A model describing the electrical behavior of a-SiN:H alloys

The electrical properties of plasma-deposited amorphous silicon nitride hydrogen alloys (a-SiN:H) deposited at different rf powers were determined. The N–H and Si–H content of these films were determined using a Fourier transform infrared spectrometer. The N–H content was relatively insensitive to the deposition conditions; however, the Si–H content was very sensitive to the deposition conditions. The conductivity of the films was found to depend upon the Si–H content [Si–H] and was given by σ=7.25×10−21 exp(2.74×10−21[Si–H]) at 70 °C and 4×106 V/cm. The high-temperature activation energy (i.e., trap height) was also strongly dependent on the Si–H content. A model is proposed which qualitatively explains the electrical behavior of the films. The material is considered to be a two-phase mixture: Phase 1 is highly structured (Si3N4-like) which has a low level of defects, and a low hydrogen content; Phase 2 is highly disordered with a high concentration of Si–H and N–H defect states and a high hydrogen content. At low temperatures the disordered structure controls the conductivity and at high temperatures the ordered phase controls the conductivity. The percentage of phase 2 decreases with decreasing hydrogen content. This decrease causes an increase in the trap height that leads to an exponential decrease in the mobility which in turn causes the conductivity to decrease exponentially.