Two-dimensional modeling of etched strained-silicon quantum wires

Abstract

We present two-dimensional simulations of different types of strained-silicon quantum wires obtained by selective etching on silicon germanium heterostructures. Such structures are promising both for emerging ballistic devices in silicon compatible technology and for innovative nanoscale field-effect transistors. Numerical modeling has been performed with a procedure designed to solve the Poisson–Schrödinger equation for electrons and holes, that takes into account the effect of strain on the band structure, conduction band anisotropy, and the effect of states at the exposed surfaces. We show that the simulations provide insights into the capability to control the wire via an external gate voltage, and into the dependence of wire properties on geometry and surface states.

Conductance Quantization in Schottky-gated Si/SiGe Quantum Point Contacts

“…By EBL and lift-off we patterned a 5/30nm-thick Ti/Au 100nm-wide finger gate crossing the central constriction and folding along the etched surfaces of the constriction; the electric field imposed by the gate on the lateral walls is screened by the surface states so that in this configuration the gate varies the carrier concentration without changing the width of the QPC. [3] At T=450mK the leakage from the Schottky gate (active area less than 0.1x0.16µm 2 ) to the 2DEG was negligible (leakage current I GATE <0.2 pA) in the -2V to +1V gate voltage range. This large available working range enabled a full control of electronic transport through the QPC from conduction to depletion.…”

“…Recent simulations of etched strained-silicon quantum wires with metal gates predicted a large 1D subband separation and capability of the gates in controlling the wire conductance. 40 Challenged by these promising results we adopted for the etched QPC a gating geometry similar to that considered in Ref. 40.…”

Conductance quantization in etchedSi∕SiGequantum point contacts

“…40 Challenged by these promising results we adopted for the etched QPC a gating geometry similar to that considered in Ref. 40.…”

“…40 Challenged by these promising results we adopted for the etched QPC a gating geometry similar to that considered in Ref. 40. A 5 / 30-nm-thick titanium/gold gate was patterned by EBL and lift off in the shape of a 100-nm-wide finger gate crossing the etched double bend.…”

“…Also, the surface states completely screen the electric field imposed by the gate on the lateral walls. 40 As a consequence, the gate varies the carrier concentration without affecting the width of the quantum point contact. Therefore, in our devices we can follow the effect of depleting the 1D channel at fixed modeenergy separation.…”