THE ELECTRICAL IMPEDANCE OF A METAL-SILICON STRUCTURE WITH A THIN SiO2 LAYER

Dmytro Slobodzyan, Markiyan Kushlyk, Yaroslav Shpotyuk, Roman Lys, Andriy Luchechko

Abstract


Background. Silicon-based Metal-Oxide-Semiconductor (MOS) structures with an SiO2 dielectric layer are widely used in various modern electronic devices. Therefore, investigating the electrical properties of such structures remains a relevant task. Impedance spectroscopy is particularly valuable for studying these properties, as it enables the examination of charge transport mechanisms, interfacial properties, and the determination of parameters for equivalent electrical circuits.

Materials and Methods. Samples of n-type monocrystalline silicon were investigated, featuring the following characteristics: doping impurity – arsenic, resistivity – ρ = 0.003 Ohm·cm, thickness – 0.5 mm, area – 30 mm2. A metal-semiconductor-metal type structure (Ag-SiO2-Si-SiO2-Ag) was formed on the surface of such a sample.

To study the frequency dependencies of the impedance of the formed structure, a setup based on the HIOKI IM3536 RLC meter was used.

Results and Discussion. The frequency dependencies of the real and imaginary components of the impedance of the Ag-SiO2-Si-SiO2-Ag structure were investigated in the frequency range from 4 Hz to 8 MHz at different excitation electric field amplitudes. It was established that for all values of the excitation signal amplitude, the real component of the impedance, Re(Z), decreases as the frequency and AC excitation amplitude increase. The frequency dependencies of the imaginary component of the impedance, Im(Z), demonstrate the presence of relaxation maxima. With an increase in the excitation signal amplitude, the amplitude of these maxima decreases significantly. The observed changes in the impedance of such a structure can be explained based on its multilayer nature and the properties of highly-doped silicon and the thin layers of native silicon oxide.

Conclusion. The impedance spectroscopy study of Ag-SiO2-Si-SiO2-Ag structures with native oxide layers revealed a strong non-linear dependence of electrical properties on the AC signal amplitude. The results demonstrate that in MOS structures with ultra-thin oxides, the “insulating” layer acts as a field-dependent tunneling resistor. Impedance spectroscopy proves to be an effective method for distinguishing between capacitive accumulation and tunneling leakage regimes in such highly doped semiconductor systems.

Keywords: silicon, impedance spectroscopy, MOS structure, Nyquist plot.


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References


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DOI: http://dx.doi.org/10.30970/eli.32.12

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