Deep trapping controlled switching characteristics in amorphous silicon thinhyphen;film transistors

摘要

We report transient effects in amorphous silicon thinhyphen;film transistors occurring upon switchhyphen;on and switchhyphen;off, which are controlled by trapping and emission from the deep states in the amorphous silicon. We develop a unifying theoretical description which is applicable to both switchhyphen;on and switchhyphen;off. The model is based on carrier thermalization to the deep states and includes the spatial dependence of the thermalization process in the bandhyphen;bending region. The model is able to explain the experimentally observed switchhyphen;on and switchhyphen;off behavior. In the case of switchhyphen;on, electrons are progressively trapped into the deep states in the bulkahyphen;Si:H throughout the entire thickness of the layer. The range of trapping times is large and this leads to a dynamic threshold votage shift and a time dependence of the sourcehyphen;drain current extending between 1 mgr;s and 1 s. In the case of switchhyphen;off, two processes occur sequentially. First, there is emission of electrons from the bulkahyphen;Si:H deep states, which leads to a uniform space charge throughout the thickness of the layer. After that, a redistribution of the space charge occurs, leading to the eventual thermal equilibrium spacehyphen;charge distribution. These processes give rise to two different time constants in the measured decay of the total charge stored in the transistor. Full thermal equilibrium can take several hours to reach.