Niobium-stress influence on Nb/Al-oxide/Nb trilayer Josephson-junction characteristics is studied. Different junction fabrication techniques are examined such as conventional etching and new lift-off processes. Nb-film stress, relaxed during trilayer etching, can deteriorate junction quality in etching-processed junctions smaller than a few micrometers square. Such deterioration does not occur in lift-off processed junctions even when they are 1 μm square because stress relaxation occurs during trilayer deposition through lift-off stencils. This new all-Nb Josephson-junction fabrication technique produces high-quality junctions with Rsg/Rnn =24 (Rsg and Rnn are tunnel resistances at 2 and 4 mV, respectively) and a current uniformity of 1.5% for 100 1-μm-square junctions connected in series.
The first direct modulation of a 1.3 mm-range metamorphic laser diode on a GaAs substrate has been realised. A 200 mm-long device had threshold currents as low as 5.2 and 11.4 mA at 25 and 858C, respectively. This laser also achieved 10 Gbit/s direct modulation up to 858C.Introduction: A 1.3 mm-range laser that can operate over a wide temperature range is an attractive light source, because it enables us to realise a low-cost module with low power consumption. The key to expanding the maximum operating temperature range is to reduce the carrier overflow from a multiple quantum well (MQW) at high temperatures. Lasers on GaAs substrates have cladding and barrier layers with large bandgaps, and this improves carrier confinement at high temperatures. Therefore, several approaches, including GaInNAs and InAs quantum dot techniques on a GaAs substrate, have been investigated with a view to realising 1.3 mm-range uncooled lasers.Another approach is to use a metamorphic buffer to lengthen the emission wavelength of an InGaAs MQW to 1.3 mm on a GaAs substrate. Metamorphic growth involves forming a buffer layer with a different lattice constant from that of the substrate by employing strain relaxation. 1.3 mm-range emissions from metamorphic InGaAs lasers have been reported [1][2][3]. In our previous study, we successfully formed a very flat and well-relaxed InGaAs layer on a GaAs substrate by using an abrupt InGaAs buffer instead of a graded buffer, and realised a laser with good static characteristics [4].In this work, we constructed a high performance short cavity FabryPerot laser with a metamorphic buffer. A highly strained InGaAsInGaAs MQW on a low indium content InGaAs buffer enables us to realise 1.3 mm-range lasing and low threshold current operation. This laser achieved a wide operating temperature range (25 -1358C) and uncooled 10 Gbit/s operation up to 858C.
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