In the case of AL2O3/GaN stack a serious frequency dispersion is observed (Fig1) whereas this problem is negligible in the Al2O3/Si case (Fig.2). Moreover, the increase of the capacitance area exacerbating this problem in the AL2O3/GaN case and is still acceptable in the Al2O3/Si case. It is to note that the two stacks were done in the same conditions. Before the ALD deposition of the 10 nm of Al2O3 at 250° the Si and GaN surfaces were immersed into 5% HF for 1 min.

Then, I want to know the cause of this problem and how to solve it.

Yours sincerely

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