Fabrication And Properties Of PVK/Ga₂O₃ Organic-inorganic Heterojunction Solar-blind Photodiode

Ultraviolet photodetector plays a key role in important fields,such as flame detection,imaging and missile warning systems,causing more and more research interests.As a representative of the third generation semiconductor materials,gallium oxide(Ga2O3)has a wide bandgap(4.2-5.3 eV),so it is an ideal alternative material for ultraviolet photodetection.In the research of ultraviolet photodetectors,inorganic-based devices have always occupied the largest market,but organic-inorganic heterojunction devices are gradually coming into our field of vision in recent years.Compared with inorganic-based devices,organic-inorganic hybrid devices not only have the advantages of low cost,easy production and light weight of organic material,but also often have better performace than inorganic-based devices.Among many orgainc materials,poly(n-vinylcarbazole)(PVK),as a hole transport material,has a wide bandgap(～3.6 eV),which is often used in photodetection and shows good performance.However,to the best of our knowledge,PVK/Ga2O3 organic-inorganic hybrid devices have not been reported.Herein,we fabricated a planar solar-blind photodiode based on PVK/Ga2O3 for the first time,and studied the influence of PVK layer thickness on the photoelectric performace of the device.The main research content of this thesis are as follows:(1)The planar structure of PVK/ε-Ga2O3 heterojunction photodiode was firstly fabricated on sapphire substrate by means of metal organic chemical vapor deposition(MOCVD)and spin-coating.The prepared ε-Ga2O3 thin film and PVK thin film were characterized by XRD and SEM,from which we found that the obtained thin films were continuous and compact,and the ε-Ga2O3 thin film has good crystallization properties.The photoelectric performance of the device was tested by the semiconductor test instrument.The results show that the device has an obvious rectifying characteristic of 37 under 254 nm UV light at±2 V.Under the voltage of 5 V,the rise time is 0.52s,and the decay time is 0.11s,suggested the response speed of the device is good.In addition,the I-t test of the device under the 0 V bias condition shows that the device has the potential of self-power operation.This new organic-inorganic heterojunction device is expected to be used in the future ultraviolet photodetection.(2)We also studied the influence of PVK thin film thickness on the photoelectric performance of the devices,and prepared PVK/β-Ga2O3 organic-inorganic photodiodes with three different thickness of PVK layers.By comparing and analyzing the I-t and I-V characteristic curves of each device,we speculated that with the thickening of PVK layer,the photoconductivity increased,so the current increased with the thickness,and the current also increased with the thickness at 0 V bias,but the rectification ratio decreased obviously with the thickness increases.In addition,we also found that the stability and repeatability of the devices are good though PVK thickness of the devices are changed.