Browsing by Author "Bolukbas, B."

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    Improvement of breakdown characteristics in AlGaN/GaN/AlxGa 1-xN HEMT based on a grading Al xGa 1-xN buffer layer
    (Wiley, 2010-08-03) Yu, H.; Lisesivdin, S. B.; Ozturk, M.; Bolukbas, B.; Kelekci, O.; Ozturk, M. K.; Ozcelik, S.; Caliskan, D.; Cakmak, H.; Demirel, P.; Özbay, Ekmel
    To improve the breakdown characteristics of an AlGaN/GaN based high electron mobility transistor (HEMT) for high voltage applications, AlGaN/GaN/Al xGa 1-xN double heterostructure (DH-HEMTs) were designed and fabricated by replacing the semi-insulating GaN buffer with content graded Al xGa 1-xN (x=x 1 → x 2, x 1 > x 2), in turn linearly lowering the Al content x from x 1=90% to x 2=5% toward the front side GaN channel on a high temperature AlN buffer layer. The use of a highly resistive Al xGa 1-xN epilayer suppresses the parasitic conduction in the GaN buffer, and the band edge discontinuity limits the channel electrons spillover, thereby reducing leakage current and drain current collapse. In comparison with the conventional HEMT that use a semi-insulating GaN buffer, the fabricated DH-HEMT device with the same size presents a remarkable enhancement of the breakdown voltage.
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    ItemOpen Access
    Metalorganic chemical vapor deposition growth and thermal stability of the AllNN/GaN high electron mobility transistor structure
    (IOP Publishing, 2011) Yu, H.; Ozturk, M.; Demirel, P.; Cakmak, H.; Bolukbas, B.; Caliskan, D.; Özbay, Ekmel
    The AlxIn1-xN barrier high electron mobility transistor (HEMT) structure has been optimized with varied barrier composition and thickness grown by metalorganic chemical vapor deposition. After optimization, a transistor structure comprising a 7 nm thick nearly lattice-matched Al0.83In0.17 N barrier exhibits a sheet electron density of 2.0 x 10(13) cm(-2) with a high electron mobility of 1540 cm(2) V-1 s(-1). AnAl(0.83)In(0.17)N barrier HEMT device with 1 mu m gate length provides a current density of 1.0 A mm(-1) at V-GS = 0 V and an extrinsic transconductance of 242 mS mm(-1), which are remarkably improved compared to that of a conventional Al0.3Ga0.7N barrier HEMT. To investigate the thermal stability of the HEMT epi-structures, post-growth annealing experiments up to 800 degrees C have been applied to Al0.83In0.17N and Al0.3Ga0.7N barrier heterostructures. As expected, the electrical properties of an Al0.83In0.17N barrier HEMT structure showed less stability than that of an Al0.3Ga0.7N barrier HEMT to the thermal annealing. The structural properties of Al0.83In0.17N/GaN also showed more evidence for decomposition than that of the Al0.3Ga0.7N/GaN structure after 800 degrees C post-annealing.