LATERAL RESOLUTION OF LIGHT-ADDRESSABLE POTENTIOMETRIC SENSORS - AN EXPERIMENTAL AND THEORETICAL INVESTIGATION

The surface potential of semiconductor devices in contact with electro lyte solutions is an important part of signal transduction for a varie ty of bioanalytical devices. Here we have investigated the lateral res olution at which the surface potential may be measured with a semicond uctor-based device, a light-addressable potentiometric sensor (LAPS). We have first established an experimental setup where a permanent char ge pattern is generated in the oxide-nitride interface of an n-doped s ilicon wafer by UV irradiation. Using a laser beam to interrogate the LAPS, the charge pattern can be detected by measuring the local photoc urrent ata resolution of better than 100 mu m. A theoretical model bas ed on the diffusion and recombination of photogenerated minority charg e carriers has been developed and solved analytically; it is consisten t with experiment. For Beer-Lambert law absorption of a sufficiently n arrow beam of interrogating light, according to the theory the lateral resolution depends on the relative sizes of the penetration depth of the light, d, and the recombination-diffusion length of the carriers, L. When d much less than L,the resolution is (2Ld)(1/2); when L much g reater than d, it is (2L(2))(1/2). (C) 1997 Elsevier Science S.A.