title: Near-field imaging and spectroscopy of locally strained GaN using an IR broadband laser.
abstract: Scattering-type scanning near-field optical microscopy (SNOM) offers the possibility to analyze material properties like strain in crystals at the nanoscale. In this paper we introduce a SNOM setup employing a newly developed tunable broadband laser source with a covered spectral range from 9 µm to 16 µm. This setup allows for the first time optical analyses of the crystal structure of gallium nitride (GaN) at the nanometer scale by excitation of a near-field phonon resonance around 14.5 µm. On the example of an artificially induced stress field within a GaN wafer, we present a method for a 2D visualization of small deviations in the crystal structure, which allows for fast qualitative characterizations. Subsequently, the stress levels at chosen points were quantified by recording complex near-field spectra and correlating them with theoretical model calculations. Applied to the cross-section of a heteroepitaxially grown GaN wafer, we finally demonstrate the capability of our setup to analyze the relaxation of the crystal structure along the growth axis with a nanometer spatial resolution.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Bensmann
authors.forename: Fabian
authors.initials: F
authors.lastname: Gaußmann
authors.forename: Martin
authors.initials: M
authors.lastname: Lewin
authors.forename: Jochen
authors.initials: J
authors.lastname: Wüppen
authors.forename: Sebastian
authors.initials: S
authors.lastname: Nyga
authors.forename: Christoph
authors.initials: C
authors.lastname: Janzen
authors.forename: Bernd
authors.initials: B
authors.lastname: Jungbluth
authors.forename: Thomas
authors.initials: T
authors.lastname: Taubner
mesh_terms: D003952:Diagnostic Imaging; D004867:Equipment Design; D005708:Gallium / Q000737:chemistry*; D006801:Humans; D007834:Lasers; D008027:Light; D018625:Microscopy, Atomic Force / Q000295:instrumentation*; D008962:Models, Theoretical; D060739:Phonons; D013055:Spectrophotometry, Infrared
chemical_list: C473348:gallium nitride; D005708:Gallium