ON THE ROLE OF HYDROGEN IN METASTABLE DEFECT EQUILIBRATION IN UNDOPEDHYDROGENATED AMORPHOUS-SILICON

An equilibration (''freeze-in'') temperature, T-eq, was measured in un doped hydrogenated amorphous silicon, a-Si:H, as a function of hydroge n content. A constant T-eq is approximately equal to 220 degrees C was observed for bonded hydrogen content in the range 0.29 to 12.6 at .%. Subgap optical absorption and photoconductivity measurements were use d for the determination of the T-eq. Because of the sufficiently wide range of hydrogen content in the samples investigated, several importa nt consequencies concerning the microscopic models of metastability in a-Si:H can be drawn. Our data do not support the present version of t he widespread ''Hydrogen Glass Model'' for undoped a-Si:H.