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Polarization induced doping in graded AlxGa1xN / submitted by Anna Theresa Steiner, BSc
AutorInnenSteiner, Anna Theresa
Beurteiler / BeurteilerinBonanni, Alberta ; Böhm, Helga
ErschienenLinz, 2018
Umfangx, 76 Seiten : Illustrationen
HochschulschriftUniversität Linz, Masterarbeit, 2018
URNurn:nbn:at:at-ubl:1-24843 Persistent Identifier (URN)
 Das Werk ist gemäß den "Hinweisen für BenützerInnen" verfügbar
Polarization induced doping in graded AlxGa1xN [21.51 mb]

The wide band-gap semiconductor AlxGa1xN is the material system of choice for optoelectronic applications in the middle and deep ultraviolet (DUV). However, a major issue in realizing these functional devices comes from the challenges related to the efficient n- and p-type doping of AlxGa1xN with Al content x > 0.6, primarily due to the high activation energies of the acceptors and donors. In addition, compensation effects due to deep level acceptors or donors are detrimental for obtaining optimum conductivity in both p- and n-type AlxGa1xN. In this work, an alternative approach to impurity doping AlxGa1xN by utilizing the high spontaneous and piezoelectric polarization fields in wurtzite III-nitrides is proposed. Layers of AlxGa1xN with compositionally graded Al content 0.6 > x > 0.25 are fabricated, to stabilize a three dimensional electron gas. The AlxGa1xN-based structures analyzed are grown on c-plane Al2O3 wafers in a metal organic vapor phase epitaxy reactor and their structural, chemical and electrical properties are studied in-depth. Four main structures are analyzed, namely: (a) reference AlxGa1xN, (b) reference AlxGa1xN:Si grown on an AlxGa1xN buffer, (c) and (d): graded AlxGa1xN on AlxGa1xN and on AlxGa1xN:Si, respectively. The surface morphology of the grown samples - investigated using atomic force microscopy - reveals a surface roughness up to 3.2nm, while high resolution x-ray diffraction and transmission electron microscopy provide information on the high crystalline quality of the grown structures. The chemical characterization of the fabricated samples is carried out by using x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy. In-depth electrical transport studies including low temperature Hall effect measurements are performed and a carrier concentration of 9.3 · 10 18 cm3 for a surface Al concentration of (42.5 2.6)% is achieved in the graded AlxGa1xN. The use of polarization effects to increase the conductivity in an AlxGa1xN structure with high Al concentration is a novel approach which allows to overcome the limitation of direct impurity doping and promises to further extend the already broad area of applications of AlxGa1xN-structures.

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