Adjustment of threshold voltage in AlN/AlGaN/GaN high-electron mobility transistors by plasma oxidation and Al2O3 atomic layer deposition overgrowth

• Published in: Applied physics letters Vol. 104; no. 1
• Main Authors: Gregušová, D., Jurkovič, M., Haščík, Š., Blaho, M., Seifertová, A., Fedor, J., Ťapajna, M., Fröhlich, K., Vogrinčič, P., Liday, J., Derluyn, J., Germain, M., Kuzmik, J.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 06-01-2014
• Subjects: Aluminum gallium nitrides; Aluminum nitride; Aluminum oxide; Applied physics; Atomic layer epitaxy; Density; Gallium nitrides; High electron mobility transistors; Oxidation; Semiconductor devices; Threshold voltage; Transistors
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4861463

We discuss possibilities of adjustment of a threshold voltage VT in normally off GaN high-electron mobility transistors (HEMTs) without compromising a maximal drain current IDSmax. Techniques of a low power plasma or thermal oxidation of 2-nm thick AlN cap over 3-nm thick AlGaN barrier are developed and calibrated for a thorough oxidation of the cap with a minimal density of surface donors at the inherent oxide-semiconductor interface. It has been shown that while a thermal oxidation technique leads to the channel and/or interface degradation, low density of surface donors and scalability of VT with additionally overgrown Al2O3 may be obtained for plasma oxidized HEMTs. With 10-nm thick Al2O3 deposited at 100 °C by atomic-layer deposition, we obtained VT of 1.6 V and IDSmax of 0.48 A/mm at a gate voltage of VGS = 8 V. Density of surface donors was estimated to be about 1.2 × 1013 cm−2, leaving most of the negative polarization charge at the semiconductor surface uncompensated. Further reduction of surface donors may be needed for even higher VT.