We report in-plane and through-plane conductivity measurements of dense YSZ films varying in thickness from 20 to 200 nm. In-plane measurements were performed on YSZ films grown on silicon wafers coated with SiO 2 or Si 3 N 4 . Micro-fabricated strips with Pt electrodes in various geometries were used to obtain conductivity as a function of temperature from 200 – 600 °C in a custom-designed micro-probe station. These films have activation energies, which vary from 0.77 to 1.09 eV. Their absolute conductivity is lower compared with other reports. Through-plane and fuel cell measurements were performed by depositing YSZ on a nitrided silicon wafer, then etching through the wafer and depositing porous platinum electrodes on both sides [6,7]. We discuss the electrochemical conduction studies in detail along with fuel cell performance and correlation with electrode microstructure.

One key challenge for silicon-based solar cells is the weak absorption of long-wavelength photons near the bandgap (1.1eV) due to the indirect bandgap of silicon. A large fraction of the AM 1.5 solar spectrum falls into a regime (0.7 μm – 1.1 μm) where silicon does not absorb light well. The capture of these long-wavelength photons imposes a particular problem to the thin-film silicon solar cells. For this reason, thin-film silicon solar cells often incorporate some forms of light trapping mechanisms.

Low-dimensional nanostructures and nano-composites may demonstrate a large enhancement of the thermoelectric figure of merit ZT, therefore measurements of their thermoelectric properties are of high interest. Techniques able to screen the thermoelectric properties of a large number of samples and also to measure the spatial distribution of thermoelectric properties in a specimen are needed. This work explores a scanning transient technique for thermoelectric characterization of thin films based on the Harman method. A one dimensional theoretical model was used to investigate the appropriate experimental setup and the effect of a scanning electrode/thermal probe contacting the top surface of the specimen. Results indicate that for micrometer thick films of ZT∼1 small current values of the order of mA and electrical contact resistance below 1 Ω are necessary to minimize the Joule heating effects and to take advantage of the Peltier effect when employing the bipolar technique. A proof of concept experiment was performed on an n-type Bi 2 Te 3 pellet used in a commercial thermoelectric device. The experiment lays out the strategy to extract the thermoelectric properties. Seebeck coefficient of −241 μV/K and thermal conductivity of 1.48 W/m.K were obtained from the transient Harman method when the data reduction model included energy losses through the wire. These results prelude the feasibility of the scanning technique on thin film samples.

We present a simple theory of diffusive phonon heat transport in silicon thin films using the Two-Temperature Model (TTM). In silicon thin films, boundary scattering reduces the lifetime and hence, the mean free path of acoustic phonons. As acoustic phonons are responsible for heat transport in silicon, the latter effect leads to a reduction in the lattice thermal conductivity. However, optical phonons are unaffected by boundary scattering. As the boundary scattering rate exceeds the inverse lifetime of acoustic phonons and the energy relaxation rate between optical and acoustic phonons, it results in an energy transfer bottleneck. The reduced lattice thermal conductivity from boundary scattering and the energy transfer bottleneck are taken into account in the TTM. We apply the TTM to find the steady temperature distribution in a 2D model of a silicon-on-insulator (SOI) device. The numerical results are in good agreement with those obtained from the more sophisticated full dispersion model of the Boltzmann Transport Equation (BTE). We apply the TTM to calculate the steady state and transient temperature distributions in a simplified 1D model of a SOI device.

Thermoelectric effects can be used for direct conversion of heat into electricity using a solid-state device. We describe novel metal/semiconductor nanostructured materials where the heat and charge transport are modified at the atomic level. Hot electron filtering using heterostructure barriers is used to break the trade off between high Seebeck coefficient and high electrical conductivity. Embedded ErAs nanoparticles are used to reduce the lattice thermal conductivity without significant effect on electrical conductivity. The thermal conductivity, electrical conductivity, and Seebeck coefficient of ErAs:InGaAlAs alloys are characterized. The measured ZT is ∼1 at high temperatures 650 K. Integrated circuit fabrication techniques are used to transfer the n- and p-type thin films onto AlN plates and power generation modules are made with hundreds of thin film elements. An output power density >1W/cm2 is demonstrated at an external temperature difference of 120K across the module. Finally, the prospect of other metal semiconductor multilayer structures based on TiN/GaN for high temperature operation will be briefly reviewed.