New results on the modulated photocarrier grating technique

A modulated photocarrier grating technique (MPG) has been used to measure s ome properties of amorphous silicon samples. The intermediate region where neither the lifetime, tau, nor the dielectric relaxation time, tau(d), are dominant and local charge neutrality may not be maintained has been investi gated. Light intensity dependence of the small-signal Lifetime estimated fr om a modulated photocurrent technique (MPC) was also studied. A qualitative agreement has been found between the data and the MPG theory which shows t hat this technique measures the response time/relaxation time ratio. Based on the results we suggest an overestimate of the ambipolar diffusion length obtained by the steady-state photocarrier grating technique (SSPG) in thes e samples which is an indication that local charge neutrality is not preser ved. (C) 2000 Elsevier Science B.V. All rights reserved.