Hole Transport in MOS Oxides

Abstract

Hole and electron transport are reported for three different kinds of MOS oxides: wet, dry, and ion-implanted. The electron-hole pairs are generated in the bulk of the oxide by a 3 ns x-ray pulse and the separation of the electron and hole photocurrents is made possible by the large difference in mobility. The electrons are so mobile that they are swept from the oxide (or trapped in a heavily ion-implanted region) during the x-ray pulse. The holes, on the other hand, have much lower mobilities which depend strongly on the preparation of the oxide. In the dry oxide the nominal mobility at room temperature is several orders of magnitude higher than in the wet oxide. The mobility is strongly activated by temperature in the oxides, and at liquid N$sub 2$ temperature no hole motion could be detected even though the electrons are still swept out. The low temperature charging of oxides can be understood in terms of the bulk trapped holes, but room temperature charging seems to be dominated by trapping close to the Si/SiO$sub 2$ interface rather than the transport of the holes from the bulk to the interface. Ion implantation provides electron traps which seem to be associatedmore » with the lattice damage rather than the ion. The electron traps can be successfully annealed out at 900$sup 0$C in 20 minutes. (auth)« less