Thermally stimulated detrapping in porous silicon

A thermally stimulated current (TSC) methodology has been used to reveal the mechanisms of detrapping in porous Si (C. Bucci, R. Fieschi, G. Guidi, Phys. Rev. 148 (1966) 816). This thermally stimulated method consists of electrically polarizing a sample at temperature, T0, which is depolarized consequently during heating, giving rise to a depolarization or trap-discharge displacement current which can be recorded. When double layer dielectric-semiconductor materials such as porous silicon on a heavily doped silicon substrate are subjected to an electret formation cycle, charge trapping may easily occur. This is explained by the fact that the heterogeneity at the interface between Si and PSi is the source of numerous discontinuities and imperfections in the Si crystal in addition to those existing in the porous layer, all of which are capable of capturing electric carriers because the transition region near the interface may also produce new allowed electron states in the bandgap. The electrical behaviour of the whole material is affected by such an internal structure which is mostly similar to an extended semiconductor surface due to its pores (R.C. Anderson, R.S. Muller, C.W. Tobias, J. Electrochem. Soc. 138 (1991) 3406). Thus, one may state that the electrical properties of PSi are close to those of a surface dominated semiconductor. In the present work an attempt has been made to calculate the activation energy of hole traps within porous Si.