Pyrochlore Oxides Thin Films For Photodetectors

Pyrochlore oxides belong to an important class of electronic functional materials.The chemical formula of pyrochlore oxides is A₂B₂O₇.As long as the conditions of ion radius and electrical neutrality are met,the A and B can be replaced by other chemical elements extensively.As a result,the macroscopic properties of the material can be greatly changed,showing a great application value.Y₂Hf₂O₇ is a wide-bandgap semiconductor with an optical bandgap width of approximately 5.0 eV,which corresponds to the absorption of 250 nm solar-blind ultraviolet photons.Replacing all Hf with Ir,Y₂Ir₂O₇ is a semiconductor with narrow optical band gap about 0.4 eV,which corresponds to the absorption of 3?m mid-wave infrared photons.The quaternary compound Y₂(Hf_x,Ir_1-x)₂O₇ is composed of Y₂Hf₂O₇ and Y₂Ir₂O₇.In theory,by changing the Hf/Ir atomic percentage of the material,the Y₂(Hf_x,Ir_1-x)₂O₇ band gap can be changed between 5.0⁰.4 eV,which meets the needs of photoelectric detection in the ultraviolet to mid-wave infrared.So,Y₂(Hf_x,Ir_1-x)₂O₇ can be used in photodetectors as a photoelectric detection material with great value.Therefore,this paper carried out preliminary research on the photoelectric detection performance of Y₂(Hf_x,Ir_1-x)₂O₇ thin film.The main research results obtained are as follows:Y₂Hf₂O₇ thin films were grown on?100?oriented yttrium stabilized zirconia?YSZ?single crystal by magnetron sputtering.X-ray diffraction?XRD?and scanning electron microscope?SEM?,High-resolution transmission electron microscope?HRTEM?and other means were used to characterize the Y₂Hf₂O₇ thin films.The research results shown that the high-quality Y₂Hf₂O₇ epitaxial film was successfully prepared under optimized conditions,which was good for its physical properties and device development.After the fabrication of Y₂Hf₂O₇ thin film,in order to accurately characterize the optical characteristics of Y₂Hf₂O₇ thin film,amorphous quartz glass was used as a substrate to grow Y₂Hf₂O₇ thin film.According to the transmission spectrum measurement results,the optical band gap of Y₂Hf₂O₇ thin film was calculated as a result of about 5.1 eV.As the rule of thin film epitaxial growth,the Y₂Hf₂O₇ film grown on the surface of amorphous quartz glass should have a polycrystalline structure.However,XRD analysis results shown that the Y₂Hf₂O₇ film grown on the surface of amorphous quartz glass shows highly consistent texture characteristics.The Y₂Hf₂O₇?111?crystal plane was parallel to the substrate surface,showing a different rule from the common film epitaxial growth,which may be related to the crystal structure characteristics of pyrochlore oxide.This experimental discovery not only provided experimental datas for the preparation of Y₂Hf₂O₇ thin films using Si/SiO₂ substrates,but also provided the possibility of monolithic integration of the detector and the readout circuit.For this reason,the paper finally chosed Si/SiO₂ as the substrate to grow Y₂Hf₂O₇ thin film.After further optimization of the process parameters,a high-quality Y₂Hf₂O₇ thin film was prepared on the surface of the Si/SiO₂ substrate under the growth conditions of the substrate temperature of 600?and the total sputtering pressure of 0.5 Pa,providing material support for the development of photodetector devices.This paper used microfabrication technology to fabricate the device electrodes on the high-quality Y₂Hf₂O₇ thin film.Electrode beam evaporation technology was used to deposit electrodes,and a photodetector with MSM?metal-semiconductor-metal?structure was developed on Y₂Hf₂O₇ thin film.Excellent photoelectric responses were observed in dark condition and under the 245 nm ultraviolet light,such as photo-current to dark-current ratio of 119,photo-responsivity of 139 A/W,and detectivity of 3.8×10¹³ Jones.The device has fast response speed with rise time?25 ms?and the decay time?50 ms?,indicating that Y₂Hf₂O₇ film is a good candidate for solar blind UV detection.Based on the research on the solar-blind ultraviolet characteristics of Y₂Hf₂O₇ thin film,Ir was partially used to replace Hf to expand the spectrum coverage of the detectors,and the characteristics of Y₂(Hf_x,Ir_1-x)₂O₇ thin film were studied.The preliminary research results shown that partial substitution of Ir for Hf had a greater impact on the band gap and conductivity of Y₂(Hf_x,Ir_1-x)₂O₇ thin film,indicating that Y₂(Hf_x,Ir_1-x)₂O₇thin film may be an important candidate material for photoelectric detection.