Effect of light-soaking on the hydrogen effusion mechanisms in polymorphous silicon thin film structures

• We study hydrogen effusion due to light-soaking in pm-Si:H PIN and NIP structures.
• Hydrogen diffuses from the bottom layer to the top layer and effuses.
• Hydrogen diffusion process depends on the device structure (PIN or NIP).
• A hydrogen diffusion barrier is generated by defects while trying to effuse on PIN.
• Light-soaking increases the effused hydrogen and is more pronounced on the NIP.

This work describes a study performed on hydrogenated polymorphous silicon PIN and NIP structures, deposited by plasma enhanced chemical vapor deposition (PECVD). We study hydrogen stability and its evolution during exodiffusion experiments in these structures, trying to determine the effect of light-soaking pre-treatments on the hydrogen effusion mechanisms. We examined the structural and optical properties of PIN and NIP structures after exodiffusion experiments. These were analyzed in terms of the different hydrogen diffusion processes comparing light-soaked samples and samples without light-soaking. Also, an analysis of both structures was done in order to determine which one is less affected by light-soaking. From the simultaneous measurement of temperature and hydrogen desorption, we propose a model for long range diffusion of hydrogen. We show that long range motion of hydrogen during light-soaking and annealing causes a hydrogen rearrangement on the film and microstructure changes which result in a shift on the exodiffusion peaks. Both structures were compared and are discussed in terms of the hydrogen bonding configurations and environment. We determined that for the PIN structure a hydrogen diffusion barrier is generated by light-induced defects, which is expected to cause less degradation of its optoelectronic properties under illumination, and a more stable device during operation along with an enhanced functional performance of this type of structure.