1. Improved crystallographic order of ScAlN/GaN heterostructures grown at low temperatures under metal rich surface conditions.
- Author
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Motoki, Keisuke, Engel, Zachary, McCrone, Timothy M., Chung, Huijin, Matthews, Christopher M., Lee, Sangho, Marshall, Emily N., Ghosh, Aheli, Tang, Amanda, and Doolittle, W. Alan
- Subjects
METALS at low temperatures ,METALLIC surfaces ,GALLIUM nitride ,LATTICE constants ,HETEROSTRUCTURES ,VACUUM arcs ,COMPLEMENTARY metal oxide semiconductors - Abstract
Sc
0.18 Al0.82 N/GaN with state-of-the-art x-ray diffraction figures of merit grown by metal modulated epitaxy under metal-rich conditions and a low substrate temperature of 400 °C is demonstrated to have improved crystalline order [250 arc sec for the (0002) reflection and 469 arc sec for the (10 1 ¯ 5)] compared to a previous state-of-the-art sample grown at a more conventional temperature of 650 °C. While both samples show a columnar structure, the higher substrate temperature sample has a good symmetric rocking curve (RC) of 229 arc sec, but unlike the lower temperature sample, the RC of the (10 1 ¯ 5) asymmetric reflection could not be measured, indicating a more columnar structure common among ScAlN films. Local lattice constant maps (LLCMs) from 4D-STEM depict abrupt strain relaxation within ∼2 nm from the ScAlN/GaN interface for the sample grown at Tsub = 400 °C. Since these LLCMs suggest a lattice mismatch in the a-lattice constant, and since the films show a sudden roughening, the composition for lattice match to GaN may be less than the accepted 18%–20% Sc, consistent with the average GaN lattice match from lattice constant values reported in the literature of 12%. Compared to traditional III-Nitrides, ScAlN films have substantially more screw and mixed-type threading dislocations, suggesting substantial shear forces that result in significant twist and distortion leading to orthorhombic diffraction patterns as viewed from plan-view TEM in the Tsub = 650 °C sample. These results offer the possibility of ScAlN integration into low-thermal-budget processes including CMOS but further indicate that structural understanding of ScAlN remains lacking. [ABSTRACT FROM AUTHOR]- Published
- 2024
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