title: Nanoscale Electrostructural Characterization of Compositionally Graded Al(x)Ga(1-x)N Heterostructures on GaN/Sapphire (0001) Substrate.
abstract: We report on AlxGa1-xN heterostructures resulting from the coherent growth of a positive then a negative gradient of the Al concentration on a [0001]-oriented GaN substrate. These polarization-doped p-n junction structures were characterized at the nanoscale by a combination of averaging as well as depth-resolved experimental techniques including: cross-sectional transmission electron microscopy, high-resolution X-ray diffraction, Rutherford backscattering spectrometry, and scanning probe microscopy. We observed that a small miscut in the substrate orientation along with the accumulated strain during growth led to a change in the mosaic structure of the AlxGa1-xN film, resulting in the formation of macrosteps on the surface. Moreover, we found a lateral modulation of charge carriers on the surface which were directly correlated with these steps. Finally, using nanoscale probes of the charge density in cross sections of the samples, we have directly measured, semiquantitatively, both n- and p-type polarization doping resulting from the gradient concentration of the AlxGa1-xN layers.
authors.affiliation: Institute for Nanoscience and Engineering, University of Arkansas , West Dickson 731, Fayetteville, Arkansas 72701, United States.|V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine , Pr. Nauky 41, 03680 Kyiv, Ukraine.
authors.forename: Andrian V
authors.initials: AV
authors.lastname: Kuchuk
authors.affiliation: V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine , Pr. Nauky 41, 03680 Kyiv, Ukraine.
authors.forename: Petro M
authors.initials: PM
authors.lastname: Lytvyn
authors.affiliation: Institute for Nanoscience and Engineering, University of Arkansas , West Dickson 731, Fayetteville, Arkansas 72701, United States.
authors.forename: Chen
authors.initials: C
authors.lastname: Li
authors.affiliation: V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine , Pr. Nauky 41, 03680 Kyiv, Ukraine.
authors.forename: Hryhorii V
authors.initials: HV
authors.lastname: Stanchu
authors.affiliation: Institute for Nanoscience and Engineering, University of Arkansas , West Dickson 731, Fayetteville, Arkansas 72701, United States.
authors.forename: Yuriy I
authors.initials: YI
authors.lastname: Mazur
authors.affiliation: Institute for Nanoscience and Engineering, University of Arkansas , West Dickson 731, Fayetteville, Arkansas 72701, United States.
authors.forename: Morgan E
authors.initials: ME
authors.lastname: Ware
authors.affiliation: Institute for Nanoscience and Engineering, University of Arkansas , West Dickson 731, Fayetteville, Arkansas 72701, United States.
authors.forename: Mourad
authors.initials: M
authors.lastname: Benamara
authors.affiliation: National Centre for Nuclear Research , ul. Andrzeja Sołtana 7, 05-400 Otwock, Poland.
authors.forename: Renata
authors.initials: R
authors.lastname: Ratajczak
authors.affiliation: Institute for Nanoscience and Engineering, University of Arkansas , West Dickson 731, Fayetteville, Arkansas 72701, United States.
authors.forename: Vitaliy
authors.initials: V
authors.lastname: Dorogan
authors.affiliation: V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine , Pr. Nauky 41, 03680 Kyiv, Ukraine.
authors.forename: Vasyl P
authors.initials: VP
authors.lastname: Kladko
authors.affiliation: V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine , Pr. Nauky 41, 03680 Kyiv, Ukraine.
authors.forename: Alexander E
authors.initials: AE
authors.lastname: Belyaev
authors.affiliation: Institute for Nanoscience and Engineering, University of Arkansas , West Dickson 731, Fayetteville, Arkansas 72701, United States.
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Salamo
keywords: AlxGa1−xN; charge accumulation; graded layers; polarization doping; step-bunching effect; threading dislocations