OPTICAL NEAR-FIELD INDUCED CURRENT MICROSCOPY

A scanning near-field optical microscope operating in the visible in i llumination mode and using 80 nm tapered aluminum-coated optical fiber tips is used in order to investigate spatially resolved photogalvanic effects in semiconductors. The measured signal, referred to as Optica l Near-Field Induced photocurrent (ONIC), is mapped as a function of t he tip position on the sample surface. In this mode of operation, the sample is also the photodetector. ONIC microscopy is tested on artific ially fabricated subwavelength-sized nanostructures with known photoco nducting properties. Using ONIC microscopy, we have accurately and dir ectly measured the diffusion lengths of minority carriers photogenerat ed in heavily n-doped GaAs crystals.