Thermoelectric properties on Ge/Si1−xGex superlattices

Thermoelectric generation has been found to be a potential field which can be exploited in a wide range of applications. Presently the highest performances at room temperature have been using telluride-based devices, but these tech- nologies are not compatible with MEMs and CMOS processing. In this work Silicon and Germanium 2D superlattices have been studied using micro fabri- cated devices, which have been designed specifically to complete the thermal and electrical characterization of the different structures. Suspended 6-contact Hall bars with integrated heaters, thermometers and ohmic contacts, have been micro-fabricated to test the in-plane thermoelectric properties of p-type superlattices. The impact of quantum well thickness on the two thermoelectric figures of merit, for two heterostructures with different Ge content has been studied. On the other hand, etch mesa structures have been presented to study the cross-plane thermoelectric properties of p and n-type superlattices. In these experiments are presented: the impact of doping level on the two figures of merit, the impact of quantum well width on the two figures of merit, and the more efficient reduction of the thermal conductivity by blocking phonons with different wavelengths. The n-type results showed the highest figures of merit values reported in the literature for Te-free materials, presenting power factors of 12 mW/K2 · m, which exceeded by a factor of 3 the highest values reported in the literature. The results showed, that Si and Ge superlattices could compete with the current materials used to commercialise thermoelectric modules. In addi- tion, these materials have the advantage of being compatible with MEMs and CMOS processing, so that they could be integrated as energy harvesters to create complete autonomous sensors

Thermoelectrics, Photovoltaics and Thermal Photovoltaics for Powering ICT Devices and Systems

The conversion of heat into electricity through the thermoelectric effect and light into electricity through photovoltaic solar cells both allow useful amounts of power for a range of ICT systems from a few milli‐Watts (mW) for autonomous sensors up to kilo‐Watts (kW) for complete ICT computing or entertainment systems. Photovoltaics at the large scale can also be used to produce MW power stations suitable for the sustainable powering of high‐performance computing (HPC) and dataservers for cloud computing. This chapter provides a background to the physics of operation of both types of sustainable energy sources along with the fundamental limits of both technologies. The present performance is presented along with promising research directions to allow for a comparison of the useful power along with the limits for deployment of each approach to power ICT devices and systems. Finally, the developing field of thermal photovoltaics is reviewed, where the overall thermodynamic conversion efficiency of turning light into electricity and useful heat can be increased through the addition of thermoelectrics or heat transfer modules to a photovoltaic cell

The use of silicon-germanium superlattices for thermoelectric devices and microfabricated generators

Low dimensional structures such as superlattices have the potential to improve the thermoelectric properties of materials by engineering the scattering of phonons to reduce the thermal conductivity and therefore improve the thermeoelectric performance. Here we demonstrate the reduction in thermal conductivity in Ge/SiGe superlattices using multiple barrier engineering to scatter acoustic phonons at the key wavelengths for thermal transport. The approach allows ZT to be increased in wide quantum well superlattices through the reduction of heterointerfaces which scatter both electrons and phonons

High Efficiency Planar Geometry Germanium-on-silicon Single-photon Avalanche Diode Detectors

This paper presents the performance of 26 μm and 50 μm diameter planar Ge-on-Si single-photon avalanche diode (SPAD) detectors. The addition of germanium in these detectors extends the spectral range into the short-wave infrared (SWIR) region, beyond the capability of already well-established Si SPAD devices. There are several advantages for extending the spectral range into the SWIR region including: reduced eye-safety laser threshold, greater attainable ranges, and increased depth resolution in range finding applications, in addition to the enhanced capability to image through obscurants such as fog and smoke. The time correlated single-photon counting (TCSPC) technique has been utilized to observe record low dark count rates, below 100 kHz at a temperature of 125 K for up to a 6.6 % excess bias, for the 26 μm diameter devices. Under identical experimental conditions, in terms of excess bias and temperature, the 50 μm diameter device consistently demonstrates dark count rates a factor of 4 times greater than 26 μm diameter devices, indicating that the dark count rate is proportional to the device volume. Single-photon detection efficiencies of up to ~ 29 % were measured at a wavelength of 1310 nm at 125 K. Noise equivalent powers (NEP) down to 9.8 × 10-17 WHz-1/2 and jitters < 160 ps are obtainable, both significantly lower than previous 100 μm diameter planar geometry devices, demonstrating the potential of these devices for highly sensitive and high-speed imaging in the SWIR

