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

Abstract

Thin films of SiO x (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 × 10 4 V cm −1 ) are measured on metal/SiO x /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 SiO x 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.

Structural, compositional and electrical characterization of Si-rich SiOx layers suitable for application in light sensors

“…In the first group of samples (c-Si/SiNPs-SiO x ) the dielectric was formed by deposition of an $ 80 nm thick SiO x (x¼1.15) layer which was further furnace annealed in a nitrogen (N 2 ) atmosphere at 700 or 1000 1C for 60 min to grow amorphous or crystalline Si NPs, respectively. The SiO x layers in all groups of samples were prepared by thermal evaporation of silicon monoxide in vacuum [9,10]. In the second and third group of structures a SiO 2 layer with thickness of $ 25 nm was thermally grown at 1000 1C for 5 min in dry oxygen.…”

“…Since the total annealing time for all the samples was 60 min one can expect approximately equal Si nanoparticle size in all structures annealed at the same temperature. Our previous results have proven that 60 min annealing of SiO 1.15 in N 2 at 700 1C causes phase separation and formation of amorphous silicon nanoparticles in a SiO x matrix with x¼ 1.8-1.9 [9,16], while annealing at 1000 1C leads to growth of 5-6 nm Si nanocrystals in a SiO 2 matrix [9,17]. Control samples were also produced by annealing at 250 1C for 30 min in an argon atmosphere.…”

“…A standard method to obtain Si nanoclusters is high temperature furnace annealing of sub-stoichiometric SiO x layers. The SiO x films are usually deposited by Chemical Vapor Deposition (CVD) [1], plasma-enhanced CVD (PECVD) [7] or Physical Vapor Deposition (PVD) [8,9] techniques. The high temperature annealing promotes silicon aggregation and at temperatures of about 700 1C amorphous Si nanoparticles are formed [10], while at T4900 1C Si nanocrystals (Si NCs) are grown [11].…”

Application of Metal-Oxide-Semiconductor structures containing silicon nanocrystals in radiation dosimetry

“…The top 6−7 nm of the SiOx film are depleted of NCs and atomic force microscopy measurements revealed that the films annealed at 1000 ∘ C have a smooth surface. The Si volume fraction (filling factor f ) determined is f = 0.2 and 0.28 for the films with x = 1.3 and 1.15, respectively [28]. More details on the film preparation and previously obtained Si-SiO 2 characteristics can be found in Ref.…”

“…Normally Si nanocrystals are grown by an additional annealing at 1000 ∘ C in N 2 atmosphere for 60 min. The growth of isolated randomly distributed Si NCs in a SiO 2 matrix (Si-SiO 2 composite) has been proven by X-ray Photoelectron Spectroscopy (XPS) [27], infrared transmission [28,29] and Transmission Electron Microscopy (TEM) investigations. The TEM results have shown an average NC size of 3−5 nm in the x = 1.3 films and 4−6 nm in the x = 1.15 ones [29,30].…”