This paper proposes a new technique to engineer the Fin channel in vertical GaN FinFET toward a straight and smooth channel sidewall. Consequently, the GaN wet etching in the TMAH solution is detailed; we found that the m-GaN plane has lower surface roughness than crystallographic planes with other orientations, including the a-GaN plane. The grooves and slope (Cuboids) at the channel base are also investigated. The agitation does not assist in Cuboid removal or crystallographic planes etching rate enhancement. Finally, the impact of UV light on m and a-GaN crystal plane etching rates in TMAH has been studied with and without UV light. Accordingly, it is found that the m-GaN plane etching rate is enhanced from 0.69 to 1.09 nm/min with UV light; in the case of a-GaN plane etching, UV light enhances the etching rate from 2.94 to 4.69 nm/min.

During the fabrication of metal oxide semiconductor high electron mobility transistor based on AlGaN/GaN heterostructure, gate patterning is recognized as the most critical step that can lead to electrical degradation of the transistor. In this work, we performed the SiN cap layer plasma etching processes by two fluorine-based plasma processes (SF6/Ar and CHF3/CF4/Ar) with low (≈15 eV) and high (≈260 eV) ion energies. Moreover, we investigate the postetching treatment using a KOH solution in order to restore the quality of the AlGaN barrier surface after etching. The objective of this article is to evaluate the AlGaN barrier surface damage after the listed plasma etching processes and postetching strategies by using quasi-in situ angle-resolved x-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscope. Accordingly, it is found that both high ion energy plasma processes lead to a significant stoichiometric change and modification of the AlGaN barrier layer into a 1.5 nm F-rich AlGaNFx subsurface reactive layer. The decrease in ionic energy leads to a decrease in the SiN etch rate and a significant improvement in the SiN/AlGaN etch selectivity (which becomes infinite) for both plasma chemistries. Moreover, the decrease in ion energy decreases the depth of the modification (about 0.5 nm) and reduces the stochiometric change of the AlGaN barrier layer. However, both low and high ion energy SF6/Ar plasma lead to 0.8 eV Fermi level shift toward the valence band. Furthermore, the KOH postetching treatment demonstrates complete and effective removal of the AlGaNFx subsurface reactive layer and restoration of the surface properties of the AlGaN layer. However, this removal leads to AlGaN recesses that are correlated to the thickness of the reactive layer formed during the etching.

Rectifying Titanium Nitride (TiN) gate contact technology is developed for AlGaN/GaN based micro and nanometer HEMTs. A high compressive strain occurring in thinner TiN films (ranging from 5 nm to 60 nm), deposited by sputtering, leads to a reduction in tensile strain at the surface of AlGaN barrier. The diminution in tensile strain forms a pseudo-p-type layer (diode-like). This strain reduction has no effect on the bandgap of the AlGaN barrier layer, allowing the gate to withstand a reverse gate bias larger than 100 V. Characterization using the high-resolution transmission electron microscopy combined with the X-ray photoelectron spectroscopy reveals a good TiN/AlGaN interface quality and no diffusion of TiN into AlGaN. The effective energy barrier of the rectifying nanoscale TiN gate contact has a relatively large height of 1.1 eV associated with an ideality factor of 1.4. A dramatic drop of the reverse-bias leakage current down to 11 pA/mm is measured at -30 V. In addition, electrical measurements show very low gate and drain lag effects of 4.2 % and 6.7 %, respectively.

This paper reports on the thermal impedance measurement of GaN high‐electron‐mobility‐transistors (HEMTs) using frequency‐resolved gate resistance thermometry. Corrections methods are used to enable measurement on a very broad frequency range up to the MHz range. Transposition to time‐domain is then conducted and allows, for the first time to the author's knowledge, a full determination of the device's thermal impedance with a time‐resolution down to 60 ns and no limitation on the maximum time range with a single measurement technique. Measurements are performed for HEMTs with different gate‐lengths and compared with literature. The experimental results demonstrate the validity and interest of the technique for the thermal impedance extraction of GaN based devices.

The impact of Cubic Silicon Carbide (3C-SiC) transition layer on breakdown voltage and frequency performance of GaN high electron mobility transistors is investigated. A combination of distinct material and device characterizations techniques, including Raman spectroscopy, coplanar waveguides, electrical measurements, and Technology Computer-Aided Design (TCAD) simulations, are adopted to inspect the role of the 3C-SiC interlayer. Raman spectra reveal a good quality of the 3C-SiC layer, similar to the mono-crystalline 3C-SiC spectra. A relatively low transmission loss of ∼0.16 dB/mm at 40 GHz is measured for the device with 3C-SiC layer, rather than 2.1 dB/mm for the device without 3C-SiC. In addition, a soft breakdown voltage around 1530 V at 1 μA/mm is achieved, which is three times larger compared with that of the conventional device. The failure mechanism, related to carrier injection at the nucleation layer, is not observed in the structure with the 3C-SiC layer. Instead, TCAD simulations disclose a substantial improvement of the buffer/substrate interface through the suppression of an interface current path.