Strain-stress study of AlxGa1-xN/AlN heterostructures on c-plane sapphire and related optical properties

Yining Feng; Vishal Saravade; Ting-Fung Chung; Yongqi Dong; Hua Zhou; Bahadir Kucukgok; Ian T Ferguson; Na Lu

doi:10.1038/s41598-019-46628-4

Strain-stress study of Al_xGa_1-xN/AlN heterostructures on c-plane sapphire and related optical properties

Sci Rep. 2019 Jul 15;9(1):10172. doi: 10.1038/s41598-019-46628-4.

Authors

Yining Feng^{1

2}, Vishal Saravade³, Ting-Fung Chung¹, Yongqi Dong^{4

5}, Hua Zhou⁵, Bahadir Kucukgok^{1

2}, Ian T Ferguson^{6

7}, Na Lu^{8

9}

Affiliations

¹ Lyles School of Civil Engineering, Birck Nanotechnology Center, Purdue University, West Lafayette, IN, 47907, USA.
² Applied Materials Division, Argonne National Laboratory, 9700 South Cass Ave, Lemont, IL, 60439, USA.
³ Electrical and Computer Engineering, Missouri University of Science and Technology, Rolla, MO, 65409, USA.
⁴ National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, 230026, China.
⁵ Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Ave, Lemont, IL, 60439, USA.
⁶ Electrical and Computer Engineering, Missouri University of Science and Technology, Rolla, MO, 65409, USA. ianf@mst.edu.
⁷ Southern Polytechnic College of Engineering and Engineering Technology, Kennesaw State University, Marietta, GA, 30060, USA. ianf@mst.edu.
⁸ Lyles School of Civil Engineering, Birck Nanotechnology Center, Purdue University, West Lafayette, IN, 47907, USA. luna@purdue.edu.
⁹ School of Materials Engineering, Purdue University, West Lafayette, IN, 47907, USA. luna@purdue.edu.

Abstract

This work presents a systematic study of stress and strain of Al_xGa_1-xN/AlN with composition ranging from GaN to AlN, grown on a c-plane sapphire by metal-organic chemical vapor deposition, using synchrotron radiation high-resolution X-ray diffraction and reciprocal space mapping. The c-plane of the Al_xGa_1-xN epitaxial layers exhibits compressive strain, while the a-plane exhibits tensile strain. The biaxial stress and strain are found to increase with increasing Al composition, although the lattice mismatch between the Al_xGa_1-xN and the buffer layer AlN gets smaller. A reduction in the lateral coherence lengths and an increase in the edge and screw dislocations are seen as the Al_xGa_1-xN composition is varied from GaN to AlN, exhibiting a clear dependence of the crystal properties of Al_xGa_1-xN on the Al content. The bandgap of the epitaxial layers is slightly lower than predicted value due to a larger tensile strain effect on the a-axis compared to the compressive strain on the c-axis. Raman characteristics of the Al_xGa_1-xN samples exhibit a shift in the phonon peaks with the Al composition. The effect of strain on the optical phonon energies of the epitaxial layers is also discussed.