Study of the density of states of hydrogenated amorphous silicon from time-of-flight and modulated photocurrent experiments

Abstract

The densities of states (DOS) deduced from the modulated photocurrent (MPC) and the time of flight (TOF) techniques performed on two films of a-Si:H deposited in the same run are compared. For the MPC experiment the sample was built in the coplanar geometry whereas a Schottky diode was used for the TOF experiment. This comparison suggests that the MPC technique applied to a coplanar sample is sensitive to the electron trapping states. The influences on the MPC results of the flux and of the wavelength of the excitation light are studied. Probing the DOS closer to the illuminated interface by decreasing the wavelength, we observe a slight increase of the DOS, the increase on the a-Si:H/air side being more important than on the glass/a-Si:H side.