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
you have a frequency dependence of the accumulation capacitance, which is due to the dielectric layer.
The frequency dispersion can be due to two different reasons, extrinsic, or intrinsic.
Extrinsic effects give rise to strong frequency dispersion due to contact effects, inter diffusion effect with neighbouring materials which can be aggravated by any high temperature processing during the layer growth.
Intrinsic effects due to changes in the bulk conductance of the dielectric layer, and could be due to the combined effects grains, grain boundaries, in case the dielectric is a poly-crystalline layer.
K. Sreenivas
Dear Prof A. Sreenivas,
thank you for your answer. If this effect is due to the dielectric layer, then why it is so important in the Al2O3/GaN stack compared to the Al2O3/Si stack ?
M.A.Mahjoub
hello
this effect is related to series resistance only. you can see my article
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