A novel contrast mechanism of emission mode near-field microscopy applied to diode laser structures

Summary form only given. Near-field scanning optical microscopy (NSOM) is currently evolving into an important analytical tool for optoelectronic devices. Here, a powerful approach is to use the fiber tip of the NSOM as an excitation light source when the investigated device itself serves as a detector. This can be considered as an extension of the optical/laser beam induced current/voltage (O/LBIC/V) technique beyond the diffraction limit. Consequently this kind of emission-mode NSOM is termed near-field optical beam induced current/voltage NOBIC/V. Since NOBIC/V signals are rather weak, lock-in amplification is generally used to obtain sufficient signal-to-noise ratios. In most experiments, only the amplitude of the NOBIC signal is analyzed whereas the phase information is usually ignored. We report here new experiments, which use the phase of NOBIV signals as a novel contrast mechanism that allows, for example, QWs to be located within the waveguide. The results that are obtained by using high-energy excitation (2.8 eV) are compared with data for resonant waveguide excitation (780-820 nm), which allow for a quantitative analysis of the waveguide properties of both laser structures.