Preparation And Performance Study Of Photodetectors Based On Ga₂O₃/BiFeO₃ Thin Film Heterojunction

Gallium oxide（Ga₂O₃）is a wide band gap semiconductor,it has an ultra-wideband gap of about 4.8-5.1 eV and a Baliga’s figure of merit more than 3000+,which makes it stand out in the research field of ultraviolet（UV）photodetectors.Ga₂O₃ has five phases that can be transformed into each other under different conditions,among which β-Ga₂O₃ has received the most attention and application because of its best stability.with βUltraviolet photodetectors based on Ga₂O₃ are widely used in fire safety detection,optical fiber communication,missile guidance and medical imaging.The common structures of UV photodetectors based on(3-Ga₂O₃ include metal semiconductor metal structure（MSM）,Schottky diode structure,field effect transistor structure and heterojunction structure.Regardless of the detector structure,the contact between metal and film and the contact between film interface play an important role in the performance of the device.Both heterojunction and Schottky junction can produce potential barriers at the interface contact,which can effectively restrict or promote the transport of carriers.In this paper,we choose to use bismuth ferrite（BiFeO₃,with a band gap of about 2.7 eV,which often shows significant photovoltaic effect in existing detectors）films and Ga₂O₃ films to construct heterojunctions.Based on Ga₂O₃/BiFeO₃ heterojunction,we prepared Ga₂O₃/BiFeO₃ heterojunction UV photodetector.The main research results include:1.Firstly,through the understanding of the film preparation method,the film preparation method suitable for the material itself is selected.High quality sapphire films were successfully prepared on sapphire substrates by metal organic chemical vapor deposition（MOCVD）β-Ga₂O₃ film,in βBiFeO₃ thin films were successfully prepared on Ga₂O₃ thin films by magnetron sputtering and solution spin coating,respectively.The X-ray diffraction patterns（XRD）,scanning electron microscopy（SEM）and UVvis absorption spectra of the two films and heterojunctions were analyzed.These results prove that the growth process of the film is rigorous and the grown film is of high quality.At the same time,it is proved that the design and preparation of heterojunction are successful.2.Based on high-quality Ga₂O₃/BiFeO₃ heterojunction,Ti/Au point electrode was fabricated on the surface of the film by magnetron sputtering,and the photodetector was prepared.The photoelectric properties of the device,such as current voltage and current time,were tested by Keithley 4200 semiconductor analyzer and UV lamp.The spectral responses of different wavelengths were measured by a monochromator with xenon lamp spectrometer.Several important quality factors for the detector are calculated,analyzed and compared comprehensively.3.Ga₂O₃/BiFeO₃ heterojunction UV photodetector was prepared by MOCVD+magnetron sputtering.In this work,a broadband UV-Vis photodetector with a dark current(I_dark) of 0.12 pA was prepared and characterized based on Ga₂O₃/BiFeO₃ heterojunction.At light intensity of 100 μW cm^-2 under UV light 254 nm,the bias voltage is 2 V,a high light dark current ratio（PDCR）is 1.0×10⁵,a response（R）is 12.0 mA·W^-1,a detectivity（D^*）is 6.1 ×10¹² Jones,an external quantum efficiency（EQE）of 5.9%and an UVC/visible light suppression ratio(R₂₃₅/R₆₀₀)of 4.47×10³.In addition,the device shows excellent performance in the UV lamp on-off cycle test,and can keep stable in the cycle for a long time.The rise time and decay time are 0.25 s and 0.04 s respectively.At the same time,the photocurrent of 10^-10 A under 0 V bias proves the potential of the device as a self-powered photodetector.The results show that Ga₂O₃/BiFeO₃ heterojunction is a potential candidate material for broadband detection.4.Ga₂O₃BiFeO₃ heterojunction UV photodetector was prepared by MOCVD+Solution spin-coating method.Under the condition of completely unbiased driving,the device achieves 1.66×10³ light dark current ratio（PDCR）,high detectivity（D^*）of 6.1×10¹² Jones and high open circuit voltage(V_OC)of 0.55 V under 254 nm UV light.In addition,the device has a good response to very weak light intensity,indicating its sensitive light detection ability.The results show that Ga₂O₃/BiFeO₃ heterojunction is a potential candidate material for self-powered deep UV photoelectric detection.5.For the construction of Ga₂O₃/BiFeO₃ heterojunction,we designed two different schemes according to different preparation methods of BiFeO₃ thin films.According to the results,both schemes are successful.The basic photoelectric performance of photodetectors based on different preparation methods is similar,and they are prominent in wide-band detection and self-powered operation.In addition,it is compared with similar heterojunction photodetectors with simple fabrication method and simple structure.The results show that Ga₂O₃/BiFeO₃ heterojunction photodetectors have certain advantages in performance.Therefore,the research of ultraviolet photodetector based on Ga₂O₃/BiFeO₃ heterojunction is reliable and comprehensive.