In this work, the performance of a broadband laser light source in comparison to a halogen lamp for spatially resolved photocurrent spectroscopy studies in the wavelength range of 870-1250nm was evaluated. Measurements were performed using a monochromator and an atomic force microscope (AFM) with an electrically conducting tip on a self-assembled InAs/GaAs quantum dot test sample. The sample structure corresponds to a Schottky-i-n diode, the single dot layer was embedded within the intrinsic region of the sample.
The application of an AFM tip as a top electrode allows to determine the photocurrent with sub-micrometer (typically 50nm or better) spatial accuracy, which allows to selectively measure the photocurrent response of individual quantum dots and the single layer InAs quantum well. All spectra show a transition that can be attributed to interband excitation of the wetting layer. Signal intensities, spectral and spatial resolution, pressure and bias dependent behaviour were investigated. Results for the wetting layer were compared to photoluminescence measurements and good agreement between the photocurrent results and the photoluminescence spectra was found.