Study On Dual-gate Photo-responsive Organic Field-effect Transistors

Photo-responsive organic field-effect transistor?PhotOFET?has attracted more and more attention in recent years and becomes a hot field in the research of organic photodetectors.Moreover,compared with organic photodiodes,photo-responsive field effect transistors have higher sensitivity and lower noise current.And the devices based on organic material have the characteristics of simple preparation process,low cost,flexibility,printability,stretchability and so on.It has very important applications in imaging,optical sensing,optical detection and other fields.Compared with the conventional single-gate photo-responsive organic field-effect transistor,the dual-gate photo-responsive organic field-effect transistor has the advantages of high gain and wide spectrum response.Based on a large amount of literature research and organic electronics theory,one type of PhotOFET is prepared and studied in this thesis.These devices can work in both independent and collaborative modes.The experimental results show that the mobility and photoresponsivity of double gate device are improved compared with single gate.When the same type complementary dual photosensitive layer is used,the device can show wide spectral response characteristics.When using a special complementary dual photosensitive layer,the device can display dual optical wave detection characteristics.The specific work content and innovation points of this thesis can be summarized into the following three parts:First,based on PhotOFET structure,the mobility characteristics are studied under the illumination.CuPc,pentacene and C60 are used as active layer materials.Gold?Au?,silver?Ag?,aluminum?Al?and copper?Cu?are used as electrodes.Its channel length varies from 25¹00?m.The results show that carrier mobility under illumination is always greater than mobility under dark for different source-drain materials and channel lengths.With the increase of illumination power,the carrier mobility increases linearly at first,reaching a certain value and approaching saturation.For certain electrode materials,the saturated lighting mobility increases with the decrease of channel length.For a certain channel length,its saturation lighting mobility of PhotOFET based on CuPc with silver electrode is the highest,but the saturation lighting mobility of PhotOFET based on pentacene with gold electrode is the highest.Secend,a dual-gate PhotOFET is prepared with CuPc as photosensitive layer,n⁺⁺-Si/SiO2 as bottom gate and bottom gate dielectric,PVA or PVP as top gate dielectric and ultra-thin Au film with transmittance over 70%as top gate electrode.Its photoelectric characteristics are studied.The gradual change concentration spin-coating process is developed,which can effectively improve the quality of PVA film.By inserting a LiF?thickness⁵ nm?protective layer between the photosensitive layer and the top gate dielectric layer,the dark current of the device is effectively reduced.The results show that the mobility of the dual-gate PhotOFET is at least 60%higher than that of the single-gate PhotOFET.For 650nm laser response,the specific detectivity D*of the device reaches 2.3?10¹³ cm?Hz^1/2/W?Jones?.Photoresponsivity R is 414 A/W.Third,a dual-gate PhotOFET with two-photosensitive layers based on CuPc and SnPc is prepared.Its photoelectric characteristics are studied.The operating principle of this PhotOFET is interpreted systematically.The device achieves a wide spectral response from 500 nm to 900 nm.A dual-gate PhotOFET is prepared with PTCDA and CuPc as hetero two-photosensitive layers.The device realizes dual-band optical detection with the central wavelength at 532 nm and 650 nm.For 532 nm laser illumination,the maximum photoresponsivity R_max of the device is 503 mA/W.For650 nm laser illumination,the maximum photoresponsivity R_max of the device is 4.52A/W.