Thursday, June 17, 2010

News and Views: Nature Nanotechnology

A. M. Ionescu
Nature Nanotechnology, vol. 5, iss. 3, pp. 178 – 179, March 2010

Figure (a) A junction FET is turned on in the (strong) inversion condition, when a channel of minority carriers is formed just under the gate, and junction barriers to their flow are reduced. The off state of the junction FET corresponds to high junction barriers and the suppression of the inversion channel. The horizontal red line shows the bottom of the depletion region, and the slanted red lines indicate the limits of the depletion region controlled by the gate. (b) In contrast, the on state of a junctionless FET is obtained in 'flat band' conditions, with majority carriers travelling through a highly doped film. The device (which requires a thin-film silicon-on-insulator substrate) turns off when the gate-controlled depletion extends over the whole film. Both devices operate with the source grounded and a positive potential applied to the drain. Vt denotes the threshold voltage (positive for the n-type devices). Similar descriptions apply to the operation of complementary p-type FETs. Blue and red colours depict electron and hole doping respectively, with a darker colour indicating heavier doping. The white regions correspond to the depletion regions, and the green colour represents the gate oxide.

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