Numerical simulation of transient emission from deep level traps in polysilicon thin film transistors

Abstract

Numerical simulation was used to model transient carrier emission from deep level traps in polycrystalline silicon (poly-Si) thin film transistors and to validate the analytical approximations used to interpret DLTS measurements. Transient emission from a single trap was compared with that from a continuous density of states. Numerical simulation was used to quantify the degree of error in the analytical analysis and show that it yields substantially correct values for a typical double exponential poly-Si trap state density as a function of energy, to within ± 10%. The major source of discrepancy was associated with the omission of the effects of displacement current from the analytical analysis. The DLTS spectra associated with a constant density of states was shown to give a decreasing signal with decreasing temperature, while that of an exponential density of states was found to be essentially flat.