Year: 2017

Ir/Al multilayer Gates for High Temperature Operated AlGaN/GaN HEMTs

Ir/Al multilayer Gates for High Temperature Operated AlGaN/GaN HEMTs

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Lalinský, T., Vanko, G., Dobročka, E., Osvald, J., Babchenko, O., Dzuba, J., Veselý, M., Vančo, L., Vogrinčič, P., Vincze, A.

Physica Status Solidi (A) Applications and Materials Science, Volume 214, Issue 12, December 2017, Article number 1700691
DOI: 10.1002/pssa.201700691

Abstract

The fabrication and characterization of the sequentially evaporated Ir/Al multilayer gates of AlGaN/GaN circular high electron mobility transistors formed by high temperature oxidation is reported. Annealing at temperature of 800 °C, for 60 s in O2 ambient makes possible to form a sharp gate interface with a high Schottky barrier height at RT (φb = 1.2 eV). It is also shown that high temperature oxidation can be an effective approach in reducing of both the gate and drain leakage currents of high electron mobility transistors (more than six orders). A comprehensive microstructural, electrical, and electro‐thermal characterization of the Ir/Al gates is carried out to study the thermal stability of the gate interface and high temperature performance of the devices. Stable operation of the devices with multilayer Ir/Al gates in the temperature range up to 500 °C is demonstrated. Here, it is proposed that the thermal stability of the interface is controlled by the formed aluminum oxide interfacial layer. Finally, perfectly clear pinch‐off characteristics and thermally induced threshold voltage (Vth) instability as low as −0.58 mV °C−1 are achieved.

Thermally induced age hardening in tough Ta-Al-N coatings via spinodal decomposition

Thermally induced age hardening in tough Ta-Al-N coatings via spinodal decomposition

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Mikula, M., Sangiovanni, D.G., Plašienka, D., Roch, T., Čaplovičová, M., Truchlý, M., Satrapinskyy, L., Bystrický, R., Tonhauzerová, D., Vlčková, D., Kúš, P.

Journal of Applied Physics 121, 2017, 155304

doi.org/10.1063/1.4981534

Abstract

We combine experiments and ab initio density functional theory calculations to investigate the evolution in structural and mechanical properties of TaAlN coatings as a function of the annealing temperature T. Formation of coherent cubic TaN- and AlN-rich nanometer-size domains, occurring during the initial stage of thermally induced phase separation within cubic NaCl-type (B1) TaAlN solid solutions, yields a monotonic increase in hardness from 29 GPa (as deposited coatings) up to a maximum of 35 GPa (+17%) reached after annealing at 1000 °C. Further thermal treatment at T > 1000 °C leads to the transformation of metastable cubic domains into stable hexagonal TaNx and wurtzite AlN phases, thus resulting in hardness reductions. A comparison of our results with those reported in the literature reveals that TaAlN coatings are at least as hard while considerably less stiff (lower elastic moduli) than TiAlN coatings, thus indicating a substantial increase in toughness achieved upon replacing Ti with Ta in the host lattice. Present findings suggest that cubic TaAlN solid solutions are promising candidates for applications in protective coatings possessing both high-temperature hardness and toughness. © 2017 Author(s).

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Influence of GaN/AlGaN/GaN (0001) and Si (100) substrates on structural properties of extremely thin MoS2 films grown by pulsed laser deposition

Influence of GaN/AlGaN/GaN (0001) and Si (100) substrates on structural properties of extremely thin MoS2 films grown by pulsed laser deposition

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Š. Chromik, M. Sojková, V. Vretenár, A. Rosová, E. Dobročka, M. Hulman

doi.org/10.1016/j.apsusc.2016.06.038

Abstract

Very thin MoS2 films were prepared on hexagonal GaN/AlGaN/GaN (0001) and Si (100) substrates from a stoichiometric target by a pulsed laser deposition. Combined results from Raman and X-ray reflectivity measurements have shown that the thinnest samples are 2–2.5nm thick. The thickness increases with the number of laser pulses applied albeit no simple direct proportion between the two quantities has been observed. Concerning the stoichiometry, the distribution of Mo and S elements within as-deposited films is rather complex. The stoichiometric MoS2 is making-up only a part of the film. In spite of this, selected area electron diffraction studies have clearly confirmed that the films deposited on Si (100) are nanocrystalline and oriented perpendicularly to the substrate surface while an epitaxial growth of MoS2 films was observed on GaN/AlGaN/GaN (0001) substrates.