title: Inline electron holography and VEELS for the measurement of strain in ternary and quaternary (In,Al,Ga)N alloyed thin films and its effect on bandgap energy.
abstract: We present the use of (1) dark-field inline electron holography for measuring the structural strain, and indirectly obtaining the composition, in a wurtzite, 4-nm-thick InAlGaN epilayer on a AlN/GaN/AlN/GaN multinano-layer heterosystem, and (2) valence electron energy-loss spectroscopy to study the bandgap value of five different, also hexagonal, 20-50-nm-thick InAlGaN layers. The measured strain values were almost identical to the ones obtained by other techniques for similarly grown materials. We found that the biaxial strain in the III-N alloys lowers the bandgap energy as compared to the value calculated with different known expressions and bowing parameters for unstrained layers. By contrast, calculated and experimental values agreed in the case of lattice-matched (almost unstrained) heterostructures.
authors.affiliation: IMEYMAT: Institute of Research on Electron Microscopy and Materials of the University of Cádiz, Cádiz, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Mánuel
authors.affiliation: Department of Physics, Humboldt University, Berlin, Germany.
authors.forename: C T
authors.initials: CT
authors.lastname: Koch
authors.affiliation: National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, U.S.A.
authors.forename: V B
authors.initials: VB
authors.lastname: Özdöl
authors.affiliation: Stuttgart Center for Electron Microscopy, Max Planck Institute for Solid State Research, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Sigle
authors.affiliation: Stuttgart Center for Electron Microscopy, Max Planck Institute for Solid State Research, Germany.
authors.forename: P A
authors.initials: PA
authors.lastname: VAN Aken
authors.affiliation: IMEYMAT: Institute of Research on Electron Microscopy and Materials of the University of Cádiz, Cádiz, Spain.
authors.forename: R
authors.initials: R
authors.lastname: García
authors.affiliation: IMEYMAT: Institute of Research on Electron Microscopy and Materials of the University of Cádiz, Cádiz, Spain.
authors.forename: F M
authors.initials: FM
authors.lastname: Morales
keywords: Dark-field inline holography; InAlGaN; TEM; VEELS; nitride bandgap; strain