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

J M Mánuel; C T Koch; V B Özdöl; W Sigle; P A VAN Aken; R García; F M Morales

doi:10.1111/jmi.12312

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

J Microsc. 2015 Jan;261(1):27-35. doi: 10.1111/jmi.12312. Epub 2015 Sep 15.

Authors

J M Mánuel¹, C T Koch², V B Özdöl³, W Sigle⁴, P A VAN Aken⁴, R García¹, F M Morales¹

Affiliations

¹ IMEYMAT: Institute of Research on Electron Microscopy and Materials of the University of Cádiz, Cádiz, Spain.
² Department of Physics, Humboldt University, Berlin, Germany.
³ National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, U.S.A.
⁴ Stuttgart Center for Electron Microscopy, Max Planck Institute for Solid State Research, Germany.

PMID: 26372901
DOI: 10.1111/jmi.12312

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.

Keywords: Dark-field inline holography; InAlGaN; TEM; VEELS; nitride bandgap; strain.

Publication types

Research Support, Non-U.S. Gov't