The external performance of quantum optoelectronic devices such as multi-quantum-well lasers is governed by their inner workings—as described by the spatial profiles of electrons, holes and potentials. Without an experimental means of probing these inner distributions, the chief mechanisms responsible for sub par device performance remain speculative at best.

This work reveals through new experiments the connection between physics and function—between nanoscopic origins and macroscopic utility. New methods in scanning probe microscopy are established and deployed to probe inside lasing multi-quantum-well devices. Scanning voltage microscopy is validated and calibrated and scanning differential spreading resistance microscopy is developed. These two techniques are then applied to delineate quantitatively potentials and carrier densities inside devices under forward bias.

This work yields direct observation of internal behavior of operating buried heterostructure (BH) and ridge waveguide (RWG) multi-quantum-well lasers. It addresses four important issues regarding mechanisms limiting laser performance. The first direct observation of current blocking failure in a BH laser under high current injection is reported. Diode current leakage, as opposed to thyristor current leakage, is identified as the leading cause of blocking structure failure. The first direct and quantitative observation of current spreading inside actively-biased RWG lasers is reported. The local current density at the edge is ∼40% smaller than that at the center of a 2.4 μm ridge width under a current of 150 mA. The nanoscopic origins of anomalously high series resistance in some RWG lasers are witnessed directly for the first time. The work reports the first direct experimental observation of electron overbarrier leakage in operating BH MQW lasers at room temperature.

This work demonstrates and exploits the first experimental visualization of the inner workings of operating semiconductor lasers. The techniques developed and demonstrated open a new field in applied nanoscience:​ probing nanoscopic devices in vivo.