The influence of atmosphere on the performance of pure-phase WZ and ZB InAs nanowire transistors

Abstract

Abstract. We compare the characteristics of phase-pure MOCVD grown ZB and WZ InAs nanowire transistors in several atmospheres: air, dry pure N 2 and O 2 , and N 2 bubbled through liquid H 2 O and alcohols to identify whether phase-related structural/surface differences affect their response. Both WZ and ZB give poor gate characteristics in dry state. Adsorption of polar species reduces off-current by 2 − 3 orders of magnitude, increases on-off ratio and significantly reduces sub-threshold slope. The key difference is the greater sensitivity of WZ to low adsorbate level. We attribute this to facet structure and its influence on the separation between conduction electrons and surface adsorption sites. We highlight the important role adsorbed species play in nanowire device characterisation. WZ is commonly thought superior to ZB in InAs nanowire transistors. We show this is an artefact of the moderate humidity found in ambient laboratory conditions: WZ and ZB perform equally poorly in the dry gas limit yet equally well in the wet gas limit. We also highlight the vital role density-lowering disorder has in improving gate characteristics, be it stacking faults in mixed-phase WZ or surface adsorbates in pure-phase nanowires.

Exploring the band structure of Wurtzite InAs nanowires using photocurrent spectroscopy

“…Assuming an electron mobility of 210 cm 2 .V -1 .s -1 (measured in similarly synthesized samples 20 ), one can estimate that the carrier density in the nanowire to be n3x10 17 cm -3 which is also consistent with Ref. 21. Photocurrent spectra were obtained by choosing a constant current and measuring the change in the bias voltage as the laser is tuned over a wavelength range.…”

High-Throughput Electrical Characterization of Nanomaterials from Room to Cryogenic Temperatures

“…Table 2 summarizes the calculated parameters for the seven multiplexed nanowires. While data points are too few for statistical comparison, it is a useful demonstration that nanowires can be successfully integrated with the multiplexer without any reduction in quality, since parameters compare favorably to nonmultiplexed WZ nanowires, 69 which showed V t = −7.4 V, on/off ratio = 3.4 dec, SS = 2320 mV dec −1 , n = 4.7 × 10 17 cm −3 , and μ FE = 340 cm 2 V s −1 . These measurements were performed at room temperature, which accounts for the lower mobility and higher SS 71 compared to our devices.…”

Conductometric Sensing with Individual InAs Nanowires

“…On the one hand, our results are consistent with the hypothesis of a reduced carrier density in InAs NWs in the presence of air and other adsorbates, observed by Du et al The resistance of our nanowires in dry air is in fact quite higher with respect to the behavior in vacuum (see Appendix B). Ullah et al [47] also demonstrated that the adsorption of polar species, such as H 2 O and alcohols, leads to a decrease in the carrier density in the InAs channel and a decrease in the drain-source current at zero bias. The net effect observed by these authors upon exposure to N 2 or ethanol was a reduction of the drain-source current: this is consistent with our experimental outcomes.…”

“…The mentioned studies [46,47] were performed in an inert atmosphere or in a vacuum: as claimed in the same studies, inert gases do not interact at all with the surface of InAs NWs, and their effect on the sensor behavior is equivalent to the vacuum conditions. Instead, the same does not occur if the sensor is operated in air, a more appropriate environment for testing the sensor in operating conditions is closer to real life.…”

“…Recently, nanowire-based sensing applications have gained enormous interest: InAs NWs, both individual and in array configuration, are considered as promising building blocks for the realization of gas sensors due to their easy growth mechanism, to the high value of the electron mobility and to the likely presence of a surface accumulation layer, which makes them particularly sensitive to the surface state dynamics and the environment [30,43,44,45]. Seminal studies demonstrated their exceptional suitability for humidity and organic vapor detection in an inert atmosphere (either Nitrogen or Helium): while these conditions are far from real applications, key insight on molecule-surface interactions was achieved [46,47,48]. Offermans et al investigated gas sensing with vertical arrays of nanowires, reporting an impressive response towards concentrations of NO 2 in N 2 at room temperature below 100 ppb [30].…”