Influence of deposition pressure on the bulk and interface states in low pressure chemical vapor deposited polycrystalline silicon thin‐film transistors

The effect of deposition pressure, p, on the bulk and interface states of undoped low pressure chemical vapor deposited polycrystalline silicon thin‐film transistors (polysilicon TFTs) is investigated by field‐effect conductance activation energy measurements. The bulk states consist of deep states with a characteristic wide peak near the midgap and shallow exponential tails near the conduction band. The interface states show an exponential distribution which cause a faster change of the gap states density near the conduction‐band edge. For p≳40 mTorr, the bulk and interface states are controlled by the grain size and the degree of disorder of the material. For p<40 mTorr, the experimental results indicate that the films are contaminated by some impurities. The concentration of these impurities increases as p decreases and contributes mainly to the deep states generation.