Inner electric field mechanism of tunneling of electron-hole pair in porous silicon

Abstract

Recently a porous silicon model of radiative recombination of electron-hole pair through luminescence center outside the nanoscale Si unit was proposed by Qin et al. In order to test it we calculated the transmission coefficient (TC) of electron-hole pair in terms of a coupled double quantum box model and an inner electric field mechanism. According to this mechanism an inner electric field will be established as soon as some electrons tunnel through the SiO 2 barrier. This field will reduce the TC of electron, T e and increase the TC of hole, T h . As long as T e > T h , this field will increase monotonically until it reaches an equilibrium inner electric filed, E eq at which the TCs of electron and hole approach the same value, T pair which is just the TC of electron-hole pair in steady state. In this paper, we calculated T pair and E eq as functions of the thickness of SiO 2 barrier for coupled double quantum boxes, lines and layers. The results show that the TC of electron-hole pairs is increased by taking into account the equilibrium inner field. This fact supports the proposal of pair recombining outside the silicon unit, since a sufficiently early TC of pairs is the precondition for efficient recombination. Our results are of importance for further calculations of the quantum efficiency of photoluminescence in porous silicon.