Fabrication and characterization of a GaAs-based three-terminal nanowire junction device controlled by double Schottky wrap gates

Abstract

A three-terminal nanowire junction device controlled by double nanometer-sized Schottky wrap gates ͑WPGs͒, which control left and right branches independently, are fabricated utilizing AlGaAs/ GaAs etched nanowires and characterized experimentally. Recently, nanowires have attracted much attention for the next-generation nanodevice materials. Nanowire junctions are important building blocks for nanowire-based devices and their integrated circuits. Rich functionalities were expected theoretically in these systems due to the ballistic transport of carriers 1 and self gating. 2 Clear nonlinear characteristics have been observed in three-terminal nanowire junctions of III-V compound semiconductors 3,4 and carbon nanotubes, 5 even at room temperature. In addition, capability of their high-speed operation has been demonstrated experimentally. 4,6 Their application to logic circuits has been also intensively investigated. 7,8 In this letter, we fabricate and characterize a GaAs-based three-terminal nanowire junction device, in which two branches can be controlled independently by nanometer-sized Schottky wrap gates ͑WPGs͒, in order to control the nonlinear characteristics toward nanowire-based circuits and systems. Figure 1͑a͒ shows a scanning electron microscopy ͑SEM͒ image of a fabricated device. The device had a T-branch nanowire junction formed on an AlGaAs/ GaAs heterostructure wafer by electron beam lithography and wet chemical etching. Geometrical nanowire width W geo was 560 nm. Nanowire lengths for left and right branches were 3 m and that for a center branch was 2.6 m. Cr/ Au Schottky WPGs of 400 nm gate lengths were formed on the left and right branches. The WPG wrapped around a nanowire can squeeze effective nanowire width W eff , and onedimensional channel is formed under suitable gate voltage. 9 Measured mobility and the sheet carrier density of the unprocessed wafer at room temperature ͑RT͒ were 7100 cm 2 / V s and 7.8ϫ 10 11 cm −2 , respectively. WPGcontrolled nanowire branches of the fabricated device could operate as conventional field effect transistors, as shown in Fig. 1͑b͒. They showed good gate control characteristics and operated similarly to each other. Their threshold voltages for nanowire channel pinch off were −0.9 V. In this study, all measurements were carried out at RT. Figure 2 shows measured output voltages at the center terminal, V C , by applying voltages to the left and right terminals, V L and V R , respectively, in push-pull fashion, namely, V R =−V L . When left and right WPG voltages V GL and V GR , respectively, were kept at 0 V, V C showed bell-like curves and was always negative as shown in Fig. 2, indicated by dashed lines. We also fabricated and characterized a three-terminal device without WPGs and similar characteristic was obtained. Next, V C was measured by changing V GL while keeping V GR at 0 V. Obtained V C -V L curves are shown in Fig. 2͑a͒

Graphene‐based three‐branch nano‐junction (TBJ) logic inverter

“…Owing to the nonlinearity, the TBJ operates as AND gate by itself [2,3]. Since the nonlinear characteristic is available even at room temperature [2,4], the TBJ device has been widely investigated and has been applied to various analog and digital circuits [3,[5][6][7]. Graphene is an attractive material for the TBJ device because of the ballistic transport owing to the high carrier mobility, which is important for the nonlinear characteristic [1].…”

Boolean Logic Gates Utilizing GaAs Three-Branch Nanowire Junctions Controlled by Schottky Wrap Gates

“…As a possible mechanism occurring in a nonballistic transport regime, we considered the effect of surface potential of the nanowire. 5) We also found that the voltage transfer efficiency of the TBJ can be controlled by attaching Schottky wrap gates (WPGs) on the input branches. 5,6) This device configuration allows its operation as a conventional NOT gate.…”

“…5) We also found that the voltage transfer efficiency of the TBJ can be controlled by attaching Schottky wrap gates (WPGs) on the input branches. 5,6) This device configuration allows its operation as a conventional NOT gate. This gives us a new opportunity to implement any Boolean logic function by integrating only TBJs with identical configurations.…”

Characterization of GaAs-Based Three-Branch Nanowire Junction Devices by Light-Induced Local Conductance Modulation Method

“…A pioneering work by Xu indicates that the nonlinear characteristic appears when the TBJ is operated in the ballistic transport regime 1) . However, experimentally, it is also clearly observed at room temperature (RT) [14][15][16][17][18] where the carrier transport should be in the nonballistic transport regime. The mechanism in such a case has not been clarified yet, although several hypotheses have been introduced, including those regarding the effective mean free path extension 16) and the asymmetric channel depletion due to the surface potential [19][20][21][22][23][24][25][26] .…”

“…The III-V semiconductor nanowire surface is known to behave similarly to a metal gate because high-density surface states fix the surface Fermi level at a certain energy level. From the size dependence of the nonlinear curve 26) and its asymmetric change in the gate-controlled TBJ devices 17,25) , we suppose that this model is applicable to the nonlinear characteristic at RT. To verify the applicability of this model, the identification of the existence of the conductance domain and its portion is necessary.…”