Multifunctional Devices and Logic Gates With Undoped Silicon Nanowires Massimo Mongillo,1, a) Panayotis Spathis,1, b) Georgios Katsaros,1 Pascal Gentile,2 and Silvano De Franceschi1 1)
SPSMS/LaTEQS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, 38054 Grenoble Cedex 9, France 2) SP2M/SINAPS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, 38054 Grenoble Cedex 9, France
arXiv:1208.1465v1 [cond-mat.mes-hall] 7 Aug 2012
We report on the electronic transport properties of multiple-gate devices fabricated from undoped silicon nanowires. Understanding and control of the relevant transport mechanisms was achieved by means of local electrostatic gating and temperature dependent measurements. The roles of the source/drain contacts and of the silicon channel could be independently evaluated and tuned. Wrap gates surrounding the silicide-silicon contact interfaces were proved to be eﬀective in inducing a full suppression of the contact Schottky barriers, thereby enabling carrier injection down to liquid-helium temperature. By independently tuning the eﬀective Schottky barrier heights, a variety of reconﬁgurable device functionalities could be obtained. In particular, the same nanowire device could be conﬁgured to work as a Schottky barrier transistor, a Schottky diode or a p-n diode with tunable polarities. This versatility was eventually exploited to realize a NAND logic gate with gain well above one. Nanometer-scale electronic devices fabricated from silicon nanowires (SiNWs) are drawing signiﬁcant attention in view of their potential application in electronics1 , optoelectronics2 and biochemical sensing3,4 . The transport properties and the functionality of such electronic devices are usually controlled by doping. In most cases, the incorporation of doping impurities in SiNWs is obtained in-situ during nanowire growth5 , but a precise control over their spatial distribution6,7 and their activation8 has not been achieved yet. Doping control becomes a particularly critical issue when the characteristic device size approaches the nanometer scale, i.e. comparable to the typical distance between dopants for standard doping levels (1017 - 1019 cm−3 ). In this limit, device performances can depend on only a few dopants9,10 , and be extremely sensitive to their precise locations, leading to a signiﬁcant device-to-device variability. The main obstacle coming from the use of undoped nanowires lies in the diﬃculty to form low-resistance contacts due to the unavoidable presence of a Schottky barrier (SB)11 at the metal-silicon interface. Therefore, understanding and controlling the properties of electrical contacts to SiNWs is of fundamental importance12 . Here, we investigate the properties of metal-silicide contacts to undoped SiNWs, and we study the possibility to obtain largely-tunable contact resistances through a combination of two fabrication processes: a controlled silicidation of the metal-SiNW contacts and the fabrication of local gate electrodes wrapped around each silicon-silicide interface. We demonstrate that contact resistances can be largely suppressed with gate voltages of the order of 1 V, enabling measurable carrier injection down to 4K. In addition, through local electrostatic doping of the SiNW, our approach provides the possibility to implement diﬀerent functionalities within the same SiNW device, which can work as a bipolar transistor, a Schottky diode or p-n diode with gate-tunable polarities. Finally, we provide as well an example of how two such devices could be programmed to operate as a NAND logic gate. We used undoped SiNWs grown by chemical vapor deposition via a catalytic vapor-liquid-solid method (growth details were given in an earlier work13 ). Our sample fabrication process relies on a few steps of e-beam lithography, e-beam metal deposition, and lift-oﬀ. Initially, alignment markers and ordered arrays of 500-nmwide Cr/Al (10/5 nm) gate electrodes, spaced by 500 nm, are deﬁned on top of an oxidized...
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