In Plane Gated Quantum Wire Transistors

S. W. Pang and K. K. Ko

University of Michigan, Ann Arbor, Michigan 48109-2122, USA

In-plane gated (IPG) quantum wire transistors were fabricated using dry etching in a Cl2/Ar plasma generated with an electron cyclotron resonance source. (Figure 1) The electrical characteristics of the IPG transistors were correlated with the geometrical dimensions as well as dry etch and passivation conditions. In-plane gates with the width of the channel (Wc) and the width of the gate isolation (Wg) ranging from 100 to 850 nm were studied. Good field-effect transistor characteristics with transconductances up to 52 µS (290 mS/mm) were obtained on these devices (Figure 2), and they increased with smaller Wg. At a gate-source voltage (VGS) of 2 V, the saturated drain-source current (IDSAT) increased from 68 to 153 µA as Wc increased from 440 to 800 nm. No current was measured on IPG transistors with Wc<130 nm. The quasi one-dimensional channel can be completely pinched off with VGS<-1 V. It was found that the gate leakage current decreased with a wider Wg and a deeper depth for the gate isolation. The leakage current at VGS=2 V decreased significantly from 250 to less than 0.1 nA when the etch depth increased from 320 to 440 nm. The gate leakage current and IDS were also found to increase with rf power used for etching due to additional defects generated at higher ion energy. These defects, however, can be passivated with low energy chlorine species, and reduction of the gate leakage current from 40 to 4.4 nA was observed after a 1 min Cl2 plasma passivation. (Figure 3)

Figure 1. Scanning electron micrograph of in-plane gates. The in-plane gates were etched by a Cl2/Ar plasma generated with 20% Cl2 using 50 W microwave power and 100 W rf power at 0.5 mTorr.

Figure 2. IDS vs. VDS characteristics of in plane gated quantum wire transistors with Wc=440 nm and Wg=400 nm. The channel is pinched off with a gas bias of -1 V.

Figure 3. Reduction of the gate leakage current for dry etched in plane gated quantum wire ttransistors after being passivated with low energy chlorine species for different time. All transistor were first dry etched with 200 W rf power. The Cl2 plasma for passivation was generated using 50 W microwave power at 2 mTorr.

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Last Updated: November 19, 2007

E-Mail: pang@eecs.umich.edu 

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