Disorder induced interface states and their influence on the Al/Ge nanowires Schottky devices

Simon, R. A.; Kamimura, Hanay; Berengue, Olívia M.; Leite, Edson R.; Chiquito, A. J.

doi:10.1063/1.4857035

Cited by 16 publications

(10 citation statements)

References 39 publications

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“…Similar results for different contact metals (Ti and Ni) confirm the presence of surface states, which pin the semiconductor Fermi level at the interface, making barrier height almost independent of the metal work functions [12,16].…”

supporting

confidence: 66%

“…The best fit occurred for Raman shift (cm-1 ) Even having a highly crystalline structure our samples show a certain degree of disorder, especially at the surface, leading to localized energy states [12]. In this case, the transport mechanism usually observed is the variable range hopping (VRH) originally due to Mott and described by [13] per) = Po exp (�y' (1) where po and To are constants.…”

Section: E Xperimental M Ethodsmentioning

confidence: 94%

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Synthesis and characterization of crystalline germanium nanowires grown from Ag-based catalysts

Gouveia

Kamimura

Rodrigues

et al. 2014

2014 IEEE 9th Nanotechnology Materials and Devices Conference (NMDC)

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Germanium nanowires were synthesized by vapor liquid-solid method with silver nanoparticles as metal catalyst.The morphological study shows that the nanowires consist of single crystalline germanium with diamond structure, smaller than 100nm in diameter and with long range order. The electric properties were characterized in two distinct nanowire devices' indicating hopping as the main carrier transport mechanism.Hopping distance was obtained around 4nm at 300K. The metal Ge nanowires contact presented Schottky barrier of 0.46 eV for different metals and temperatures. Therefore, even with the high crystalline quality of the nanowires the surface disorder strongly influences the electric properties.

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supporting

confidence: 66%

Section: E Xperimental M Ethodsmentioning

confidence: 94%

Synthesis and characterization of crystalline germanium nanowires grown from Ag-based catalysts

Gouveia

Kamimura

Rodrigues

et al. 2014

2014 IEEE 9th Nanotechnology Materials and Devices Conference (NMDC)

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“…This electrical behavior was modeled using the back-toback Schottky model [8] under the usual thermionic emission theory assumptions. From this model we found barrier heights ranging from 0,41 to 0,51 eV regardless the different contact metals, which can be explained by the influence of surface states in the nanostructures [8,9].…”

Section: Resultsmentioning

confidence: 99%

Synthesis, Characterization and Carrier Transport Properties of Crystalline Ge Nanowires Growth with Ag-Based Catalysts

Gouveia¹,

Kamimura²,

Rodrigues³

et al. 2014

Extended Abstracts of the 2014 International Conference on Solid State Devices and Materials

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Ge nanowires were synthesized by VLS method with silver nanoparticles as metal catalyst. The structure and composition of the Ge nanowires were investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and micro-Raman technique showing single crystalline Ge nanowires smaller than 100nm in diameter. The electric properties were characterized in two distinct nanowire devices indicating hopping as the main carrier transport mechanism and we found a Schottky barrier around 0,46 eV for different metals and temperatures.

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“…The complexity of non-Ohmic contacts therefore makes comprehensive modelling of the ZnO nanowires difficult. One model which has been used successfully in the past to model non-Ohmic conduction treats both metal/semiconductor interfaces as Schottky diodes [218,219,220,221,222,223,224]. When metal comes into contact with a semiconductor, a Schottky barrier typically forms at the interface [202].…”

Section: Nanowire-metal Contacts and Schottky Barrier Modellingmentioning

confidence: 99%

“…While there are several ways of modelling back-to-back Schottky diodes, several of these rely on temperature-dependent measurements. In this chapter, we make use of the current density model first developed by Chiquito et al [218], and later used/adapted by others [219,220,221,222,223,224]. Diode measurements of nanowire devices are taken with no gate voltage applied, and the cross-sectional area of the nanowire is then ascertained using SEM.…”

