Scanning-laser-microscope measurements of minority-carrier diffusion length and surface recombination velocity in polycrystalline silicon
A scanning laser microscope was used to study the electronic and recombination properties at grain boundaries of both n- and p-type Wacker polycrystalline silicon in a spatially resolved photoconductivity experiment. The light energy falling on the samples was varied over five orders of magnitude from 10−1 to 10−6 mW. For p-type material the measured L decreased with beam intensity from 150 to 60 μm, reaching a constant value at very low beam intensities. The small focal spot of the microscope allowed the measurements to be extended to include n-type samples. Forthese samples L was found to change from 90 to 18 μm with decreasing beam intensity. The surface recombination velocity SGB was evaluated for both samples. For p-type samples it decreased from 25 000 to 6000 cm/s and for n-type samples from 21 000 to 3000 cm/s with decreasing beam intensity. The quasi-Fermi level separation was determined as a function of the excess minority-carrier-concentration density at the grain boundary and found to increase linearly with beam intensity.
Comment on ‘‘Evaluation of the minority carrier diffusion length and edge surface‐recombination velocity in GaAs p/n solar cells’’ [J. Appl. Phys. 72, 2919 (1992)]