Polarization-Engineered Enhancement-Mode High-Electron-Mobility Transistors Using Quaternary AlInGaN Barrier Layers

• Published in: Journal of electronic materials 2013-05, Vol.42 (5), p.826-832
• Main Authors: Reuters, Benjamin, Wille, A., Ketteniss, N., Hahn, H., Holländer, B., Heuken, M., Kalisch, H., Vescan, A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Dielectric thin films; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Electrical engineering; Electronics; Electronics and Microelectronics; Exact sciences and technology; Instrumentation; Materials; Materials Science; Optical and Electronic Materials; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Solid State Physics; Tensile strength; Transistors
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-013-2473-7

Group III nitride heterostructures with low polarization difference recently moved into the focus of research for realization of enhancement-mode (e-mode) transistors. Quaternary AlInGaN layers as barriers in GaN-based high-electron-mobility transistors (HEMTs) offer the possibility to perform polarization engineering, which allows control of the threshold voltage over a wide range from negative to positive values by changing the composition and strain state of the barrier. Tensile-strained AlInGaN layers with high Al contents generate high two-dimensional electron gas (2DEG) densities, due to the large spontaneous polarization and the contributing piezoelectric polarization. To lower the 2DEG density for e-mode HEMT operation, the polarization difference between the barrier and the GaN buffer has to be reduced. Here, two different concepts are discussed. The first is to generate compressive strain with layers having high In contents in order to induce a positive piezoelectric polarization compensating the large negative spontaneous polarization. Another novel approach is a lattice-matched Ga-rich AlInGaN/GaN heterostructure with low spontaneous polarization and improved crystal quality as strain-related effects are eliminated. Both concepts for e-mode HEMTs are presented and compared in terms of electrical performance and structural properties.