NEAR-FIELD OPTICAL BEAM-INDUCED CURRENT MEASUREMENTS ON HETEROSTRUCTURES

We report near-field optical beam induced current (NOBIC) measurements on semiconductor quantum well (QW) structures. A subwavelength fiber tip is coupled with a tunable laser source and scanned over a sample s urface. The induced photocurrent reveals the compositional profile of quantum structures. Semiconductor QW structures were designed and fabr icated by molecular beam epitaxy (MBE) to study the wavelength depende nce and resolution capability of NOBIC. We demonstrated that the resol ution of this technique strongly depends on the aperture size. For ape rture sizes that allow for coupling of evanescent fields from the tip into the semiconductor as propagating fields, the resolution strongly depends on the excitation wavelength due to the variation of the optic al penetration depth. For smaller apertures, the optical field remains evanescent in the semiconductor and resolution is essentially indepen dent of the wavelength. (C) 1995 American Institute of Physics.