Low-Defect-Density Aluminum Nitride (AlN) Thin Films Realized by Zigzag Macrostep-Induced Dislocation Redirection

Abstract

Owing to the lack of large-diameter and affordable AlN bulk crystals, high-quality AlN films grown on sapphire substrates have been intensively analyzed for the potential applications in optoelectronic and electronic devices. Herein, we successfully fabricated low-defect-density AlN thin films on large-offcut-angle sapphire substrates combining magnetron sputtering and metal–organic chemical vapor deposition. It is found that the crystalline qualities of AlN films strongly depend on the densities and geometric features of atomic steps. When high-density zigzag macrosteps are formed on the surface, they can induce dislocation inclination toward multiple directions rather than a single one. In this situation, the inclined dislocations can interact with not only vertical dislocations but also other inclined dislocations. Profiting from the large inclination angles (30–78°), the lateral interaction range of dislocations exhibits a 6-fold increase at most, leading to more frequent dislocation interactions within a relatively thin layer. As a result, the threading dislocation density value of 1 μm thick AlN is reduced down to 1.4 × 109 cm–2, demonstrating an 80% decrease in comparison with its counterpart without the macrostep-induced dislocation redirection effect. This approach is expected to boost the development of low-cost and high-performance devices on AlN/sapphire templates.

Recent Advances in Fabricating Wurtzite AlN Film on (0001)-Plane Sapphire Substrate

“…Recently, our group has found that adopting large-offcut-angle sapphire substrate can significantly improve the crystalline quality of the AlN epilayer grown by the TSG technique [42]. The physical reason is macro-steps tend to appear on the large-offcut-angle sapphire substrate, and dislocations are easy to lock and drag by the edges of macro-steps, resulting in the inclination and interaction with other dislocations.…”

“…However, the stress control is still a problem for thick film due to the lack of stress-releasing channels. Reprinted with permission from [42]. Copyright {2021} American Chemical Society.…”

“…Thus, the AlN epilayer is nearly stress-free. [17,36,40,42,43,46,53,56,[58][59][60]62,69,73,74,76,79,81,94,[98][99][100][101][102][103][104][105][106][107][108][109] It is noted that there has been no unified standard for the evaluation of TDD. X-ray rocking curve (XRC) scan is the most common method to evaluate TDD.…”

“…Figure 6. (a-c) Bird's-eye-view and (d-f) plan-view schematic diagram of dislocation evolution for TSG-AlN with monoatomic step, straight macro-step, and zigzag macro-step morphologies.Reprinted with permission from[42]. Copyright {2021} American Chemical Society.…”

“…Figure 23. Selected AlN/sapphire TDD by year of publication[17,36,40,42,43,46,53,56,[58][59][60]62,69,73,74,76,79,81,94,[98][99][100][101][102][103][104][105][106][107][108][109]. The ultralow TDD value of 3.4 × 10 7 cm −2 has been achieved by ELOG growth technique in 2006.…”