For the modeling of infrared spectra it is a common approach to use a dielectric function that treats the vibrational modes as damped harmonic oscillators. This model was found to be rather crude for some applications to amorphous solids. A dielectric function model yielding a Gaussian shape of the absorption lines and satisfying Kramers–Kronig relations is suggested. The model function is constructed by a convolution of a Gaussian function with the dielectric function of the damped harmonic oscillator model. An analytical solution of this integral is given. It is demonstrated that this model describes the spectra of thermally grown ultrathin (1.3 nm) silicon oxide films, plasma‐deposited silicon films, plasma‐deposited silicon nitride films, and amorphous aluminum oxide films very well. The physical motivation of the dielectric function model suggested is the randomness of the vibrational frequencies in an amorphous structure.

An infrared dielectric function model for amorphous solids

Silicon Nitride is found to have a valence band maximum of nitrogen lone pair p electrons because of the planar nitrogen site. This contrasts with the usual lone pair semiconductors, such as SiO2, caused by a p4 valence configuration. Consequently although the valence band density of electron states shows a lone pair band and a deeper bonding band as usual, impurities have a greater effect in the nitride than in conventional lone pair semiconductors. Hole transport is also discussed.

Electronic structure of silicon nitride

We have analyzed the role of the bond densities of a-SiNx:H films on the passivation properties at the SiNx:H/Si interface. The films are deposited onto silicon wafers by plasma enhanced chemical vapor deposition using a 13.56 MHz direct plasma system and a SiH4/N2/H2 gas mixture. Fourier transform infrared spectroscopy measurements are performed in order to obtain the bonding concentration of Si–Si, Si–H, Si–N and N–H. The passivation properties are deduced by lifetime measurements using a microwave-detected photoconductance decay technique. Carrier lifetimes of the SiNx:H-passivated silicon wafers of up to 1200 μs correlate to surface recombination velocities, Seff, as low as 4–6 cm/s. This means that the films provide excellent passivation of silicon surfaces, which is necessary for high-efficiency solar cells. The Si–H bond density and the total bond density are considered as measures of the passivation quality. Models for the formation of K+ centers and for the passivation pathways during the plasma ...

Detailed study of the composition of hydrogenated SiNx layers for high-quality silicon surface passivation

A comparative micro-cantilever study of the mechanical behavior of silicon based passivation films

The effect of deposition conditions on characteristic mechanical properties – elastic modulus and hardness – of low-temperature PECVD silicon nitrides is investigated using nanoindentation. It is found that increase in substrate temperature, increase in plasma power and decrease in chamber gas pressure all result in increases in elastic modulus and hardness. Strong correlations between the mechanical properties and film density are demonstrated. The silicon nitride density in turn is shown to be related to the chemical composition of the films, particularly the silicon/nitrogen ratio.

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Effect of deposition conditions on mechanical properties of low-temperature PECVD silicon nitride films

The composition of hydrogenated silicon nitride films produced either by plasma-enhanced chemical-vapor deposition (PECVD) with 0.01\ensuremath{\le}[${\mathrm{NH}}_{3}$]/[${\mathrm{SiH}}_{4}$]\ensuremath{\le}20 in the 220--320-\ifmmode^\circ\else\textdegree\fi{}C temperature range or by low-pressure chemical-vapor deposition at 800 \ifmmode^\circ\else\textdegree\fi{}C was determined by elastic-recoil-detection techniques and compared with the relative and absolute atomic densities deduced from x-ray photoelectron spectroscopy and optical measurements in the infrared (ir) range. The [N]/[Si] ratio of PECVD samples followed a square-root dependence on [${\mathrm{NH}}_{3}$]/[${\mathrm{SiH}}_{4}$] over most of the gas-ratio range. We propose original calibrations of most of the ir-absorption bands observed in these samples over the 600--3600-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ range, and we derived the experimental bond statistics by assuming complete valence satisfaction. In particular, the oscillator-strength factor of each of the six components of the SiH stretching peak was determined. The detailed statistics of all the hydrogenated configurations established for the first time in such a silicon-based ternary alloy are then compared to those expected to those expected for a random-bonded network. The most striking deviations from configurational randomness were observed at low nitrogen contents where more than two out of three silicon neighbors of a given nitrogen atom are monohydrogenated. Nitrogen atoms are found to have at least one monohydrogenated silicon nearest neighbor in all samples up to [N]/[Si]=1.1. The generality of such a second-neighbor correlation in hydrogenated III-IV amorphous alloys is also discussed.

S. C. Gujrathi

Papers

Configurational statistics in a - Si x N y H z alloys: A quantitative bonding analysis