Measurement of the diffusion length of minority carriers using a steady-state photocarrier grating

An improper orientation of the sample electrodes with respect to the interference fringes in the steady-state photocarrier grating (SSPG) setup can lead to large errors in the measured diffusion length (LL). A simple analysis shows that the measured LL is always larger than the actual LL if the sample is misaligned. The analysis compares well with the experimental data taken on a hydrogenated amorphous silicon sample.