Research On MOS Structure Photodetector Based On Perovskite

Perovskite(CH₃NH₃PbI₃)is a new type of organic-inorganic hybrid photoelectric material,which not only has high carrier mobility,but also has the advantages of simple preparation and low price.Perovskite materials have a wide range of applications in various fields,especially in photovoltaics.Among them,the application of solar cells is the most well-known.The efficiency of solar cells prepared with them has increased from 3.8%in2009 to more than 25%at present.However,there is still much room for research in photodetectors.This article focuses on the study of metal/oxide/perovskite MOS photodetectors based on the leakage mechanism,and focuses on the process factors that affect the performance parameters of the detectors.First,a photodetector based on the metal-silica-perovskite MOS structure was prepared.Since the perovskite film is confirmed to have ion migration,due to its low binding energy and low activation energy(0.1-0.6 e V)and diffusion energy barrier(?0.17 e V),I^-is considered to be the main cause of ion migration..The migration and accumulation of a large number of ions will cause current hysteresis,which will affect the performance of the device.Therefore,it is believed that the concentration of I^-will affect the performance of the device.We add different concentrations of iodine to the perovskite precursor solution,and use Kysight B1500A to perform I-t,I-V,and C-V tests to compare the photoelectric characteristics of the corresponding devices.By comparing the photoelectric properties of the perovskite under light and dark conditions,the influence of mobile ions that are not shielded by photo-generated carriers and the changes in the photoelectric properties of the perovskite after light are observed.Studies have found that in the dark state,the increase of I^-concentration will increase the hysteresis of the perovskite MOS device.However,under illumination,due to the improvement of the quality of the iodine-doped perovskite film,a large number of photogenerated carriers not only shield the hysteresis phenomenon,but also show better photoelectric performance.The performance of the detector not only depends on the perovskite layer,but the optimization of other functional layers is also very important,especially the oxide layer.The optimization of its thickness also meets the requirements of gradual reduction in device volume.In this regard,the article uses a high dielectric to replace the traditional silicon dioxide method,so that the thickness of the oxide layer is reduced to 10%of the original.The research uses high-k dielectric(Al₂O₃ and Hf O2)as the oxide layer of MOS devices to study the optoelectronic properties of the devices.First,the atomic layer deposition process(ALD)was used to prepare Hf O2 and Al₂O₃,and the photoelectric characteristics before and after annealing were compared.The study found that as the density of Al₂O₃ increases after annealing,defects are reduced,and the number of ions latched in the Al₂O₃ and Hf O2 defects is reduced,so that the I-V hysteresis becomes smaller.Correspondingly,when it is not annealed,there are more defects,and the greater the thickness of alumina,the more mobile ions in the perovskite that can be introduced,resulting in greater hysteresis.The Al₂O₃ prepared by the ALD method has fewer defects and good compactness,which provides a direction for the reduction of the photoelectric hysteresis,but also weakens the photocurrent.For this reason,we use the relatively loose film magnetron sputtering method(PVD)to prepare Al₂O₃.At the same time,in order to be able to more comprehensively study the impact of each functional layer in the MOS device on the performance of the photodetector,the article starts from the polishing method of the silicon wafer substrate,the thickness of the oxide layer,and the thickness of the perovskite film.These three aspects have been experimentally explored:1)When a double-polished silicon wafer is used as a substrate,its photocurrent value is larger than that when a single-polished silicon wafer is used as a substrate,and the photoelectric hysteresis is smaller.2)When the thickness of Al₂O₃ is 30-50 nm,the photocurrent of the corresponding photodetector is large,and the photodetection rate and responsivity reach the maximum.When the thickness of Al₂O₃ increases to 70 nm,the blocking effect of the oxide layer on carriers increases,which reduces the photocurrent.When the Al₂O₃ is reduced to 10 nm,although the barrier effect of the oxide layer on the carriers is reduced,the roughness of the alumina is higher at this time,which affects the growth of the perovskite,resulting in fewer photogenerated carriers.3)When the perovskite film is 200 nm,the light absorption rate is low,and the corresponding photocurrent is also low.When the thickness of the perovskite film is increased to 300 nm,light absorption and carrier transport have achieved a good balance,and the device performance reaches the best.Continue to increase the thickness of the perovskite film to 400 nm,although it can generate more photogenerated carriers,but because the diffusion length of the carriers cannot cover the thickness of the entire film,some electron-hole pairs recombine,which makes the photocurrent value compared to the perovskite film at 300 nm The growth is weak.From the above conclusions,it can be known that the metal/alumina/perovskite-based MOS photodetector can achieve high resolution when the double-polished silicon wafer is used as the substrate,the thickness of alumina is 30 nm,and the thickness of perovskite is300 nm.It can not only achieve high-performance detection effects,but also reduce the volume in a large extent.