Structure and electrical conductivity of nanocomposite SiOxNy(Si) and SiAlzOxNy(Si) films

Abstract

In this study, the peculiarities of the structure and electrical conductivity of nanocomposite SiOxNy(Si) and SiAlzOxNy(Si) films in the temperature range of 95 – 340 K are determined. The composite films were obtained by ion-plasma sputtering of Si and co-sputtering of Si and Al targets in oxygen and nitrogen containing atmosphere (Ar+O2 +N2) followed by high temperature annealing. During the annealing of the deposited Si rich oxynitride films, Si nanoinclusions were formed in an amorphous dielectric matrix due to phase separation. Al atoms are found to be in the bound state (no Al metal nanoparticles present). The films have low absorbance and considerable transparency in the ultraviolet – visible – near infrared spectral region. Reduction of some part of Si-O bonds by Al during annealing the Al-containing samples leads to the separation of higher Si concentration as compared to the Al-free samples. The electrical conductivity of the films at low electric fields is found to be by variable-range electron hopping through the traps near the Fermi level. The characteristics of the traps and transport process such as the density of electron traps near the Fermi level, the activation energy of hopping and the hopping length are determined. It is found that the electrical conductivity of the SiAlzOxNy(Si) films annealed in argon is higher as compared to the films annealed in nitrogen and the Al-free films due to higher concentration of electron traps. The region of the conductivity decrease with the increase of electric field is revealed on the current-voltage characteristics of both the SiAlzOxNy(Si) films annealed both in nitrogen and argon and the SiOxNy(Si) films annealed in nitrogen. This effect is explained based on the peculiarities of electric field polarization in the films. The important role is played by the interface traps at the Si nanoparticle / amorphous matrix interfaces that capture electrons. At high electric fields, the film conductivity corresponds to the space charge limited current mechanism with the exponential distribution of the traps in the energy gap.