Semiconductor Review: Specials Magazine

Why is bulk AlN industrialization critical for ultra-wide bandgap semiconductors? Industrializing bulk aluminum nitride (AlN) single-crystal substrates is one of the most technically demanding challenges in the ultra-wide bandgap (UWBG) semiconductor field. Ultratrend Technologies was founded in 2018 to address this challenge directly, focusing on bringing bulk AlN substrates into real device manufacturing. Headquartered in Hangzhou, the high-tech company was established by senior semiconductor experts who recognized that the future of UWBG electronics depends on substrate materials capable of sustaining extreme electrical, thermal and environmental demands. Rather than treating AlN as an experimental material, Ultratrend built full fabrication capability from the outset. Its scope spans reactor and hotzone design, modeling and simulation, process optimization, crystal growth, wafering and material characterization. Ultratrend has more than 60 patents applied for and granted, reflecting the depth of proprietary knowledge embedded across its technology stack. “Bulk AlN growth is not only about producing crystals, but about ensuring they can be consistently adopted in real device manufacturing,” says Dr. Liang Wu, Founder and CEO. Mastering Bulk AlN Growth What technical barriers define scalable bulk AlN crystal growth? AIN occupies a distinctive position within the UWBG semiconductor family. With an ultra-wide bandgap of 6.2 eV, an exceptionally high critical breakdown field, high thermal conductivity and semi-insulating resistivity, AlN ranks among the top when compared with emerging UWBG materials. These characteristics position it as a foundational substrate for deep-ultraviolet optoelectronics, high-power and high-frequency RF devices and next-generation power electronics. However, translating these intrinsic advantages into manufacturable substrates remains complex. Bulk AlN growth requires extreme thermal conditions and precise control of carbon and oxygen impurities, which directly impact DUV transparency. Ultratrend’s differentiation lies in how it addresses these challenges at system and process levels. The company has strategically adopted tungsten-based growth systems to minimize carbon and oxygen contamination, combined with homoepitaxial growth pathways to maintain crystal integrity. This strategy is supported by a multidisciplinary R&D team spanning materials science, computational modeling and equipment engineering. Ultratrend’s proprietary finite-element simulation platform integrates flow and mass transfer modeling, impurity transport, supersaturation control and three-dimensional stress prediction. These tools are embedded in equipment and process design to shorten development cycles and reduce growth risk. Multiple generations of fully automated physical vapor transport growth reactors, incorporating tailored hotzones and proprietary processes, have enabled stable material transport and suppression of parasitic nucleation. The outcome is consistent production of high-structural-quality AlN crystals with industry-leading deep-UV transparency. In 2024, Ultratrend introduced 2-inch high-transparency bulk AlN substrates demonstrating absorption coefficients of 7.2–10.7 cm⁻¹ in the 220–240 nm range and as low as 6.1 cm⁻¹ at 265 nm. For the first time, 2-inch PVT-grown AlN substrates achieved DUV transmittance comparable to HVPE-AlN, marking a significant milestone in bulk crystal growth..