Fabrication And Modeling Of Ambipolar Hydrogenated Amorphous Silicon Thin Film Transistors PDF Download

The hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) has been studied extensively for several years. Its application as a switching element in large area liquid crystal display arrays has been demonstrated. Modeling studies have been performed to quantify and explain the performance of the a-Si:H TFT. However, throughout these investigations little has been reported concerning the ambipolar nature of the a-Si:H TFT; that is, the ability of the device to operate alternatively as an n-channel or a p-channel device. The work described in this thesis extends the previous by specifically addressing the ambipolar behavior of the a-Si:H TFT. In particular, a process sequence has been developed to fabricate high quality ambipolar a-Si:H TFTs with emphasis on ohmic source/drain contacts. Using experimental data from these devices and TFT theory, a model has been developed for obtaining the output drain current vs. drain voltage of ambipolar a-Si:H TFTs. The model involves the numerical integration of an interpolated sheet conductance function. By using the appropriate flat-band voltage, the model accurately predicts the experimental output drain current characteristics for both n- and p-type operation over many orders of magnitude.