SURFACE-RECOMBINATION AND DOPING EFFECTS ON THE MINORITY-CARRIERS IN POLYCRYSTALLINE SILICON

A scanning laser microscope was used in a spatially resolved photoconductivity experiment to determine the minority-carrier diffusion length (L) and surface-recombination velocity at grain boundaries (S//G//B) in (i) n- and p-type Wacker polysilicon and (ii) neutron-transmutation-doped Metron polysilicon as a function of beam intensity. Different values of L were measured on opposite sides of the grain boundaries. For the Metron samples, L was measured at the same grain boundary using a series of samples doped to different levels. These samples had dopant concentrations between 10**1**3 and 10**1**7 atoms/cm**3. L was found to decrease from 50 to 5 mu m, with decreasing beam intensity, reaching a constant value at low beam intensities. L was also found to remain relatively unchanged for low dopant concentrations. The S//G//B values were found to increase with increasing beam intensity in both Wacker and Metron samples, ranging between 10**4 and 10**5 cm/s. L was also measured with a light-beam-induced-current technique (perpendicular geometry) and found to be in close agreement with values obtained using the photoconductivity technique.