Variation of the optical (Tauc) gap, Eg as a function of NH3 to SiH4 flow ratio (R), in the plasma.
Variations in the room temperature dark conductivity (σD), photo conductivity (σph), and the corresponding photosensitivity (S) as a function of increasing optical (Tauc) gap, Eg for the nc-Si/a-SiNx:H films prepared at increasing R.
Arrhenius plot of the dark conductivity (σD) of the nc-Si/a-SiNx:H films prepared at different R. Inset demonstrates the high temperature section of the same, demonstrating the thermally activated conduction above room temperature.
Variation of the high temperature activation energy (Ea) with optical (Tauc) gap, Eg. Inset demonstrates the pre-exponential factor (σ0) of dark conductivity as function of activation energy Ea. The solid line is a linear regression fit to the data.
The reduced activation energy, , plotted against T on a log-log scale for R = 0.3, identifying three different temperature regimes with individual slopes, in a sawtooth-like profile and recognizing three different conduction phenomena to be in effect.
(a) Plot of σd vs T in log-log scale, demonstrating a power-law temperature dependence of conductivity ( ) due to MPH below room temperature, with systematically enhanced y for increasing R; and (b) variation of ln(σd) with T−1/4 identifying Mott-VRH to be in effect, for samples with 0.3 ≤ R ≤ 0.5, below certain temperature that increases with R.
Variation of room temperature mobility (μe) and carrier concentration (ne), estimated from Hall-effect measurement, with increasing optical (Tauc) gap, Eg.
3D representation of the typical XRD pattern for the nc-Si/a-SiNx:H film having wide optical gap, Eg = 2.59 eV, corresponding to R = 0.3. Inset demonstrates the variation of I(220)/I(111) with Eg.
3D representation of the typical first order Raman spectrum, deconvoluted into three satellite components, for the nc-Si/a-SiNx:H film having Eg = 2.59 eV, corresponding to R = 0.3. Inset demonstrates the variation of total crystalline volume fraction (XC) and its ultra nanocrystalline component (Xunc) with increasing Eg.
TEM micrographs with low and high magnifications for the nc-Si/a-SiNx:H films prepared at R = 0, 0.2, 0.3, and 0.4. Corresponding histograms demonstrate the distribution of number density with size of the Si nanocrystals, in each case. The graph at the bottom demonstrates the variations of average size of the Si nanocrystals with corresponding number density and sharpness of distribution (FWHM) as a function of optical band gap, Eg.
Comparison on the nature of variation of the optical (Tauc) gap with nanocrystallite size estimated from various spectroscopic and microscopic studies (XRD, Raman spectra, and HR-TEM).
2D and 3D AFM images of the films prepared at R = 0 and R = 0.3.
FE-SEM image demonstrating the columnar growth morphology of the nc-Si/a-SiNx:H network prepared at R = 0.3.
Nature of variation of the room temperature dark conductivity (σD) of the nc-Si/a-SiNx:H films with changes in overall crystallinity (XC). Inset demonstrates the improvement of photosensitivity (S) with the dominance of ultra nanocrystalline component (Xunc) present in the network.
Variations of (a) the optimum hopping distance, rh, and (b) the hopping activation energy, Wh, with temperature, demonstrating both having higher magnitude for higher Eg, however, admitting different nature of temperature dependence.
A comparative analysis, correlating room temperature dark conductivity and optical band gap, among various works reported on the development of silicon and silicon related dielectric films deposited by different CVD processes.
Mott-VRH data for the nc-Si/a-SiNx:H films prepared at different NH3 to SiH4 flow ratio, R.
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