Defect Structure Determination of GaN Films in GaN/AlN/Si Heterostructures by HR-TEM, XRD, and Slow Positrons Experiments

Vladimir Lucian Ene; Doru Dinescu; Nikolay Djourelov; Iulia Zai; Bogdan Stefan Vasile; Andreea Bianca Serban; Victor Leca; Ecaterina Andronescu

doi:10.3390/nano10020197

Defect Structure Determination of GaN Films in GaN/AlN/Si Heterostructures by HR-TEM, XRD, and Slow Positrons Experiments

Nanomaterials (Basel). 2020 Jan 23;10(2):197. doi: 10.3390/nano10020197.

Authors

Vladimir Lucian Ene^{1

2}, Doru Dinescu^{2

3}, Nikolay Djourelov², Iulia Zai^{2

4}, Bogdan Stefan Vasile¹, Andreea Bianca Serban^{2

3}, Victor Leca², Ecaterina Andronescu¹

Affiliations

¹ Department of Science and Engineering of Oxide Materials and Nanomaterials, Faculty of Applied Chemistry and Materials Science, University Politehnica of Bucharest, 060042 Bucharest, Romania.
² Extreme Light Infrastructure-Nuclear Physics (ELI-NP), 'Horia Hulubei' National R&D Institute for Physics and Nuclear Engineering (IFIN-HH), 30 Reactorului Street, 077125 Măgurele, Romania.
³ Doctoral School in Engineering and Applications of Lasers and Accelerators, University Politehnica of Bucharest, 060042 Bucharest, Romania.
⁴ Faculty of Physics, University of Bucharest, 077125 Măgurele, Romania.

Abstract

The present article evaluates, in qualitative and quantitative manners, the characteristics (i.e., thickness of layers, crystal structures, growth orientation, elemental diffusion depths, edge, and screw dislocation densities), within two GaN/AlN/Si heterostructures, that alter their efficiencies as positron moderators. The structure of the GaN film, AlN buffer layer, substrate, and their growth relationships were determined through high-resolution transmission electron microscopy (HR-TEM). Data resulting from high-resolution X-ray diffraction (HR-XRD) was mathematically modeled to extract dislocation densities and correlation lengths in the GaN film. Positron depth profiling was evaluated through an experimental Doppler broadening spectroscopy (DBS) study, in order to quantify the effective positron diffusion length. The differences in values for both edge (ρde) and screw (ρds) dislocation densities, and correlation lengths (L^e, L^s) found in the 690 nm GaN film, were associated with the better effective positron diffusion length (L_eff) of LeffGaN2 = 43 ± 6 nm.

Keywords: dislocations; epitaxial thin films; gallium nitride; positron diffusion length.