title: Quantitative parameters for the examination of InGaN QW multilayers by low-loss EELS.
abstract: We present a detailed examination of a multiple InxGa1-xN quantum well (QW) structure for optoelectronic applications. The characterization is carried out using scanning transmission electron microscopy (STEM), combining high-angle annular dark field (HAADF) imaging and electron energy loss spectroscopy (EELS). Fluctuations in the QW thickness and composition are observed in atomic resolution images. The impact of these small changes on the electronic properties of the semiconductor material is measured through spatially localized low-loss EELS, obtaining band gap and plasmon energy values. Because of the small size of the InGaN QW layers additional effects hinder the analysis. Hence, additional parameters were explored, which can be assessed using the same EELS data and give further information. For instance, plasmon width was studied using a model-based fit approach to the plasmon peak; observing a broadening of this peak can be related to the chemical and structural inhomogeneity in the InGaN QW layers. Additionally, Kramers-Kronig analysis (KKA) was used to calculate the complex dielectric function (CDF) from the EELS spectrum images (SIs). After this analysis, the electron effective mass and the sample absolute thickness were obtained, and an alternative method for the assessment of plasmon energy was demonstrated. Also after KKA, the normalization of the energy-loss spectrum allows us to analyze the Ga 3d transition, which provides additional chemical information at great spatial resolution. Each one of these methods is presented in this work together with a critical discussion of their advantages and drawbacks.
authors: LENS-MIND-IN2UB, Laboratory of Electron NanoScopies, Departament d'Electrónica, Universitat de Barcelona, Barcelona, Spain. aeljarrat@el.ub.edu.
authors: Alberto
authors: A
authors: Eljarrat
authors: LENS-MIND-IN2UB, Laboratory of Electron NanoScopies, Departament d'Electrónica, Universitat de Barcelona, Barcelona, Spain. aeljarrat@el.ub.edu.
authors: Lluís
authors: L
authors: López-Conesa
authors: LMA-INA Laboratorio de Microscopías Avanzadas, Instituto de Nanociencia de Aragón - ARAID, Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50018 Zaragoza, Spain.
authors: César
authors: C
authors: Magén
authors: ISOM, Instituto de Sistemas Optoelectrónicos y Microtecnología, Universidad Politécnica de Madrid, Madrid, Spain.
authors: Noemí
authors: N
authors: García-Lepetit
authors: ISOM, Instituto de Sistemas Optoelectrónicos y Microtecnología, Universidad Politécnica de Madrid, Madrid, Spain.
authors: Žarko
authors: Ž
authors: Gačević
authors: ISOM, Instituto de Sistemas Optoelectrónicos y Microtecnología, Universidad Politécnica de Madrid, Madrid, Spain.
authors: Enrique
authors: E
authors: Calleja
authors: LENS-MIND-IN2UB, Laboratory of Electron NanoScopies, Departament d'Electrónica, Universitat de Barcelona, Barcelona, Spain. aeljarrat@el.ub.edu.
authors: Francesca
authors: F
authors: Peiró
authors: LENS-MIND-IN2UB, Laboratory of Electron NanoScopies, Departament d'Electrónica, Universitat de Barcelona, Barcelona, Spain. aeljarrat@el.ub.edu.
authors: Sònia
authors: S
authors: Estradé