Section: Nanowire-metal Contacts and Schottky Barrier Modellingmentioning

confidence: 99%

ZnO nanowires and their application in field-effect transistors

Burke-Govey¹

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<p>ZnO nanowires have shown great promise as a semiconducting material for a variety of different electronic applications at the nanoscale, and can be easily synthesised at low temperatures using the hydrothermal growth method. However, efforts to reliably produce field-effect transistors (FETs) using ZnO nanowires have been hampered by excessive charge carriers, requiring high temperature annealing (≥400°C) at the expense of the low-temperature synthesis before field dependence is achieved. This thesis presents hydrothermally synthesised ZnO nanowires which can effectively be used as FETs in dry and liquid environments without requiring any annealing or post-growth processing. The role of polyethylenimine (PEI) in the hydrothermal growth of vertical ZnO nanowires is thoroughly investigated. PEI is a polymer used to increase the aspect ratio of ZnO nanowires, but the molecular weight of the polymer and interactions with other growth precursors are often overlooked. Using 4 mM of PEI(MW = 1300 g/mol) results in hierarchical nanowires, consisting of large primary nanowires which abruptly terminate in thinner secondary nanowires. The secondary nanowires, with lengths of up to 10 m and diameters below 50 nm, are synthesised during a PEI-mediated secondary growth phase, where Zn-PEI complexes continue to provide Zn²⁺ ions after the bulk of the precursors have been exhausted. The PEI-mediated synthesis of hierarchical nanowires is used to fabricate FETs by laterally growing intersecting networks of nanowires from spaced pairs of ZnO/Ti films, which have been patterned on SiO₂/Si device substrates. All of these FETs show marked field dependence between VG = -10 V to 10 V, despite being used without annealing. Typical on-off ratios are between 10³ - 10⁵, with threshold voltages between -7.5 V to 5 V. This is a significant result, as the majority of ZnO nanowire FETs reported in the literature require high temperature annealing. Persistent photoconductivity measurements indicate that surface states on the nanowires contribute to the intrinsic field dependence of the devices. Hierarchical nanowires are also synthesised by modular primary and secondary hydrothermal growths. FETs fabricated using these hierarchical nanowires show less field dependence than PEI-mediated hierarchical nanowires, with limited function ality when used in air. The best FET measured in air operates with an on-off ratio of 10⁴ and a threshold voltage of ~ 0 V. Devices which are field-independent in air can be reliably gated by measuring the FETs in a wet environment, using de-ionised water as a dielectric. A back-gated wet FET operates with an on-off ratio of 105 and a threshold voltage of ~ 8 V. Top-gated wet FETs operate with on-off ratios within 103 - 104, and threshold voltages within 0.4 - 0.9 V. These devices also have significantly low subthreshold swings, on the order of 80 mV/decade. FETs are fabricated by contacting individual ZnO nanowires using electron-beam lithography, although only one vertical ZnO nanowire shows field dependence, with an on-off ratio of 10⁴ and a threshold voltage of -7 V. A PEI-mediated hierarchical nanowire is also contacted and shows field dependence, with an on-off ratio of 10² and a threshold voltage of -6 V. The poor on-off ratio is caused by high leakage currents of the device. The contacted nanowires undergo dissolution over time, disappearing from the substrates after 8 months, and also exhibit a conducting-to-insulating transition over 48 hours. This transition can be temporarily reversed by exposure to an electron beam. Neither of these effects are reported in the literature, and their causes are speculated on. Finally, the thesis concludes with proposals for future work to further the advances made here.</p>

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Disorder induced interface states and their influence on the Al/Ge nanowires Schottky devices

Abstract: Fermi level depinning in metal/Ge Schottky junction for metal source/drain Ge metal-oxide-semiconductor fieldeffect-transistor application J. Appl. Phys. 105, 023702 (2009)

Cited by 16 publications

References 39 publications

Synthesis and characterization of crystalline germanium nanowires grown from Ag-based catalysts

Synthesis and characterization of crystalline germanium nanowires grown from Ag-based catalysts

Synthesis, Characterization and Carrier Transport Properties of Crystalline Ge Nanowires Growth with Ag-Based Catalysts

ZnO nanowires and their application in field-effect transistors

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