A solid-state NMR and DFT study of compositional modulations in AlxGa1-xAs

Autor(en)

Paulus J. Knijn, P. Jan M. van Bentum, Ernst R. H. van Eck, Changming Fang, Dennis L. A. G. Grimminck, Robert A. de Groot, Remco W. A. Havenith, Martijn Marsman, Leo Meerts, Gilles de Wijs, Arno P. M. Kentgens

Abstrakt

We have conducted As-75 and Ga-69 Nuclear Magnetic Resonance (NMR) experiments to investigate order/disorder in AlxGa1-xAs lift-off films with x similar to 0.297 and 0.489. We were able to identify all possible As(AlnGa4-n) sites with n = 0-4 coordinations in As-75 NMR spectra using spin-echo experiments at 18.8 Tesla. This was achieved by employing high rf field strengths using a small solenoid coil and an NMR probe specifically designed for this purpose. Spectral deconvolution, using an evolutionary algorithm, complies with the absence of long-range order if a CuAu based order parameter is imposed. An unconstrained fit shows a deviation of the statistics imposed by this type of ordering. The occupational disorder in the Ga and Al positions is reflected in a distribution of the Electric Field Gradients (EFGs) experienced at the different arsenic sites. We established that this can be modelled by summing the effects of the first coordination sphere and a Czjzek type distribution resulting from the compositional variation in the Al/Ga sub-lattice in the higher coordination spheres. Ga-69 3QMAS and nutation data exclude the presence of highly symmetric sites and also show a distribution in EFG. The experimentally obtained quadrupolar interactions are in good agreement with calculations based on Density Functional Theory (DFT). Using additivity of EFG tensors arising from distant charge perturbations, we could use DFT to model the EFG distributions of the n = 0-4 sites, reproducing the Czjzek and extended Czjzek distributions that were found experimentally. On the basis of these calculations we conclude that the As-75 quadrupolar interaction is sensitive to compositional modulations up to the 7th coordination shell in these systems.

Organisation(en)

Computergestützte Materialphysik

Externe Organisation(en)

Radboud University

Journal

Physical Chemistry Chemical Physics

Band

12

Seiten

11517-11535

Anzahl der Seiten

19

ISSN

1463-9076

DOI

https://doi.org/10.1039/C003624B

Publikationsdatum

2010

Peer-reviewed

Ja

ÖFOS 2012

103018 Materialphysik

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/5db99373-9a35-4b64-8f29-856dd4403d73