Thermal and field-induced generation mechanisms in polysilicon thin film transistors: A comparison between n-channel and p-channel devices

The presence of a high off-current in polycrystalline silicon thin film transistors is a major problem in view of the use of these devices in active matrix liquid crystal displays. Furthermore, due to the complex dependence of this current from both the temperature and applied bias, an accurate analysis of this phenomenon is required, in order to well understand the physical mechanisms involved. In this work we have measured the off current of both n- and p-channel devices over a wide range of temperatures, namely 140-400K. An analytical model which accounts for the temperature and electric field dependence of this off-current is proposed and the importance of both the gap density of states and the electric field distribution in the channel is discussed.