Unpinning of the Fermi level on GaAs (100) surfaces by photochemical reactions resulting from simultaneous exposure of specimens to flowing water and light was recently reported. We discuss here a series of experiments carried out to provide further information on the changes in surface electronic structure responsible for unpinning of the Fermi level under these conditions. The present work supports the conclusion that the surface states which pin the Fermi level are associated with elemental arsenic and arsenic sesquioxide (As2O3). Effects of each of these two species on pinning are distinguished experimentally. We find that, in addition to photochemical reactions, exposure to flowing water alone can result in Fermi level unpinning under certain conditions. The oxygen content of the wash water and the specimen preparation are shown to be important variables.
Extensive investigations by a number of groups have identified catastrophic sudden degradation as the main failure mode in both single-mode and multi-mode InGaAs-AlGaAs strained quantum well (QW) lasers. Significant progress made in performance characteristics of broad-area InGaAs strained QW single emitters in recent years has led to an optical output power of over 20W and a power conversion efficiency of over 70% under CW operation. However, unlike 980nm single-mode lasers that have shown high reliability operation under a high optical power density of ~50MW/cm 2 , broad-area lasers have not achieved the same level of reliability even under a much lower optical power density of ~5MW/cm 2 . This paper investigates possible mechanisms that prevent broad-area lasers from achieving high reliability operation by performing accelerated lifetests of these devices and in-depth failure mode analyses of degraded devices with various destructive and non-destructive techniques including EBIC, FIB, and HR-TEM techniques. The diode lasers that we have investigated are commercial MOCVD-grown broad-area strained InGaAs single QW lasers at ~975nm. Both passivated and unpassivated broad-area lasers were studied that yielded catastrophic failures at the front facet and also in the bulk. To investigate the role that generation and propagation of defects plays in degradation processes via recombination enhanced defect reaction (REDR), EBIC was employed to study dark line defects in degraded lasers, failed under different stress conditions, and the correlation between DLDs and stress levels is reported. FIB was then employed to prepare TEM samples from the DLD areas for cross-sectional HR-TEM analysis.
Bullets were characterized by lead isotope ratio analysis and trace element analysis in two homicides. In one case, we concluded that a fatal bullet did not share a common origin with bullets in a box of ammunition containing 24 cartridges taken from suspects. Evidence in the second case included two bullets from the crime scene and 163 bullets taken from various suspects. We were able to infer that the two bullets from the crime scene did not share a common origin and that they differed from all of the bullets taken from suspects. All of the suspects' ammunition had been reloaded as was evident both from trace and isotopic analysis and, indeed, from visual inspection.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.