Engineering High-Quality Crack-Free AlN on Si(111) by a Hybrid 3D/2D Growth Mode in MOCVD

Aluminum nitride (AlN) is a key wide-bandgap semiconductor for advanced technologies. However, the heteroepitaxial growth of high-quality AlN on Si(111) remains challenging due to significant lattice and thermal mismatches. Through a systematic optimization study of chamber pressure (5–75 kPa) and V/III ratios (110–13750), we establish that the material quality is critically dependent on a specific V/III regime: excessively low ratios lead to unmerged large plateaus, while excessively high ratios cause a sharp growth rate reduction and quality degradation. We further elucidate that low pressure facilitates smooth 2D growth, effectively suppressing screw dislocations, whereas high pressure promotes a 3D island-growth mode, enabling the effective release of tensile stress and the suppression of edge dislocations. By strategically combining these insights, we fabricated a 500 nm thick, crack-free AlN film using a hybrid 3D/2D approach. This method involves the initial deposition of a 100 nm thick 3D AlN layer under 50 kPa and a V/III ratio of 2750, followed by the growth of a 400 nm thick 2D AlN layer under 5 kPa and a V/III ratio of 550. The resultant film exhibits an atomically smooth surface with a root-mean-square (RMS) roughness of 0.36 nm, high crystallinity evidenced by X-ray diffraction rocking curve (XRC) full widths at half-maximum (fwhm) of 685.2 and 992.1 arcsec for the (002) and (102) planes, respectively, and relatively low residual tensile stress of 1.18 GPa. This work provides a robust and scalable pathway for the development of high-performance AlN-based devices on silicon platforms.