This paper describes the first thermoelectric devices based on the V-VI-compounds Bi/sub 2/Te/sub 3/ and (Bi,Sb)/sub 2/Te/sub 3/ which can be manufactured by means of regular thin film technology in combination with microsystem technology. Fabrication concept, material deposition for some 10-/spl mu/m-thick layers and the properties of the deposited thermoelectric materials will be reported. First device properties for Peltier-coolers and thermogenerators will be shown as well as investigations on long term and cycling stability. Data on metal/semiconductor contact resistance were extracted form device data. Device characteristics like response time for a Peltier-cooler and power output for a thermogenerator will be compared to commercial devices

Multi-quantum-well structures of Bi2Te3 are predicted to have a high thermoelectric figure of merit ZT. Bi2Te3 thin films and Bi2Te3∕Bi2(Te0.88Se0.12)3 superlattices (SLs) were grown epitaxially by molecular beam epitaxy on BaF2 substrates with periods of 12 and 6nm, respectively. Reflection high-energy electron diffraction confirmed a layer-by-layer growth, x-ray diffraction yielded the lattice parameters and SL periods and proved epitaxial growth. The in-plane transport coefficients were measured and the thin films and SL had power factors between 28 and 35μW∕cmK2. The lattice thermal conductivity varied between 1.60W∕mK for Bi2Te3 thin films and 1.01W∕mK for a 10nm SL. The best figures of merit ZT were achieved for the SL; however, the values are slightly smaller than those in bulk materials. Thin films and superlattices were investigated in plan view and cross section by transmission electron microscopy. In the Bi2Te3 thin film and SL the dislocation density was found to be 2×1010cm−2. Bending of the SL with amplitudes of 30nm (12nm SL) and 15nm (6nm SL) and a wavelength of 400nm was determined. Threading dislocations were found with a density greater than 2×109cm−2. The superlattice interfaces are strongly bent in the region of the threading dislocations, undisturbed regions have a maximum lateral sie of 500nm. Thin films and SL showed a structural modulation [natural nanostructure (nns)] with a wavelength of 10nm and a wave vector parallel to (1,0,10). This nns was also observed in Bi2Te3 bulk materials and turned out to be of general character for Bi2Te3. The effect of the microstructure on the thermoelectric properties is discussed. The microstructure is governed by the superlattice, the nns, and the dislocations that are present in the films. Our results indicate that the microstructure directly affects the lattice thermal conductivity. Thermopower and electrical conductivity were found to be negatively correlated and no clear dependence of the two quantities on the microstructure could be found.

We report on an enhanced thermoelectric figure of merit ZT=sigmaS(2)T/lambda (where sigma is electrical conductivity, S is thermopower, T is absolute temperature, and lambda is thermal conductivity) for PbTe/PbSe0.20Te0.80 superlattices (SLs) and PbTe doping SLs due to a reduction of the thermal conductivity lambda parallel to the layer planes. Despite a small decrease of the power factors sigmaS(2) due to a reduction of sigma in these superlattices, the figure of merit is higher as compared to the corresponding bulk materials and reaches maximum values in the temperature range between 400 and 570 K

No abstract

Thermoelectric thin film micro-devices with high packing densities of thermoelectric legs are of high demand in micro-systems for self-standing and so called waste energy self-powered sensor systems for wireless data transfer. One technical solution for such micro-devices is offered by the Micropelt technology. The recent development status of the Micropelt micro thermogenerators will be presented. The Micropelt platform technology now allows devices with up to ~8000 p-n-couples per cm2. Open circuit voltages achieved so far were about 2.3 V at 10 K temperature difference. Maximum power output was measured to be 2.8 mW. Thus they are suited as power supplies for harvesting energy in stand alone sensor systems for wireless data transmission. An evaluation setup to perform first level tests for the efficiency of harvesting waste energy using the microstructured thermogenerators will be presented

No abstract

Up to now thermoelectric materials used in commercial energy conversion devices like infrared sensors, Peltier-coolers or thermogenerators do not take advantage of the enormous potentials provided by low-dimensional structures. The scope of this presentation is the experimental verification of the predicted increase of the thermoelectric figure of merit (FOM) ZT in low-dimensional systems above values of bulk materials. Concepts for the realization of devices using low dimensional structures based on the classical thermoelectric materials (V-VI-compounds for temperatures around 300 K and IV-VI-materials for temperatures up to 600 K, silicides for high temperature applications) were made. We will present briefly the preparation and thermoelectric properties of IV-VI and V-VI superlattice (SL) structures grown by molecular beam epitaxy as well as on Si-Ge SL structures grown by magnetron sputter epitaxy. An important part is the theoretical modeling of these new thin film devices. The results were used to determine the bests uited geometrical dimensions and to compare the calculated device performance with the experimental results. Further more, the results will be discussed with respect to the rising industrial interest in high performance thermoelectric thin and thick film devices

No abstract