Abstract
The high‐temperature hydrogen evolution process from undoped hydrogenated amorphous silicon (a‐Si:H) is known to be diffusion limited. A formula is derived by which the hydrogen diffusion coefficient can be inferred from hydrogen effusion spectra taken at different heating rates or on films of different thickness. Experimental results for glow‐discharge a‐Si:H films prepared at various laboratories are presented and an excellent agreement to literature data of the hydrogen diffusion coefficient is obtained for undoped and phosphorus‐doped samples. For boron‐doped films, on the other hand, surface desorption of hydrogen from internal surfaces (voids) is found to be the rate‐limiting process for hydrogen evolution.