Fermi level dependence of the ambipolar diffusion length in amorphous silicon thin film transistors

The steady-state photocarrier grating technique was applied to measure the ambipolar diffusion length (Lamb) in a-Si:H thin film transistors. With this device we studied the Fermi level dependence of Lamb through the variation of the gate voltage. The experimental results show that Lamb decreases whereas the photoconductivity increases with positive gate voltage. We simulated the Fermi level dependence of electron and hole mobility-lifetime products and found good agreement with the measured diffusion length.