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Regular version of the site

Article

Stress control in thick AlN/c-Al2O3 templates grown by plasma-assisted molecular beam epitaxy

Semiconductor Science and Technology. 2021. Vol. 36. No. 3.
Koshelev O., Nechaev D., Brunkov P., Ivanov S., Jmerik V.

Stress evolution was studied in up to similar to 3 mu m thick AlN templates, comprising similar to 65 nm thick AlN nucleation layers (NLs) and thick buffer layers (BLs), grown using different growth modes and conditions by plasma-assisted molecular beam epitaxy (PA MBE) on c-Al2O3. Growth of both the NL and BL in a standard PA MBE mode at N-rich conditions (at flux ratio Al/N-2* similar to 0.5) led to instant generation of a relatively high tensile stress (similar to 1.5 GPa) which is maintained throughout the entire growth. On the contrary, NLs, grown using a migration-enhanced epitaxy (MEE), demonstrated a transition from the initial compressive stress to stress-free growth, which is usually observed in the Volmer-Weber films. Further growth of thick AlN BLs on the MEE-NLs at various Al/N-2* ratios revealed a wide variety of stress evolution processes. The BL growth by using metal-modulated epitaxy (MME) at Me-rich conditions with Al/N-2* similar to 1.33 led to a gradual decrease in the initial compressive stress in the 2D AlN layers, whereas standard PA MBE growth of 3D BL at N-rich conditions (Al/N-2* similar to 0.92) exhibited a fast transition from the initial compressive stress to tensile stress. Moreover, we succeeded in achieving the quasi-stress-free growth of a 3.1 mu m thick AlN BL using the MME growth mode at the optimum flux ratio Al/N-2* = 1.05. These results were compared with the results of other authors and explained using a kinetic approach to description of stress evolution during PA MBE of AlN/c-Al2O3 templates, taking into account several simultaneously acting competitive mechanisms of continuous generation of tensile and compressive stresses.