Hydrogen microstructure in hydrogenated amorphous silicon

We present a method to determine the local hydrogen bonding structure in hydrogenated amorphous silicon from infrared spectroscopy measurements. This approach is based on a different oscillator strength and refractive index for hydrogen atoms located in the isolated and clustered phase. It is demonstrated that the density of distributed hydrogen atoms does not exceed 3-4 at.%, independent of the deposition conditions for several deposition techniques. We suggest that changes in the infrared-absorption strength upon ion bombardment or light soaking can be attributed to a hydrogen exchange between clustered and isolated phases.