On the sensitivity of transient photodecay measurements as a probe of localised state distributions in amorphous semiconductors

An investigation is reported of the extent to which structure in the density of localised states in amorphous semiconductor films may be detected from photodecay measurements. Transient photocurrents are computed by a Monte Carlo technique, for the case of an exponential tail of states upon which a sharp rectangular feature has been superimposed. It is shown that a ‘rectangular’ component of energy width kT must protrude from the background exponential tail by at least a factor of 5 in density, in order to exert a readily-detectable influence upon the transient photodecay. It is further demonstrated that the presence of deep-lying features in the distribution of localised states may easily modify the transient decay over a wide range of time; underlining the difficulty of interpreting such data.