GaAs Nanowires Research Articles

N-type doping and morphology of GaAs nanowires in Aerotaxy

Controlled doping in semiconductor nanowires modifies their electrical and optical properties, which are important for high efficiency optoelectronic devices. We have grown n-type (Sn) doped GaAs nanowires in Aerotaxy, a new continuous gas phase mass production technique. The morphology of Sn doped nanowires is found to be a strong function of dopant, tetraethyltin to trimethylgallium flow ratio, Au–Ga–Sn alloying, and nanowire growth temperatures. High temperature and high flow ratios result in low morphological quality nanowires and in parasitic growth on the wire base and surface. Alloying and growth temperatures of 400 °C and 530 °C, respectively, resulted in good morphological quality nanowires for a flow ratio of TESn to TMGa up to 2.25 × 10−3. The wires are pure zinc-blende for all investigated growth conditions, whereas nanowires grown by metal-organic vapor phase epitaxy with the same growth conditions are usually mainly Wurtzite. The growth rate of the doped wires is found to be dependent more on the TESn flow fraction than on alloying and nanowire growth temperatures. Our photoluminescence measurements, supported by four-point probe resistivity measurements, reveal that the carrier concentration in the doped wires varies only slightly (1–3) × 1019 cm−3 with TESn flow fraction and both alloying and growth temperatures, indicating that good morphological quality wires with high carrier density can be grown with low TESn flow. Carrier concentrations lower than 1019 cm−3 can be grown by further reducing the flow fraction of TESn, which may give better morphology wires.

Effect of carbon tetrabromide on the morphology of GaAs nanowires

Carbon is a commonly used p-type dopant in planar III–V semiconductors, however its usein nanowire (NW) growth has been much less reported. In this work we show that themorphology of gold assisted GaAs NWs can be strongly modified by the presence ofCBr4 vapor during growth by metalorganic vapor phase epitaxy. GaAs NWs were grownunder conditions which result in strong tapering and lateral growth at low growthtemperatures by the use of triethylgallium (TEGa) instead of the more usual precursor,trimethylgallium (TMGa). Under these conditions, NWs grown in the presence ofCBr4 exhibithigher axial and lower radial growth rates, and negligible tapering compared with NWs grown in the absenceof CBr4 under the same conditions. We attribute this primarily to the suppression of the 2d growth rate byCBr4, which enhances the axial growth rate of the nanowires. NWs grown withCBr4 show stacking-fault-free zincblende structure, while the NWs grown withoutCBr4 show a high density of stacking faults. This work underlines the striking effects whichprecursor chemistry can have on nanowire morphology.

N-Type Doping of Vapor-Liquid-Solid Grown GaAs Nanowires.

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.