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Michalas L.,National and Kapodistrian University of Athens | Koutsoureli M.,National and Kapodistrian University of Athens | Papaioannou G.J.,National and Kapodistrian University of Athens | Stavrinidis G.,Microelectronics Research Group MRG | Konstantinidis G.,Microelectronics Research Group MRG
European Microwave Week 2012: "Space for Microwaves", EuMW 2012, Conference Proceedings - 7th European Microwave Integrated Circuits Conference, EuMIC 2012 | Year: 2012

The present paper investigates for the first time the electrical properties of dielectric less and dimple less MEMS capacitive switches. The capacitance of these devices increases rapidly beyond pull-in being proportional to the Fowler-Nordhein current-voltage relation. The study is carried out through experimentally obtained capacitance- and current-voltage characteristic that agree with the corresponding capacitance and field emission current models. © 2012 European Microwave Assoc.


Adikimenakis A.,Microelectronics Research Group MRG | Adikimenakis A.,University of Crete | Aretouli K.E.,Microelectronics Research Group MRG | Aretouli K.E.,University of Crete | And 6 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2013

The mechanism of Si outdiffusion related to the formation of Si-rich GaN clusters during the growth of GaN-on-Si by plasma-assisted molecular beam epitaxy (PAMBE) has been identified. GaN thin films were grown, on high resistivity Si (111) substrates at Ga-rich conditions to favour the 2D step-flow growth mode. Hall-effect measurements revealed very high electron background concentrations, ranging from 2 x 1018 cm-3 to 3 x 1019 cm-3, with degraded carrier mobility in the range of 5-30 cm2/Vs. SEM examination of surfaces and cross-sections of the samples revealed the presence of hollow GaN clusters on the film surface and voids at the Si/III-nitride interface. EDX spot analysis revealed dissolution of Si material in the GaN clusters. Growth of GaN on Si under stoichiometric conditions resulted in films without GaN clusters, which exhibited a serious reduction in carrier concentration, down to 1.4 x 1016 cm-3, with a simultaneous increase of the carrier mobility to 137 cm2/Vs. C-V carrier profile measurements were consistent with Hall-effect measurements and revealed a uniform electron concentration in the GaN film, down to the AlN nucleation layer. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Bazioti C.,Aristotle University of Thessaloniki | Papadomanolaki E.,Microelectronics Research Group MRG | Papadomanolaki E.,University of Crete | Kehagias T.,Aristotle University of Thessaloniki | And 8 more authors.
Journal of Applied Physics | Year: 2015

We investigate the structural properties of a series of high alloy content InGaN epilayers grown by plasma-assisted molecular beam epitaxy, employing the deposition temperature as variable under invariant element fluxes. Using transmission electron microscopy methods, distinct strain relaxation modes were observed, depending on the indium content attained through temperature adjustment. At lower indium contents, strain relaxation by V-pit formation dominated, with concurrent formation of an indium-rich interfacial zone. With increasing indium content, this mechanism was gradually substituted by the introduction of a self-formed strained interfacial InGaN layer of lower indium content, as well as multiple intrinsic basal stacking faults and threading dislocations in the rest of the film. We show that this interfacial layer is not chemically abrupt and that major plastic strain relaxation through defect introduction commences upon reaching a critical indium concentration as a result of compositional pulling. Upon further increase of the indium content, this relaxation mode was again gradually succeeded by the increase in the density of misfit dislocations at the InGaN/GaN interface, leading eventually to the suppression of the strained InGaN layer and basal stacking faults. © 2015 AIP Publishing LLC.


Kuzmik J.,Slovak Academy of Sciences | Hascik S.,Slovak Academy of Sciences | Kucera M.,Slovak Academy of Sciences | Kudela R.,Slovak Academy of Sciences | And 7 more authors.
Applied Physics Letters | Year: 2015

0.5-1 μm thick InN {0001} films grown by molecular-beam epitaxy with N- or In-polarity are investigated for the presence of native oxide, surface energy band bending, and effects introduced by 2 to 4 monolayers of GaN capping. Ex situ angle-resolved x-ray photo-electron spectroscopy is used to construct near-surface (GaN)/InN energy profiles, which is combined with deconvolution of In3d signal to trace the presence of InN native oxide for different types of polarity and capping. Downwards surface energy band bending was observed on bare samples with native oxide, regardless of the polarity. It was found that the In-polar InN surface is most readily oxidized, however, with only slightly less band bending if compared with the N-polar sample. On the other hand, InN surface oxidation was effectively mitigated by GaN capping. Still, as confirmed by ultra-violet photo-electron spectroscopy and by energy band diagram calculations, thin GaN cap layer may provide negative piezoelectric polarization charge at the GaN/InN hetero-interface of the N-polar sample, in addition to the passivation effect. These effects raised the band diagram up by about 0.65 eV, reaching a flat-band profile. © 2015 AIP Publishing LLC.

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