Correlation of Surface Topography and Coating Damage with Changes in the Responsivity of Silicon PIN Photodiodes
SourceLaser-induced morphological damage initiated by single 10 ns, 1.06 μm Nd:YAG laser pulses was observed on three types of EG&G silicon PIN photodiodes. When the samples were irradiated at fluences above the melting threshold, the damage morphologies were observed to vary according to the type of coating and the fluence. Nomarski microscopy at 200X was used to analyze the laser-induced topography at the damage sites. The topography was characterized generally by ripples, ridges and boiling marks in order of increasing fluence. However, all test fluence levels remained below the threshold for electrical degradation and no increase in leakage current was detected. The detector responsivity at the damage sites was mapped by means of a probe laser. The sample was translated within its plane in order to obtain a series of raster scans across each damage site. A comparison of the topographical data and responsivity data suggests that local variations in responsivity were correlated with laser-induced surface roughness and with the removal of the thin-films.