Absorption and transport properties of Si rich oxide layers annealed at various temperatures

Abstract

Thin films of SiOx (x = 1.15, d = 1 and 2 µm), deposited by thermal vacuum evaporation of SiO on n- and p-type crystalline Si or quartz substrates, and then furnace annealed at 250, 700 and 1000 °C, are studied. Optical and infrared transmission measurements prove phase separation upon annealing at 700 and 1000 °C and growth of amorphous Si nanoparticles upon annealing at 700 °C, whose optical band gap is ∼2.6 eV. High-resolution electron microscopy data confirm growth of Si nanocrystals with average size ∼5 nm in the films annealed at 1000 °C. Both kinds of transmission data were used to estimate the nanoparticle volume fraction and values of 0.2–0.25 and 0.25–0.30 for the films annealed at 700 and 1000 °C, respectively, are determined. Current–voltage characteristics (at fields >5 × 104 V cm−1) are measured on metal/SiOx/c-Si/metal structures to explore carrier transport mechanisms in all kinds of samples. They are nearly symmetric, which indicates that in all samples carrier transport via structures is dominated by the transport in the SiOx layers. It is concluded that current transport is space-charge-limited for the layers annealed at 250 °C. In the films further annealed at 700 °C containing amorphous nanoparticles, Poole–Frenkel transport mechanism is reported while tunnelling is assumed for the films annealed at 1000 °C.