Systematic analysis of the trapping and reliability of Al2O3/GaN MOS capacitors with different atomic layer deposition techniques

We investigate the robustness and charge trapping phenomena under positive and negative bias stress in Al2O3/n-GaN metal-oxide-semiconductor capacitors fabricated with different atomic layer deposition (ALD) techniques: (i) thermal ALD (ThALD), (ii) plasma-enhanced ALD (PEALD), and (iii) stacked-ALD, obtained by alternating the latter two. The results, obtained by means of standard I-V and pulsed-CV measurements, show that PEALD results in the best oxide robustness under positive voltage stress, while ThALD results in the lowest charge trapping. We demonstrate that stacked-ALD layers presents the best trade-off to maximize robustness and minimize charge trapping phenomena, clearing the way for application in GaN MOSFET fabrication. Additionally, we compare the performance of different in-situ plasma pre-treatments on the GaN surface, proving that the NH3 plasma is effective for improving the device performance in terms of trapped charge and reliability. The results confirm the beneficial role of stacked ALD deposition and surface pre-treatments on the electrical stability and reliability of oxide layers.