Strain relaxation and dislocation annihilation in compositionally graded α-(AlxGa1-x)2O3 layer for high voltage α-Ga2O3 power devices. (December 2021)

• Record Type: Journal Article
• Authors: Kim, Byungsoo; Yang, Duyoung; Sohn, Woonbae; Lee, Seungmin; Choi, Hwan-Hee-Chan; Jang, Taehoon; Yoon, Euijoon; Park, Yongjo; Jang, Ho Won
• Is Part Of: Acta materialia. Volume 221(2021)
• Publication Date: 2021-12
• Subjects: Gallium oxide -- Epitaxial growth -- Single crystalline -- Lattice strain -- Dislocation annihilation -- Schottky diode; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2021.117423
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: α-Ga2 O3 of the corundum structure and the large bandgap of 5.3 eV has attracted great interest because it can be grown on a sapphire (α-Al2 O3 ) substrate with the same crystal structure. However, the lattice mismatch (4.3%) and the different thermal expansion coefficients between α-Ga2 O3 and the sapphire substrate induce crystalline defects and thermal strain, leading to a high density of threading dislocations and degraded electrical properties of the α-Ga2 O3 films grown directly on the substrate. Herein, to circumvents these issues, compositionally graded α-(Alx Ga1-x )2 O3 layers are adopted to reduce threading dislocations for a high quality of epitaxial α-Ga2 O3 films. The evolution of strain relaxation and the inclination of threading dislocations in graded α-(Alx Ga1-x )2 O3 layers are confirmed by reciprocal space mapping (RSM) and transmission electron microscopy (TEM). Through RSM and TEM studies, we confirmed that compressive strain enhances the inclination of dislocations, and therefore, the dislocations merge and annihilate in the graded α-(Alx Ga1-x )2 O3 layers. Moreover, owing to dislocations annihilation in the graded α-(Alx Ga1-x )2 O3 layers, the calculated density of threading dislocations in α-Ga2 O3 films with a graded α-(Alx Ga1-x )2 O3 layer is reduced by 64.9% compared with that of α-Ga2 O3 films deposited directly grown on a bare sapphire substrate. Furthermore, a fabricated lateral-structure Schottky diodes reveals enhanced breakdown voltages and forward current density due to the improved crystalline quality using the graded α-(Alx Ga1-x )2 O3 layer. This study provides an attractive approach for obtaining high-quality epitaxial α-Ga2 O3 thin films for high voltage power devices. Graphical abstract: Image, graphical abstract