Work

Optimization of TMAl preflow for low temperature grown AlN for AlGaN UVC LED heterostructure

Year: 2026

Type: article

Abstract: High material quality aluminium nitride (AlN) layers are typically achievable at high growth temperatures of above 1200 °C. However, this growth method requires a specialized heater that is not available in most standard reactors. The present study demonstrates that comparable material quality of AlN layers, as obtained at high growth temperatures, can be achieved at 1175 °C. In particular, the study focuses on reducing threading dislocation density (TDD) in AlN layers, a critical factor in achieving high material quality, by introducing a trimethylaluminium (TMAl) preflow during the AlN growth. The TMAl preflow was introduced after AlN nucleation for 10, 20, 30, 45 and 60 s. An AlN layer grown without TMAl preflow was also included as a reference sample for comparison. The results revealed that the reference sample (without TMAl preflow) exhibited grainy surface, i.e., three-dimensional (3D) nanocolumns, with a TDD of 2.22 × 10 9 cm −2 . With the introduction of TMAl preflow for up to 30 s, the surface became significantly smoother with the absence of grains, while the TDD reduced to 1.57 × 10 9 cm −2 . The results indicate that the TMAl preflow can prevent the evolution of the co-existence of N-polar growth in the AlN growth which typically leads to the 3D nanocolumns formation. Additionally, 3D growth or islands formed after the nucleation can be enlarged by the TMAl preflow, allowing more threading dislocations (TDs) to incline toward the slanted facets of the islands during the AlN layer growth, increasing the possibility of their mutual annihilation. Meanwhile, an extension of the TMAl preflow duration beyond 30 s may facilitate carbon-rich clusters, which in turn increased the surface roughness, as characterized by the presence of 3D nanocolumns with facetted structure, and generated additional TDs. From cathodoluminescence (CL) spectra, an AlGaN UVC LED heterostructure grown on the AlN layer with 30 s of TMAl preflow (TDD = 1.57 × 10 9 cm −2 ) showed FWHM at ∼18 nm, slightly higher than that of a similar AlGaN UVC LED grown on a high temperature grown AlN layer above 1200 °C (FWHM = ∼14 nm) with a TDD of 9.33 × 10 8 cm −2 . Overall, this study demonstrates that the TMAl preflow with the optimized duration is beneficial for improving the AlN growth even at a temperature below 1200 °C, enabling the AlN to serve as a suitable base layer for UVC LEDs.

Source: Materials Science in Semiconductor Processing

DOI: 10.1016/j.mssp.2026.111214

Authors: Noratiqah Yusop, Muhammad Esmed Alif Samsudin, Yusnizam Yusuf, Mohd Nazri Abdul Rahman, Norzaini Zainal

Institution: Universiti Sains Malaysia

Language: English

Topic: GaN-based semiconductor devices and materials

Subfield: Condensed Matter Physics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $3,540

Funders: Nippon Sheet Glass Foundation for Materials Science and Engineering, Ministry of Higher Education, Malaysia