Fabrication And Thermoelectric Properties Of Oriented SnSe Thin Films

Tin selenide(SnSe)is a novel thermoelectric material with excellent performances,which shows great application potential in various fields including thermoelectrics.So far,most studies on the thermoelectric properties of SnSe have been carried out on bulk materials and there are very few reports on thin films.However,SnSe single crystal bulks usually show poor mechanical properties and easy to crack,which make them unsuitable for fabricating devices;After polycrystallization,the orientation of SnSe single crystal bulks deteriorated and the thermoelectric properties degraded dramatically.Compared with three-dimensional bulk materials,two-dimensional thin film materials are easier to realize orientational growth,which is beneficial for thermoelectric property improvements due to their anisotropic characteristics.In addition,the fabrication process of two-dimensional thin film materials is compatible with modern semiconductor technology,showing irreplaceable advantages in thermoelectric microdevices integration.In this paper,a-axis oriented SnSe thin films were prepared by pulsed laser deposition(PLD)and their thermoelectric properties were studied in detail.The main research contents and conclusions are as follows.1.SnSe thin films were prepared on different single crystal substrates(MgO,STO,LAO,LSAT)by PLD technology.The crystal structure,surface morphology,element composition,microstructure and transport properties of SnSe thin films were studied in detail by XRD,SEM,XPS,TEM and thermoelectric measurements.The results revealed that SnSe thin films grown on four substrates were all single crystal films along a-axis orientation,among which the films grown on MgO substrates by epitaxy exhibited the best crystallization quality.At 573 K,this sample showed excellent thermoelectric properties with a ZT value as high as 1.38.2.SnSe thin films with a-axis orientation were grown on polyimide(PI)flexible substrates by PLD technology.Electrical performance measurements showed that the thermoelectric power factor of SnSe flexible thin films at about 600 K was 3.5 ?W/cm?K,which is lower than epitaxial SnSe film on MgO substrate,but its still higher than single crystal bulks.After repeated bending,the orientation of the flexible film deteriorated,which led to a sharp decrease in power factor,and the stability of the flexible film need to be further improved.3.SnSe oriented films with a-axis tilted growth were prepared on tilted single crystal substrates by PLD technology,and the transverse thermoelectric effect of the films was studied for the first time.It was found that when the surface of the thin film was irradiated by heat source or laser with different wavelengths,a large open-circuit voltage output signal can be observed on both sides of the surface,and the amplitude of the signal can be effectively modulated by the irradiation power of the laser or heat source,the tilt angle of the thin film and the temperature gradience on the film.These results show that SnSe thin films have potential applications not only in thermoelectric devices,but also in wide-band photodetectors and thermal sensors.