The cross-plane thermal conductivity of four Si/Si 0.7 Ge 0.3 superlattices and three Si 0.84 Ge 0.16 /Si 0.76 Ge 0.24 superlattices, with periods ranging from 45 to 300 and from 100 to 200 Å, respectively, were measured over a temperature range of 50 to 320 K. For the Si/Si 0.7 Ge 0.3 superlattices, the thermal conductivity was found to decrease with a decrease in period thickness and, at a period thickness of 45 Å, it approached the alloy limit. For the Si 0.84 Ge 0.16 /Si 0.76 Ge 0.24 samples, no dependence on period thickness was found and all the data collapsed to the alloy value, indicating the dominance of alloy scattering. This difference in thermal conductivity behavior between the two superlattices was attributed to interfacial acoustic impedance mismatch, which is much larger for Si/Si 0.7 Ge 0.3 than for Si 0.84 Ge 0.16 /Si 0.76 Ge 0.24. The thermal conductivity increased slightly up to about 200 K, but was relatively independent of temperature from 200 to 320 K.

We demonstrate double quantum dots fabricated in undoped Si/SiGe heterostructures relying on a double top-gated design. Charge sensing shows that we can reliably deplete these devices to zero charge occupancy. Measurements and simulations confirm that the energetics are determined by the gate-induced electrostatic potentials. Pauli spin blockade has been observed via transport through the double dot in the two electron configuration, a critical step in performing coherent spin manipulations in Si.Comment: 4 pages, 4 figure

We have demonstrated few-electron quantum dots in Si/SiGe and InGaAs, with occupation number controllable from N = 0. These display a high degree of spatial symmetry and identifiable shell structure. Magnetospectroscopy measurements show that two Si-based devices possess a singlet N =2 ground state at low magnetic field and therefore the two-fold valley degeneracy is lifted. The valley splittings in these two devices were 120 and 270 {\mu}eV, suggesting the presence of atomically sharp interfaces in our heterostructures.Comment: 3 pages, 3 figure

Monolithically integrated active cooling is an attractive way for thermal management and temperature stabilization of microelectronic and optoelectronic devices. SiGeC can be lattice matched to Si and is a promising material for integrated coolers. SiGeC/Si superlattice structures were grown on Si substrates by molecular beam epitaxy. Thermal conductivity was measured by the 3 method. SiGeC/Si superlattice microcoolers with dimensions as small as 40ϫ40 m 2 were fabricated and characterized. Cooling by as much as 2.8 and 6.9 K was measured at 25°C and 100°C, respectively, corresponding to maximum spot cooling power densities on the order of 1000 W/cm 2 . © 2001 American Institute of Physics. ͓DOI: 10.1063/1.1356455͔Thermoelectric ͑TE͒ refrigeration in a solid-state active cooling method with high reliability. Bi 2 Te 3 -based TE coolers are widely used for cooling and temperature stabilization of microelectronic and optoelectronic devices, but their processing is a bulk technology and is incompatible with integrated circuit fabrication process. Solid-state coolers monolithically integrated with microelectronic and optoelectronic devices are an attractive way to achieve compact and efficient cooling. It can lower the cost of fabrication and packaging, and can selectively cool individual key devices instead of the whole chip. However, the thermoelectric figure of merit ͑ZT͒ is quite low for most of the semiconductors used in microelectronics and optoelectronics. This makes it difficult to get high cooling performance. Recently heterostructure thermionic and superlattice coolers have been proposed, and theoretical calculations show that large improvements in ZT can be achieved and efficient refrigeration becomes possible with coolers made of conventional semiconductor materials.

A new fabrication technique is used to produce quantum dots with read-out channels in silicon/silicon-germanium two-dimensional electron gases. The technique utilizes Schottky gates, placed on the sides of a shallow etched quantum dot, to control the electronic transport process. An adjacent quantum point contact gate is integrated to the side gates to define a read-out channel and thus allow for noninvasive detection of the electronic occupation of the quantum dot. Reproducible and stable Coulomb oscillations and the corresponding jumps in the read-out channel resistance are observed at low temperatures. The fabricated dot combined with the read-out channel represent a step towards the spin-based quantum bit in Si/SiGe heterostructures.