INTERNAL AND EXTERNAL CHARACTERISTICS IN TRANSIENT FORWARD BIAS SIMULATIONS OF A-SI-H DEVICES

A numerical program for transient modeling of multilayer a-Si:H devices is described. Using a computer simulation, transient currents in a-Si:H PIN and NIN devices using different magnitudes of step voltage excitations were studied. The results of calculations show first a rapid drop in electric current, followed by an intermediate interval of current rise in both devices. During longer limes after step excitation, the transient current in a NIN device decays monotonically towards the new steady-state value, while the current in a PIN device shows a sudden rise to its final value. Such behaviour is explained on the basis of calculated results for different internal quantities such as free and trapped carrier concentrations, space charge density, electric field, potential, net recombination rates and others. It is shown that initially the current in both devices is space-charge limited. The presence of both types of carrier in a PIN diode enables space-charge neutralization at the end of the transient, causing the final abrupt current increase and transition to recombination-limited current flow. The influence of varying the density of localized states (DOS) on simulated transient currents is analyzed and discussed.