(Invited, Digital Presentation) High-κ Gate Oxide Integration and Ohmic Contact Development for AlGaN/GaN MISHEMTs

Abstract

GaN based devices are one of the main candidates for current power electronics and RF applications [1,2]. For optimizing device performance, a detailed understanding of the defects contained in the material and the passivation capability of dielectric layers, i.e., the interfacial defect states formed, is mandatory. Here, we will focus on the surface defect passivation and gate leakage current reduction by introducing thin dielectric films as gate insulator in a so-called MISHEMT (metal insulator semiconductor high electron mobility transistors) device using different materials. The impact of a fully amorphous dielectric (Al2O3), which was kept amorphous by the integration of a low thermal budget ohmic contact [3], was compared to an epitaxial dielectric film (GdScO3) [4]. Due to the band alignment and the high dielectric constant of GdScO3, the spillover effect as it was seen for Al2O3 [5] has been suppressed and a reduction of threshold voltage shift due to the additional capacitance by the dielectric layer has been achieved. In addition, AlTiOx films were investigated as gate dielectrics [6]. To avoid further deterioration of the dielectric layer by the ohmic contact formation anneal, a gate last integration scheme was carried out using Ti based gold free ohmic source and drain contacts [7]. By varying the Al content, the band alignment between the underlying GaN capping layer to the thin film dielectric was controlled. By this means and additional charge engineering in the dielectric layer, a gate leakage reduction with limited threshold voltage increase has been realized. All dielectric layers have been electrically characterized in detail. Interface trap densities were measured by photo-assisted capacitance voltage measurements and an in-depth comparison of the dielectric layers and their impact on the device performance will be given.[1] Yole Developpement, RF GaN Market: Applications, Players, Technology and Substrates 2019, Market & Technology Report, (2019)[2] T. Kimoto, Jpn. J. Appl. Phys. 54, 40103 (2015).[3] Schmid, A.; Schröter, Ch.; Otto, R.; Schuster, M.; Klemm, V.; Rafaja, D.; Heitmann, J., Appl. Phys. Lett. 106, 053509 (2015)[4] Seidel, S., Schmid, A., Miersch, C., Schubert, J., Heitmann, J. Appl. Phys. Lett., 118(5), 052902 (2021)[5] P. Lagger, P. Steinschifter, M. Reiner, M. Stadtmüller, G. Denifl, A. Naumann, J. Müller, L. Wilde, J. Sundqvist, D. Pogany, C. Ostermaier, Appl. Phys. Lett. 105, 033412 (2014)[6] N Siebdrath, S. Seidel, A. Schmid, J. Heitmann, Mikro-Nano-Integration; 8th GMM-Workshop, 2020, pp. 1-3.[7] Garbe, V.; Schmid, A.; Seidel, S.; Abendroth, B; Stöcker, H.; Doering P.; Meyer, D.C.; Heitmann, J., Phys. Stat. Sol. (B), 2100312 (2021)