Browsing by Author "Ozcelik, S."

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    Investigation of AlInN HEMT structures with different AlGaN buffer layers grown on sapphire substrates by MOCVD
    (2012-01-01) Kelekçi, Özgür; Tasli, P.; Cetin, S.S.; Kasap, M.; Ozcelik, S.; Ozbay, E.
    We investigate the structural and electrical properties of AlxIn1exN/AlN/GaN heterostructures with AlGaN buffers grown by MOCVD, which can be used as an alternative to AlInN HEMT structures with GaN buffer. The effects of the GaN channel thickness and the addition of a content graded AlGaN layer to the structural and electrical characteristics were studied through variable temperature Hall effect measurements, high resolution XRD, and AFM measurements. Enhancement in electron mobility was observed in two of the suggested AlxIn1 xN/AlN/GaN/Al0.04Ga0.96N heterostructures when compared to the standard AlxIn1exN/AlN/GaN heterostructure. This improvement was attributed to better electron confinement in the channel due to electric field arising from piezoelectric polarization charge at the Al0.04Ga0.96N/GaN heterointerface and by the conduction band discontinuity formed at the same inter face. If the growth conditions and design parameters of the AlxIn1 xN HEMT structures with AlGaN buffers can be modified further, the electron spillover from the GaN channel can be significantly limited and even higher electron mobilities, which result in lower two-dimensional sheet resistances, would be possible.
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    Numerical optimization of In-mole fractions and layer thicknesses in AlxGa1 xN/AlN/GaN high electron mobility transistors with InGaN back barriers
    (2011-01-01) Lisesivdin, S.B.; Kelekçi, Özgür; Ozcelik, S.; Ozbay, E.
    The effects of the In-mole fraction (x) of an InxGa1 xN back barrier layer and the thicknesses of different layers in pseudomorphic AlyGa1 yN/AlN/GaN/InxGa1 xN/GaN heterostructures on band structures and carrier densities were investigated with the help of one-dimensional self-consistent solutions of non linear Schrodinger–Poisson equations. Strain relaxation limits were also calculated for the investigated ¨ AlyGa1 yN barrier layer and InxGa1 xN back barriers. From an experimental point of view, two different optimized structures are suggested, and the possible effects on carrier density and mobility are discussed.