Characterization of the density of states of polymorphous silicon films produced at 13.56 and 27.12 MHz using CPM and SCLC techniques

Abstract

The aim of this paper is to compare the density of bulk states (DOS) of polymorphous silicon (pm-Si:H) films produced by plasma enhanced chemical vapor deposition at 13.56 and 27.12 MHz using the constant photocurrent method and the space charge limited current (SCLC) technique. The data achieved revealed that the set of films produced present similar DOS. Apart from that, data concerning the correlation of the deposition conditions that lead to the production of pm-Si:H as well as their characteristics, such as the hydrogen content and how hydrogen is bonded, will be discussed, giving special emphasis to the set of mechanical stresses developed. By doing so we could get a better understanding of the nature of hydrogen bonding in pm-Si:H films as well as to determine the role of the excitation frequency on the film's performances, where films with amounts of hydrogen around 20 at.% can have DOS as low as 8 × 10 14 cm −3 with Urbach energies in the range of 41–50 meV.