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The electronic structure and transmission coefficients of Si nanowires are calculated in a sp/sup 3/d/sup 5/s/sup */ model. The effect of wire thickness on the bandgap, conduction valley splitting, hole band splitting, effective masses, and transmission is demonstrated. Results from the sp/sup 3/d/sup 5/s/sup */ model are compared to those from a single-band effective mass model to assess the validity of the single-band effective mass model in narrow Si nanowires. The one-dimensional Brillouin zone of a Si nanowire is direct gap. The conduction band minimum can split into a quartet of energies although often two of the energies are degenerate. Conduction band valley splitting reduces the averaged mobility mass along the axis of the wire, but quantum confinement increases the transverse mass of the conduction band edge. Quantum confinement results in a large increase in the hole masses of the two highest valence bands. A single-band model performs reasonably well at calculating the effective band edges for wires as small as 1.54-nm square. A wire-substrate interface can be viewed as a heterojunction with band offsets resulting in reflection in the transmission.

We report an improved tunneling-based SRAM (TSRAM) cell design using symmetric low current density InGaAs/InAlAs/AlAs/InAs resonant-tunneling diodes (RTD's). The new design eliminates an interconnect compared to the previous record low 50 nW TSRAM cell demonstrated with asymmetric low current density RTDs and heterostructure field-effect transistors (HFETs) in our InP-based integrated process. The simplified cell has 4/spl times/ smaller area than III-V FET-only SRAM cells at the same design rule. We also investigate experimentally and theoretically the mechanism for reduced peak-to-valley current ratios for very low current density (/spl sim/1 A/cm/sup 2/) RTDs which affects TSRAM cell standby power.