Microscopy and Microanalysis

Materials Applications

Optoelectronic Properties of InAlN/GaN Distributed Bragg Reflector Heterostructure Examined by Valence Electron Energy Loss Spectroscopy

A. Eljarrata1 c1, S. Estradéa1a4, Ž. Gačevića2, S. Fernández-Garridoa2a5, E. Callejaa2, C. Magéna3 and F. Peiróa1

a1 Laboratory of Electron NanoScopies, LENS-MIND-IN2UB, Dept. Electrónica, Universitat de Barcelona, Marti i Franqués 1, Barcelona, Spain

a2 ISOM, Instituto de Sistemas Optoelectrónicos y Microtecnología, Universidad Politécnica de Madrid, Spain

a3 Instituto de Nanociencia de Aragón (INA) and Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50018 Zaragoza, Spain. Fundación ARAID, 50018 Zaragoza, Spain

a4 TEM-MAT, (CCiT), Universitat de Barcelona, Solís i Sabarís 1, Barcelona, Spain

a5 Paul-Drude-Institute for Solid State Electronics, Hausvogteiplatz, 5-10117 Berlin, Germany

Abstract

High-resolution monochromated electron energy loss spectroscopy (EELS) at subnanometric spatial resolution and <200 meV energy resolution has been used to assess the valence band properties of a distributed Bragg reflector multilayer heterostructure composed of InAlN lattice matched to GaN. This work thoroughly presents the collection of methods and computational tools put together for this task. Among these are zero-loss-peak subtraction and nonlinear fitting tools, and theoretical modeling of the electron scattering distribution. EELS analysis allows retrieval of a great amount of information: indium concentration in the InAlN layers is monitored through the local plasmon energy position and calculated using a bowing parameter version of Vegard Law. Also a dielectric characterization of the InAlN and GaN layers has been performed through Kramers-Kronig analysis of the Valence-EELS data, allowing band gap energy to be measured and an insight on the polytypism of the GaN layers.

(Received January 16 2012)

(Accepted May 03 2012)

Key words

  • VEELS;
  • optical properties;
  • III-V nitrides;
  • Kramers-Kronig analysis;
  • band gap

Correspondence:

c1 Corresponding author. E-mail: aeljarrat@el.ub.edu