Control of photodegradation in amorphous silicon: The effect of deuterium

Light-induced changes in the photoconductivity and defect density have been compared in deuterated and hydrogenated amorphous silicon. There is no significant difference between the as-deposited properties of the two materials; however, the photoconductivity degrades more slowly but anneals more rapidly in material prepared using the heavier isotope. In hydrogenated material, the average photocarrier recombination cross-section of the defects increases with light soaking but the opposite occurs in deuterated material. These results are explained in terms of two kinds of recombination centre which are photocreated at different rates. The variation in the degradation and annealing behaviour of photoconductivity with deposition temperature implies subtle structural differences between the two materials which, for the first time, gives rise to the possibility of controlling photodegradation in amorphous silicon.