On the existence of submicron diameter current shunts in morphologically perfect device layers

Abstract

On the existence of submicron diameter current shunts in morphologically perfect device layers Wasilewski, Z. R.; Dupont, E.; Weyher, J. L.; Laframboise, S.; Buchanan, M.; Liu, H. C.Contact us / Contactez nous: nparc.cisti@nrc-cnrc.gc.ca. (2002) 182]. The hot-spots, with surface densities varying from 20 to 3000 cm À 2 for the wafers studied, are LED electroluminescence singularities, which can be readily observed at temperatures below $ 100 K. Their spatial FWHM is less than 1 mm and they can have peak intensities of more than three orders of magnitude higher than the uniform background emission caused by the dark current through the QWIP device. In most cases the hot-spots were observed on mirror smooth, morphological defect-free surfaces. These electroluminescence abnormalities result from highly localized electron injection channels in the QWIP portion of the device. As there is no morphological abnormality in their locations, these defects are undetectable with established wafer screening instruments such as Nomarski and Surfscan, yet may be very common in MBE-grown heterostructures. Although correlation with dislocations is observed, the great majority of dislocations do not give rise to the hot-spots, and there are many hot-spots, which are not located in the proximity of any dislocation. We therefore, propose that the hot-spots arise from a local alloy separation in ternary layers, induced by floating organic molecules or molecular contamination clusters, resulting in nanowire-like defects. Highly localized drops in the layer resistivity caused by such defects will adversely affect the performance of any devices relying on vertical transport, particularly if the device current depends very strongly on the height of the potential barriers employed, such as in quantum well infrared photodetectors or resonant tunneling diodes. Also, for devices working at high current densities, such as certain lasers or HBTs, the presence of such defects may lead to early device failure. Crown

Broadband THz to NIR up-converter for photon-type THz imaging

“…4b to reveal the signal strength. The dark or bright spots on the picture is known as the LED emission hot spot at low temperatures with low injection level 37 . The present image is not a perfect circle because the actual effective area of the device is 700 × 700 μm 2 by deducting the top ring electrode, which is only a little larger than the diameter of the blackbody source hole (635 μm).…”

“…The net photocurrent and emitted power increase suddenly at about 1.7 V. The luminescence between 1.4 V to 1.7 V (at low temperature and low driving current) is caused by the hot spot in the device. The hot spot is caused by the material defects or surface imperfections 37 . Meanwhile, normal LED luminescence (not caused by hot spot) happens between 1.74–2.5 V, which agrees with Fig.…”

Cryogenic characteristics of GaAs-based near-infrared light emitting diodes

“…Wasilewski et al have systematically investigated the hot spots with reliable experiment [29]. The formation mechanism of the hot spots was explained as the low resistance path caused by a local alloy separation in ternary layers, induced by floating organic molecules or molecular contamination clusters caused nanowire-like defects [29]. This could also explain the origin of the hot spots in the single DH-LED and QW-LED studied in this work.…”

“…The localized bright EL spots called hot spots have been observed in the integrated (QWP-LED) up-conversion devices. Wasilewski et al have systematically investigated the hot spots with reliable experiment [29]. The formation mechanism of the hot spots was explained as the low resistance path caused by a local alloy separation in ternary layers, induced by floating organic molecules or molecular contamination clusters caused nanowire-like defects [29].…”

A passively mode-locked, self-starting femtosecond Yb:KYW laser with a single highly dispersive semiconductor double-chirped mirror for dispersion compensation

“…Experiments in a number of different MBE reactors have indicated that the Ga-related defects have higher impact on the mirror reflectivity than the misfit dislocations. It has also been demonstrated that a significant reduction of Ga-related defect density may be obtained by replacing the classical Ga effusion cell with the SUMO type cell [20,21].…”