Nanoscopic Electric Potential Probing: Influence of Probe–sample Interface on Spatial Resolution

Electric potential probing on the nanometer scale elucidates the operation of actively driven conducting, semiconducting, insulating and semi-insulating devices and systems. Spatial resolution of this analysis technique is shown to depend on the time required for the voltage measurement circuit to reach steady state with the local electric potential of the sample. Scanning voltage microscopy on actively biased buried heterostructure lasers reveals this time to be intrinsically long (10−2 s to 1 s) and to depend on material doping type (n- or p-type) and scan direction (to increasing or decreasing sample potential). The bandstructure of the probe–sample interface is examined and is shown to provide high incremental contact resistance to an equivalent circuit model of the measurement circuit. Practical scan speed limits are defined for accurate scanning electric potential measurements given a desired spatial resolution.