We investigated the magnetotransport of InAs nanowires grown by selective-area metal-organic vapor phase epitaxy. In the temperature range between 0.5 and 30 K reproducible fluctuations in the conductance upon variation in the magnetic field or the backgate voltage are observed, which are attributed to electron interference effects in small disordered conductors. From the correlation field of the magnetoconductance fluctuations the phase-coherence length l is determined. At the lowest temperatures l is found to be at least 300 nm while for temperatures exceeding 2 K a monotonous decrease in l with temperature is observed. A direct observation of the weak antilocalization effect indicating the presence of spin-orbit coupling is masked by the strong magnetoconductance fluctuations. However, by averaging the magnetoconductance over a range of gate voltages a clear peak in the magnetoconductance due to the weak antilocalization effect was resolved. By comparison of the experimental data to simulations based on a recursive two-dimensional Green's-function approach a spin-orbit scattering length of approximately 70 nm was extracted, indicating the presence of strong spin-orbit coupling.

Electrical transport properties of undoped and n-type doped InN nanowires grown by molecular beam epitaxy were studied by current-voltage and back-gate field-effect transistor measurements. The current-voltage characteristics show ohmic behavior in the temperature range between 4 and 300 K. Down to about 120 K a linear decrease in resistance with temperature is observed. The investigation of a large number of nanowires revealed for undoped as well as doped wires an approximately linear relation between the normalized conductance and diameter for wires with a diameter below 100 nm. This shows that the main conduction takes place in the tubular surface accumulation layer of the wires. In contrast, for doped wires with a diameter larger than 100 nm a quadratic dependence of conduction on the diameter was found, which is attributed to bulk conductance as the main contribution. The successful doping of the wires is confirmed by an enhanced conduction and by the results of the back-gate field-effect transistor measurements.

The low-temperature quantum transport properties of gated InN nanowires were investigated. Magneticfield-dependent as well as gate-dependent measurements of universal conductance fluctuations were performed to gain information on the phase coherence in the electron transport. We found a pronounced decrease in the variance of the conductance by about a factor of 2 in gate-dependent fluctuation measurements if a magnetic field is applied. This effect is explained by the suppression of the Cooperon channel of the electron correlation contributing to the conductance fluctuations. Despite the fact that the diameter of the nanowire is less than 100 nm a clear weak antilocalization effect is found in the averaged magnetoconductance being in strong contrast to the suppression of weak antilocalization for narrow quantum wires based on planar two-dimensional electron gases. The unexpected robustness of the weak antilocalization effect observed here is attributed to the tubular topology of the surface electron gas in InN nanowires. DOI: 10.1103/PhysRevB.80.125321 PACS number͑s͒: 73.23.Ϫb, 72.15.Rn, 73.63.Nm Semiconductor nanowires fabricated by a bottom-up approach are not only interesting for the realization of future nanoscaled devices 1,2 but also appear to be very attractive model systems to tackle fundamental questions concerning the transport in strongly confined systems. [3][4][5] In order to avoid the problem connected with carrier depletion, narrowband gap semiconductors, i.e., InAs or InN, 1,6,7 are preferred. The underlying reason is that here the Fermi-level pinning in the conduction band results in a carrier accumulation at the surface. In fact, the tubular topology of the surface electron gas opens up the possibility to observe unconventional quantum transport phenomena. 7 When the phase-coherence length l in the nanowire is comparable to its dimensions the conductance fluctuates if a magnetic field is applied or if the electron concentration is changed by means of a gate electrode. [8][9][10] These so-called universal conductance fluctuations being in the order of e 2 / h originate from the fact that in small disordered samples, electron interference effects are not averaged out. 11,12 Here, we analyzed universal conductance fluctuations to study the quantum transport properties in InN nanowires. In contrast to previous investigations 6,7,9,10 the successful preparation of a top-gate electrode allowed us to study universal conductance fluctuations not only as a function of magnetic field but also as a function of gate voltage. Since InN is a narrow band gap semiconductor, one naturally expects spinorbit coupling effects similar to the case of InAs. 13 Because this phenomena is of importance for spin electronic applications, we devoted special attention to the open question if spin-orbit coupling is present in InN nanowires. In transport measurements information on the spin-orbit coupling can be gained from the analysis of the characteristic beating pattern in Shubnikov-de Haas oscillations 14 or by study...

The low-temperature quantum transport of InN nanowires grown by plasma-assisted molecular beam epitaxy is investigated. Two sets of nanowires with diameters of 100 and 45 nm originating from two different growth runs are studied. Magnetic-field-dependent as well as gate-dependent measurements of universal conductance fluctuations are performed to gain information on the phase-coherence in the electron transport. By analyzing the correlation field and the average fluctuation amplitude a phase-coherence length of several hundred nanometers is extracted for both sets of nanowires at temperatures below 1 K. Conductance fluctuations are also observed when the Fermi wavelength is varied by applying a bias voltage to a back-gate. The results on the electron phase-coherence obtained from the gate-dependent measurements are consistent with the findings from the magnetic field dependent measurements. A considerable damping of the fluctuation amplitude by ensemble averaging is achieved by connecting nanowires in parallel. The suppression of the fluctuation amplitude is studied systematically by measuring samples with different numbers of nanowires. By utilizing the damping of the conductance fluctuations by connecting nanowires in parallel in combination with an averaging over the gate voltage, weak localization effects are resolved. For both sets of nanowires a clear evidence of the weak antilocalization is found, which indicates the presence of spin-orbit coupling. For the spin-orbit scattering length lso values in the order of 100 nm are extracted.

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