Dr. Lei Tian Distinguished Lecture Series: Zlatko Sitar (NC State)

AlN – The Extreme Bandgap Semiconductor

AlN is an extreme bandgap material (Eg = 6.1 eV) with the potential to revolutionize not only UV and VUV optoelectronics but also high-power, high-frequency electronics. Although most challenges associated with the crystal growth and epitaxy of AlN have been overcome, achieving controlled electrical conductivity at technologically relevant levels has remained challenging. While controlling the chemical and electrochemical potentials during doping has been crucial for achieving control over doping and compensation, the resulting conductivity has remained modest. The presumed formation of the DX-1 defect has been regarded as a fundamental limitation because it pins the Fermi level and imposes a technologically limiting ceiling on the achievable free-carrier concentration.

We have developed several novel equilibrium and nonequilibrium approaches to doping and point-defect management in AlN and have demonstrated that donors in AlN do not undergo a DX-1 transition but instead are distributed between shallow and deep states. The shallow state can be kinetically stabilized, enabling highly conductive n-type AlN with carrier concentrations in the mid-1018 cm-3 range and high electron mobility. These results have enabled the first demonstration of AlN Schottky and p-n diodes capable of current densities exceeding 5 kAcm-2, with a critical breakdown field exceeding 12 MVcm-1 and stable operation at temperatures up to 700°C.

Bio: Zlatko Sitar is a Kobe Steel Distinguished Professor of materials science and engineering, physics, and electrical engineering at North Carolina State University. His research focuses on the growth and characterization of bulk and thin-film materials, property control, and device development in ultrawide- and extreme-bandgap semiconductors. He has developed and commercialized processes for the growth of AlN crystals, AlGaN epitaxy on AlN wafers, and doping control in these materials. Based on his research, he founded HexaTech, Inc., which focuses on AlN wafer technology, and Adroit Materials, Inc., which focuses on high-performance devices based on native GaN and AlN substrates for applications in the U.S. Department of Defense and NASA.