Optical absorption in amorphous hydrogenated silicon nitride thin films deposited by the electron cyclotron resonance plasma method and subjected to rapid thermal annealing

Abstract

We have analyzed the influence of rapid thermal annealing (from 300 to 1050 degrees C) on the optical properties of a-SiN(x):H. Three compositions were investigated: x = 0.97, x = 1.43 and x = 1.55. Two different behaviors are observed depending on whether the as-grown nitrogen to silicon ratio of the samples is above or below the percolation threshold (x = 1.1) of Si-Si bonds, in the matrix of silicon nitride. The samples with x: = 1.43 and 1.55 experience an increase of the Tauc coefficient (B) and a decrease of the Urbach parameter (E(0)) at low annealing temperatures. while at high temperatures the trend is inverted. On the contrary, the samples with x = 0.97 show a slight and continuous increase of B and a similar decrease of E(0). The different behavior of the films with x < 1.1 is explained by the percolation of the Si-Si bonds, which maintains the order of the structure at high annealing temperatures, preventing the inversion of the trends of B and E(0).