Yan Guoying

Effect of microstructure on the thermoelectric properties of CSD-grown Bi2Sr2Co2Oy thin films

Three Bi2Sr2Co2Oy thin films with different microstructures have been prepared by chemical solution deposition on LaAlO3(001) through varying the annealing temperature. With the decrease in the annealing temperature, both the size and c-axis alignment degree of grains in the film decrease as well, leading to an increase in the film resistivity. In addition, the decrease in the annealing temperature also results in a slight increase in the Seebeck coefficient due to the enhanced energy filtering effect of the small-grain film. The nanostructured Bi2Sr2Co2Oy film with an average grain size of about 100 nm shows a power factor comparable to that of films with larger grains. Since the thermal conductivity of the nanostructured films can be depressed due to the enhanced phonon scattering by grain boundary, a higher figure of merit is expected in Bi2Sr2Co2Oy thin film with grains in nanometer size.

High temperature thermoelectric properties of highly c-axis oriented Bi2Sr2Co2Oy thin films fabricated by pulsed laser deposition

High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co2Oy thin films prepared by pulsed laser deposition on LaAlO3 (001). Both the electric resistivity ρ and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K–1000 K and reach up to 4.8 mΩ cm and 202 μV/K at 980 K, resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples. A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature. The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application in high temperature thin film thermoelectric devices.

The Enhancement of Laser-Induced Transverse Voltage in Tilted Bi2Sr2Co2Oy Thin Films with a Graphite Light Absorption Layer

Laser-induced transverse voltage effect is investigated in c-axis tilted Bi2Sr2Co2Oy thin films coated with a graphite layer by using three different laser sources with wavelength ranging from ultraviolet to near-infrared. Due to the transverse thermoelectric effect, voltage signals are detected when the film surface is irradiated by these three lasers and the voltage sensitivity is enhanced as a result of the increasing light absorption at the graphite layer. This work demonstrates that the graphite can be used as an effective absorption layer for fabrication of light detectors based on the photo-thermo-electric conversion.

Temperature-dependent rectifying and photovoltaic characteristics of an oxygen-deficient Bi2Sr2Co2Oy/Si heterojunction

A Bi2Sr2Co2Oy/Si heterojunction is obtained by growing a layer of p-type oxygen-deficient Bi2Sr2Co2Oy film on a commercial n-type silicon wafer by pulsed laser deposition. Its rectifying and photovoltaic properties are studied in a wide temperature range from 20 K to 300 K. The transport mechanism under the forward bias can be attributed to a trap-filled space-charge-limited current conduction mechanism. Under the irradiation of a 532-nm continuous wave laser, a clear photovoltaic effect is observed and the magnitude of photovoltage increases as the temperature decreases. The results demonstrate the potential application of a Bi2Sr2Co2Oy-based heterojunction in the photoelectronic devices.