Lateral resolution of light-addressable potentiometric sensors: an experimental and theoretical investigation

Abstract The surface potential of semiconductor devices in contact with electrolyte solutions is an important part of signal transduction for a variety of bioanalytical devices. Here we have investigated the lateral resolution at which the surface potential may be measured with a semiconductor-based device, a light-addressable potentiometric sensor (LAPS). We have first established an experimental setup where a permanent charge pattern is generated in the oxide-nitride interface of an n-doped silicon wafer by UV irradiation. Using a laser beam to interrogate the LAPS, the charge pattern can be detected by measuring the local photocurrent at a resolution of better than 100 μm. A theoretical model based on the diffusion and recombination of photogenerated minority charge carriers has been developed and solved analytically; it is consistent with experiment. For Beer-Lambert law absorption of a sufficiently narrow 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 ⪡ L, the resolution is (2Ld) 1 2 ; when L ⪢ d, it is (2L 2 ) 1 2 .