Quantum capacitance devices

Two-dimensional electron gas (2DEG) in a quantum well or inversion layer, unlike an ordinary grounded metallic plane, does not completely screen an applied transverse electric field. Owing to its Fermi degeneracy energy, a 2DEG manifests itself as a capacitor in series, whose capacitance per unit area equals CQ=me2/πℏ2, where m is the effective electron mass in the direction transverse to the quantum well. Partial penetration of an external field through a highly conducting 2DEG allows the implementation of several novel high-speed devices, including a three-terminal resonant-tunneling transistor and a gate-controlled thermionic emission transistor.

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