Geometric components of charge pumping current in SOS devices

Charge-pumping measurements of the spectral distribution of interface states are performed on three SOS device structures. In contrast to bulk devices with similar channel geometries, there is significant bulk recombination in addition to the normally present interface-state recombination. The bulk recombination produces a sharp upturn in the interface-state density near the bandgap edges. This upturn is an artifact of the analysis method. While it has been observed at both edges of the bandgap, it is usually stronger near the conduction band for n-channel devices and near the valence band for p-channel devices. In the remainder of the bandgap, the interface-state density is accurately measured. Following X-ray exposure, the interface-state density increases, whereas the upturns near the band edges are virtually unchanged. Unlike the case for bulk devices, it is shown that geometric constraints on the motion of majority carriers play an important role in producing recombination at bulk traps. A model is presented that addresses the carrier motion and describes the dependence of the bulk recombination on the channel geometry