Complex Dielectric Characteristics, ac-Conductivity, and Impedance Spectroscopy of B-Doped nc-SiO_X:H Thin Films

Temperature-dependent ac conductivity, impedance spectroscopy, and complex dielectric properties have been investigated on boron-doped silicon oxide (SiOX:H) films grown by radio frequency plasma-enhanced chemical vapor deposition at low temperature (∼250 °C). The two-phase characteristics, e.g., silicon nanocrystals (Si-ncs) embedded in amorphous oxide (a-SiOX:H) tissues, have been evaluated initially by structural studies and subsequently via impedance spectroscopy. Impedance spectroscopy also facilitates identifying the contribution of each individual phase (nanocrystalline and amorphous) on the electronic properties of the materials. The dependence of relaxation time on temperature obeys Arrhenius behavior and also confirms a non-Debye type response under the varying electric field. The negative temperature coefficient of resistance behavior reveals the semiconducting nature of the materials. A designed equivalent circuit model using parallel R∥CPE shows comprehensive correlation among structural, microstructural, and charge carrier characteristics. Frequency-dependent conductivity follows Jonscher’s power law non-linear fitting and reveals a less than unity magnitude of its exponent “n”. The temperature dependence of ac conductance identifies a non-overlapping small polaron tunneling mechanism prevailing in the B-doped SiOX:H network. The tunneling distance is higher in B-doped nc-SiOX:H, and it reduces faster at higher frequency in the B-doped a-SiOX:H matrix. The charge carrier density of states, N(EF), is higher in nc-SiOX:H; however, the lower N(EF) of B-doped a-SiOX:H enhances faster at elevated frequency. The frequency-dependent electrical transport in the B-doped nanocrystalline/amorphous heterostructured SiOX:H network has never been explored before.