PHOTOCARRIER GRATING TECHNIQUE IN MESOPOROUS SILICON

We present the first measurement of the ambipolar diffusion length in mesoporous silicon using the steady state photocarrier grating technique. Taking also response time measurements into account, we can deduce a typical value of the ambipolar diffusion coefficient of about 1.8 x 10(-6) cm(2) s(-1). The mobility-lifetime products of majority and minority carriers are found to be (mu tau)(mai) = 10(-8) cm(2) V-1 and (mu tau)(min) = 7 x 10(-10) cm(2) V-1 respectively. Together with temperature-dependent dark conductivity and intensity-dependent secondary photocurrent measurements we argue that a high density of trap states with a broad energetic distribution is responsible for such a small diffusion coefficient.