Marie-Antoinette di Forte-Poisson

Dual-purpose BGaN layers on performance of nitride-based high electron mobility transistors

A GaN/ultrathin BGaN/GaN heterojunction is used in AlGaN/GaN high electron mobility transistors (HEMTs) to provide an electrostatic barrier to electrons and to improve the confinement of the 2-dimensional electron gas. BGaN back-barrier layers limit leakage in the GaN buffer thanks to two effects: a polarization-induced band discontinuity and a resistive barrier originating from excellent insulation properties of BGaN. Compared to conventional AlGaN/GaN HEMTs, structures grown with BGaN back-barrier showed a significant improvement of static performances, transport properties, and trapping effects involving a limited current collapse in dynamic regime. A DC maximum current increase of 58.7% was observed.

High electron mobility in high-polarization sub-10 nm barrier thickness InAlGaN/GaN heterostructure

We report on the improvement of the electron transport properties of the two-dimensional electron gas (2DEG) confined at a nearly lattice-matched quaternary barrier InAlGaN/AlN/GaN heterostructure using a sub-10 nm ultrathin barrier. Electron mobilities of 1800 (RT) and 6800 cm2 V−1 s−1 (77 K) are achieved while delivering a high electron density of 1.9 × 1013 cm−2, resulting in extremely low sheet resistances of 191 Ω/ at RT and below 50 Ω/ at 77 K. These 2DEG properties exceed the best ones ever reported for III–N structures. The excellent current and power gain cut-off frequencies of 60 and 190 GHz at VDS = 15 V obtained using 0.25 µm technology reflect the outstanding 2DEG properties.

Highlighting trapping phenomena in microwave GaN HEMTs by low-frequency S -parameters

This paper presents an original characterization method of trapping phenomena in gallium nitride high electron mobility transistors (GaN HEMTs). This method is based on the frequency dispersion of the output-admittance that is characterized by low-frequency S-parameter measurements. As microwave performances of GaN HEMTs are significantly affected by trapping effects, trap characterization is essential for this power technology. The proposed measurement setup and the trap characterization method allow us to determine the activation energy Ea and the capture cross-section σn of the identified traps. Three original characterizations are presented here to investigate the particular effects of bias, ageing, and light, respectively. These measurements are illustrated through different technologies such as AlGaN/GaN and InAlN/GaN HEMTs with non-intentionally doped or carbon doped GaN buffer layers. The extracted trap signatures are intended to provide an efficient feedback to the technology developments

Degradation of dc and pulsed characteristics of InAlN/GaN HEMTs under different proton fluences

Displacement-damage induced degradation in InAlN/GaN structures is studied for different proton fluences, from 110¹⁴ p/cm² to 410¹⁴ p/cm², at 3MeV. DC analysis reveals that devices experience a V_TH positive shift and an increase of the R_ON, following a linear trend with the proton radiation fluence, as a consequence of the creation of acceptor-like traps. Furthermore an increase of the diode gate current is noticed. Pulsed measurements indicate an increase of the so called “current collapse”, especially when a high gate drain voltage difference is applied, as a consequence of the performances variation in the dynamic max g_m, V_TH shift and R_ON.

Deuterium Out-Diffusion Kinetics in Magnesium-Doped GaN

A series of isothermal annealing experiments have been performed in the range 790–920°C under N 2 flow in order to study the deuterium out-diffusion kinetics of Mg-doped GaN grown on sapphire under deuterated ammonia. The deuterium concentration was measured by SIMS analysis before and after each annealing step. The kinetics closely follow a first-order law. The activation energy related to the deuterium out-diffusion process is 3.1 eV. In addition, deuterium effusion measurements were performed measuring the molecular HD flux while the specimens were annealed in ultra high vacuum with a linear heating rate. In contrast to SIMS, this method detects the species that migrated out of the sample. Effusion peaks of the HD flux at 360 and 490°C are attributed to the fragmentation of adsorbed CH x D y complexes. The molecular HD flux starts increasing at 800°C which is the onset of the GaN decomposition and has its maximum at 920°C. This HD flux is accompanied by the desorption of H and D containing radicals and molecules desorbing above 900°C.