Characterisation of defects in hydrogenated amorphous silicon thin film

Abstract

We report detailed characterization of thermal equilibration, metastability and light induced metastability in n-type hydrogenated amorphous silicon a-Si:H resistive devices. After the anneal, the samples were cooled at a rate of 0.5 K/s. Temperature dependencies of the low-frequency noise were studied from room temperature to about 420 K. The Arrhenius plots of voltage noise power spectra exhibit two different regimes separated by a kink at about 380K in their temperature dependencies. It is noted that the kink can be eliminated provided the subsequent cooling rate after the 450K annealing process is lowered to about 0.02 K/s. The characterization of the temperature dependencies of the device conductance exhibit the same equilibration temperatures as the flicker noise. Our experimental data provides strong evidence that the flicker noise originates from hydrogen motion within the material. In the second part of our experiments, the devices were exposed to 500W Xe lamp and HeCd laser. After the illumination, the Fouier Transform Infrared Spectroscopy (FTIR), Positron Annihilation Spectroscopy (PAS), and time dependencies of the low-frequency noise were studied. The experimental data showed that, the defect density of the sample decreased after illumination. It is suggested that the illumination, process led to light induced annealing effect.