The effects of N2 and O2:N2 (1:1) as ambient gases during activation annealing of Mg as p-type doping of GaN have been investigated. The purpose was to understand the mechanisms involved and especially the impact of O2 on the resulting hole concentration and hole mobility. The addition of O2 to the ambient gas during annealing is known to be very effective in reducing the H level of the Mg-doped GaN layer, but the maximum achievable hole concentration and mobility, as determined by Hall characterization, is still higher with pure N2. The difference is explained by an in-diffusion of O to the GaN layer acting as n-dopant and thus giving rise to a compensation effect. It is found that to a large degree only the Mg-H complexes at substitutional (MgGa), i.e., the electrically active acceptor sites that provide free holes, are activated by annealing with N2 only as ambient gas, while annealing with O2:N2 (1:1) also dissociates electrically inactive Mg-H complexes resulting in much less residual H. Thus, the residual H level in relation to the Mg level after activation annealing with N2 only may provide a representative measure of the resulting free hole concentration of the Mg-doped GaN layer.

We present a systematic investigation of activation annealing of Mg as p-type doping in GaN. The diffusion of Mg and H by rapid thermal processing (RTP) at 700 °C to 975 °C together with the effect of the ambient gas are investigated by SIMS, XRD, AFM, and electrical measurements. The observed diffusion of H to the substrate emphasizes the importance of understanding the diffusion and reactions of ambient N, O, and H in the GaN layers.We conclude that optimization of the resulting hole density, except the Mg concentration and RTP temperature, the surface morphology, the thickness of the Mg-doped GaN and the thickness of any layer covering it must be considered. 

Here, we investigate the effects of O2:N2 (1:1) as ambient gas as compared with pure N2 during activation annealing of Mg as p-type doping in GaN layers grown by MOCVD. The purpose is to understand the impact of O2 on the resulting free hole concentration and hole mobility using SIMS, XRD, STEM, AFM, and Hall effect measurements. Even though the presence of O2 in the ambient gas during annealing is very effective in reducing the H level of the Mg-doped GaN layers, the maximum achievable hole concentration and mobility is still higher with pure N2. The differences are explained by an in-diffusion of O to the GaN layer acting as n-dopant and, thus, giving rise to a compensation effect. The Mg-H complexes at substitutional (MgGa), i.e., the electrically active acceptor sites that provide free holes, are preferentially activated by annealing with N2 only as ambient gas, while annealing with O2:N2 (1:1) also dissociates electrically inactive Mg-H complexes resulting in much less residual H. At the lower growth pressure of 150 mbar compared to higher growth pressure of 300 mbar, an increasing carbon incorporation leads to a compensation effect drastically reducing the free hole concentration while the mobility is unaffected. © 2023 Author(s).

This paper reviews recent progress and key challenges in process and reliability for high-performance vertical GaN transistors and diodes, focusing on the 200 mm CMOS-compatible technology. We particularly demonstrated the potential of using 200 mm diameter CTE matched substrates for vertical power transistors, and gate module optimizations for device robustness. An alternative technology path based on coalescence epitaxy of GaN-on-Silicon is also introduced, which could enable thick drift layers of very low dislocation density. © 2021