Electrical and material properties of plasma‐enhanced atomic layer deposited (PE‐ALD) AlON on dry‐etched n‐type GaN substrates are investigated for nitrogen concentration ranging from 1.5% to 7.1%. Firstly, an increase in flat‐band voltage (V_FB) and its hysteresis with increasing nitrogen concentration is reported. The increase in V_FB is associated with the nitrogen content whereas the increase in hysteresis to the presence of impurities (hydroxyl groups and carbon‐related impurities). Alongside the nitrogen concentration, the impact of different post‐deposition annealing (PDA) temperatures is studied (400–800 °C). Stable AlON layers and interfaces with etched GaN substrates are reported with slight gallium oxide growth or gallium diffusion towards the dielectric layer. Finally, with increasing PDA temperature, an increase in V_FB and a significant reduction of both V_FB hysteresis and interface state density (D_it) are observed, notably at the measuring temperature of 150 °C. These results present a promising pathway toward more reliable and stable normally‐OFF GaN‐based MOS‐channel high electron mobility transistors (MOSc‐HEMTs).

Homogeneous AlOxNy thin films with a controlled nitrogen composition, up to 7.1%, were grown on GaN substrate using plasma-enhanced atomic layer deposition. This was achieved through repeated cycles consisting of AlN thin layers deposition and subsequent in situ O2 plasma oxidation under optimized conditions. We demonstrate that the nitrogen concentration in AlOxNy films can be finely tuned from 1.5% to 7.1% by a precise control of the AlN thin film thickness from 0.25 to 0.96 nm before each oxidation step. It is shown also that higher AlN thickness, ≥1.96 nm, leads to an incomplete plasma oxidation of AlN films, resulting in the formation of AlOxNy/AlN-like structures. Several structural and physic-chemical characterizations, including focused ion beam-scanning transmission electron microscopy, Auger electron spectroscopy, XPS, and time-of-flight secondary ion mass spectrometry were performed to confirm these findings. These results highlight the importance of this approach for growing homogeneous AlOxNy thin films with controlled nitrogen doping, which can be used as dielectrics in gate stacks for high performance GaN-based transistors.

In this article, we demonstrate that the combination of ToF-SIMS, magnetic SIMS (M-SIMS), and high-energy x-ray photoelectron spectroscopy (HAXPES) is a powerful, comprehensive approach to study the quality of buried interfaces in III–V-based heterostructures. This multitechnique method enables us to track rigorously possible interdiffusion of key elements (In, Ga, As, Al, P) and dopants. Sharp interfaces were observed from ToF-SIMS profiles acquired with an upward depth resolution as low as 1.5 nm using a Cs+ sputtering source. For the detection of Zn doping in the layers, M-SIMS was preferred to ToF-SIMS thanks to its superior sensitivity. HAXPES was finally found to be a very complementary technique to check the abruptness of the top InGaAs/InP buried interface, taking benefit of its deeper probing ability when compared to the usual lab XPS. Our results confirm the high quality of the heterostructure with abrupt interfaces, no interdiffusion, and good control of the doping with an effective InAlAs spacer blocking Zn diffusion in InP.