The thermoelectric and physical properties of superlattices consisting of modulation doped Ge quantum wells inside Si 1Ày Ge y barriers are presented, which demonstrate enhancements in the thermoelectric figure of merit, ZT, and power factor at room temperature over bulk Ge, Si 1Ày Ge y , and Si/Ge superlattice materials. Mobility spectrum analysis along with low temperature measurements indicate that the high power factors are dominated by the high electrical conductivity from the modulation doping. Comparison of the results with modelling using the Boltzmann transport equation with scattering parameters obtained from Monte Carlo techniques indicates that a high threading dislocation density is also limiting the performance. The analysis suggests routes to higher thermoelectric performance at room temperature from Si-based materials that can be fabricated using micro-and nano-fabrication techniques. V C 2013 AIP Publishing LLC.

precursors, [4] doping proves challenging for solution-synthesized MC nanostructures. [5] Recently, post-synthesis halide treatment of nanocrystals in solution has been developed which involves switching halogens for long chain surfactant molecules absorbed on the surface. [2,6] In fact, sorption of halogens can be realized as part of a one-pot synthesis using metal halide precursors. [7] Although this strategy was initially developed for passivation of MC quantum dots against oxidation, [2,6,7] annealing or hot pressing halogen-coated nanoparticles allows halides to diffuse into the MC lattice and substitute for chalcogenide anions. [8] However, controlling doping levels is not straightforward and such methods can introduce rather high halide concentrations in small nanocrystals leading to reduced electrical conductivity. [8b] Hence exerting control over dopant concentration without sacrificing electrical performance is imperative.Thermoelectrics realize direct interconversion between thermal and electric energy, thus providing an important route An aqueous solution method is developed for the facile synthesis of Cl-containing SnSe nanoparticles in 10 g quantities per batch. The particle size and Cl concentration of the nanoparticles can be efficiently tuned as a function of reaction duration. Hot pressing produces n-type Cl-doped SnSe nanostructured compacts with thermoelectric power factors optimized via control of Cl dopant concentration. This approach, combining an energy-efficient solution synthesis with hot pressing, provides a simple, rapid, and low-cost route to high performance n-type SnSe thermoelectric materials.Doping plays a vital role in modifying the electronic properties of semiconductors and is pivotal for (opto)electronics, [1] photovoltaics (PV), [2] and thermoelectrics. [3] Metal chalcogenides (MCs) form a diversity of functional materials well-suited to such applications. Halogen doping in MCs has proven effective to realize n-type conducting behavior and tune carrier concentrations. [2][3][4] Enhanced thermoelectric and PV performance can result. [2][3][4] While halogens can be readily doped into bulk MCs by high-temperature synthesis using metal halide

Cross-plane thermoelectric transport in p-type La0.67Sr0.33MnO3/LaMnO3 oxide metal/semiconductor superlattices J.A study of the impact of dislocations on the thermoelectric properties of quantum wells in the Si/SiGe materials system

A prototype particle tracking telescope has been constructed using Timepix and Medipix ASIC hybrid pixel assemblies as the six sensing planes. Each telescope plane consisted of one 1.4 cm 2 assembly, providing a 256×256 array of 55 µm square pixels. The telescope achieved a pointing resolution of 2.3 µm at the position of the device under test. During a beam test in 2009 the telescope was used to evaluate in detail the performance of two Timepix hybrid pixel assemblies; a standard planar 300 µm thick sensor, and 285 µm thick double sided 3D sensor. This paper describes a detailed charge calibration study of the pixel devices, which allows the true charge to be extracted, and reports on measurements of the charge collection characteristics and Landau distributions. The planar sensor achieved a best resolution of 4.0 ± 0.1 µm for angled tracks, and resolutions of between 4.4 and 11 µm for perpendicular tracks, depending on the applied bias voltage. The double sided 3D sensor, which has significantly less charge sharing, was found to have an optimal resolution of 9.0 ± 0.1 µm for angled tracks, and a resolution of 16.0 ± 0.2 µm for perpendicular tracks. Based on these studies it is concluded that the Timepix ASIC shows an excellent performance when used as a device for charged particle tracking.2

The thermal emissivity of crystalline silicon photovoltaic (PV) solar cells plays a role in determining the operating temperature of a solar cell. To elucidate the physical origin of thermal emissivity, we have made an experimental measurement of the full radiative spectrum of the crystalline silicon (c-Si) solar cell, which includes both absorption in the ultraviolet to near-infrared range and emission in the mid-infrared. Using optical modelling, we have identified the origin of radiative emissivity in both encapsulated and unencapsulated solar cells. We find that both encapsulated and unencapsulated c-Si solar cells are good radiative emitters but achieve this through different effects. The emissivity of an unencapsulated c-Si solar cell is determined to be 75% in the MIR range, and is dominated by free-carrier emission in the highly doped emitter and back surface field layers; both effects are greatly augmented through the enhanced optical outcoupling arising from the front surface texture. An encapsulated glass-covered cell has an average emissivity around 90% on the MIR, and dips to 70% at 10 µm and is dominated by the emissivity of the cover glass. These findings serve to illustrate the opportunity for optimising the emissivity of c-Si based collectors, either in conventional c-Si PV modules where high emissivity and low-temperature operation is desirable, or in hybrid PV-thermal collectors where low emissivity enables a higher thermal output to be achieved