Direct observation of electron overbarrier leakage in actively driven buried heterostructure multi-quantum-well lasers

Abstract

We have developed a new scanning probe microscopy - based technique, scanning differential spreading resistance microscopy (SDSRM) and applied it to profile the free carrier distribution inside operating optoelectronic devices. The results of our SDSRM study of multi-quantum-well (MQW) buried heterostructure (BH) lasers under zero and forward biases are presented. SDSRM scans with high spatial resolution over the MQW active region of a BH laser yielded quantum-well-resolving differential spreading resistance measurements. The SDSRM results show the changes of internal carrier distribution within the MQW active region in BH lasers upon the application of forward biases. In combination with scanning voltage microscopy results, the SDSRM measurements provide direct experimental evidence of electron overbarrier leakage due to heterobarrier lowering, which has been speculated in theoretical modelings. Our results demonstrate the strength of SDSRM in probing the inner workings of operating quantum optoelectronic devices on nanometer scale, in which conventional analytical techniques such as secondary ion mass spectroscopy (SIMS), scanning spreading resistance microscopy (SSRM), and electron beam induced current microscopy can either apply only to devices under zero bias or provide only qualitative pictures.