Study On Vertical Photoresponsive Organic Field-effect Transistors

With the high-speed development of informationization,large scale integrated circuits technology and terminal display technology become the most important support techniques in information-based society.Traditional semiconductor techniques have disadvantages such as complicated preparation engineering,not suit for flexible substrate and large area production,and high investing cost.Organic semiconductors have been extensively used in Photoelectronics because of its advantages of lightness,low-cost and compatible to flexible substrate.Based on photoinduced effect, photoresponsive organic field-effect transistors(PhotOFETs) can amplify photo-generated current by its transconductance.With their wide applications,PhotOFETs have recently been demonstrated as a kind of promising devices in fabricating full organic displays and organic photodetectors,and it has become an important leading topic in organic transistor.In this paper,by focusing on improving the structure of PhotOFETs,we fabricated the vertical photoresponsive organic field-effect transistors(Vertical PhotOFETs) in which the channel length can be reduced to nanometers,and it doesn't need to use Lithography. The performance of our devices was characterized and factors affecting their characteristics were analyzed in detail.Firstly,MEH-PPV-based Vertical PhotOFETs were fabricated and characterized, and the impact of different insulating layers on device performance was investigated. The "ON/OFF" current ratio(I_on/I_off) of 8 and the current ratio under light to that in dark(I_Ph/I_Dark) of 50 and light sensitivity is 46 mA/W was obtained with SiO₂ as insulating layer when the I_DS=-5 V and I_GS=4 V.The thickness of MEH-PPV layer of 90 nm as the photosensitive layer in vertical PhotOFETs shows a relatively good performance.Secondly,Pentacene-based vertical PhotOFETs were fabricated,and the impact of different dielectric layers on device performance was investigated.The I_on/I_off of 70,the I_Ph/I_Dark of 12 and the light sensitivity of 12 mA/W were obtained with SiO₂ as insulating layer when the I_DS=10V and I_GS=-4 V.The I_on/I_off of 6,the I_Ph/I_Dark ratio of 40 and the light sensitivity of 8mA/W were obtained with LiF as insulating layer when the I_DS= 10 V and I_GS=-4 V.The thickness of Pentacene layer of 80 nm as the photosensitive layer in vertical PhotOFETs shows a relatively good performance.Finally,we use the open environment of high temperature oxidation to the oxidation of silicon for 180nm silicon oxide as gate dielectric layer and to produce a complete device.The I_on/I_off of 6,the I_Ph/I_Dark of 10 and the light sensitivity of 13 A/W were obtained with MEH-PPV as Photosensitive layer when the I_DS=-5 V and I_GS=2 V. The I_on/I_off of 120,the I_Ph/I_Dark of 30 and the light sensitivity of 22 A/W were obtained with MEH-PPV as photosensitive layer when the I_DS=-2 V and I_GS=5 V.Because of the drain leakage current and the charge carriers tunneling Schottky barrier due to the mass collective charges at the interfaces,Si-based devices get a big operating current,and the phenomena of zero-point shifting occurs.