3D LIDAR imaging using Ge-on-Si single–photon avalanche diode detectors

We present a scanning light detection and ranging (LIDAR) system incorporating an individual Ge-on-Si single-photon avalanche diode (SPAD) detector for depth and intensity imaging in the short-wavelength infrared region. The time-correlated single-photon counting technique was used to determine the return photon time-of-flight for target depth information. In laboratory demonstrations, depth and intensity reconstructions were made of targets at short range, using advanced image processing algorithms tailored for the analysis of single–photon time-of-flight data. These laboratory measurements were used to predict the performance of the single-photon LIDAR system at longer ranges, providing estimations that sub-milliwatt average power levels would be required for kilometer range depth measurements

Afterpulsing in Ge-on-Si single-photon avalanche diodes

In this letter, we investigate afterpulsing in 26 and 100 μm diameter planar geometry Ge-on-Si single-photon avalanche diode (SPAD) detectors, by use of the double detector gating method with a gate width of 50 ns. Ge-on-Si SPADs were found to exhibit a 1% afterpulsing probability at a delay time of 200 μs and temperature of 78 K, and 130 μs at a temperature of 150 K. These delay times were measured with an excess bias of 3.5% applied, which corresponded to a single-photon detection efficiency of 15% at 1.31 μm . We demonstrate that reducing the detector diameter can also be an effective way to restrict afterpulsing in this material system

Ge-on-Si Single Photon Avalanche Diode Detectors for LIDAR in the Short Wave Infrared

Ge-on-Si single photon avalanche diodes are used to demonstrate LIDAR in laboratory conditions. Modelling demonstrates that eye-safe kilometre range-finding is achievable at 1450nm wavelength. Afterpulsing is found to be considerably lower than commercial InGaAs/InP devices

Coupled simulation of performance of a crossed compound parabolic concentrator with solar cell

An optimal installation of a compound parabolic concentrator (CCPC) into a scalable solar thermoelectrics and photovoltaics system is desirable by applying analytical tools to improve the optical and thermal performance of a CCPC with a solar cell. In this paper, the optical and thermal performances of an isolated CCPC with solar cell are investigated by employing commercial software ‘ANSYS CFX 15.0’ with a coupled optical grey and multiphysics model. Numerical results are validated against the experimental data at various incidence angles, especially for the optical concentration ratio and optical efficiency. Results confirm that ‘ANSYS CFX’ is an effective numerical tool for determining correctly both the optical and thermal behaviour of CCPC. The very important finding is a highest temperature core in the silicon layer of solar cell which may be responsible for a solar cell to work properly. The limitation of the work is that the electric performance of the solar cell is not involved and the simulations are steady

Diseño y fabricación de tarjetas de circuito impreso con componentes empotrados

Consulta en la Biblioteca ETSI Industriales (7953)[ES] Este proyecto se trata de un estudio de investigación cuya idea comenzó a ser desarrollada algunos años atrás por Joe Fjelstad, un veterano en la industria de interconexiones de la electrónica. Joe Fjelstad, presidente de Verdant Electronics, se encarga de promover el proceso Occam, el cual se encuentra definido en su documento oficial denominado White Green Paper, y el cual va a ser la base del estudio realizado en este proyecto ya que no existe mucha más información que ésta. Por ello se puede decir que se está ante un campo totalmente nuevo e innovador.Ferre Llin, L. (2009). Diseño y fabricación de tarjetas de circuito impreso con componentes empotrados. http://hdl.handle.net/10251/34150.Archivo delegad

Modelling and Experimental Verification of a Ge/SiGe Thermoelectric Generator

Thermoelectric generators (TEG) are devices that generate electricity when a temperature gradient is created across it. Therefore these generators can be used to power micro-scaled devices by harvesting the heat that is released to the environment in different systems. This work presents the Finite Element (FE) model and experimental approaches for investigating the performance of a Ge/SiGe-based TEG. The TEG studied in this work was fabricated using a novel p- and n-type nano-fabricated 2-D Ge/SiGe superlattice grown by low-energy plasma-enhanced chemical vapour deposition (LEPECVD). A single p- and n-leg were coupled together using indium as the bonding material. Results for open and short circuit voltages are presented, using both the experimental and FE modeling approaches. An effective Seebeck voltage of 200μV/K and a maximum power density of 60μW/m2 with a temperature difference of 1.15 K were obtained for this device. The FE model was validated using an analytical method in open circuit and both results closely matched. Although the fabricated module is unoptimized at this stage, it is hoped that the FE model will be used to design an optimal and feasible TEG module in the near future, using an improved Ge/SiGe-based material