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Common Data for Questions 71,72,73:
The figure shows the high-frequency capacitance-voltage (C-V) characteristics of a $\mathrm{Metal} / \mathrm{SiO}_{2} / \text{silicon (MOS)}$ capacitor having an area of $1 \times 10^{-4} \mathrm{~cm}^{2}$. Assume that the permittivities $\left(\varepsilon_{0} \varepsilon_{r}\right)$ of silicon and $\mathrm{SiO}_{2}$ are $1 \times 10^{-12} \mathrm{~F/cm}$ and $3.5 \times 10^{-13} \mathrm{~F/cm}$ respectively.

Consider the following statements about the $\mathrm{C}-\mathrm{V}$ characteristics plot:

$\text{S1:}$ The MOS capacitor has an $n$-type substrate.
$\text{S2:}$ If positive charges are introduced in the oxide, the $\mathrm{C}-\mathrm{V}$ plot will shift to the left.

Then which of the following is true?

1. Both $\mathrm{S} 1$ and $\mathrm{S} 2$ are true
2. $\mathrm{S} 1$ is true and $\mathrm{S} 2$ is false
3. $\mathrm{S} 1$ is false and $\mathrm{S} 2$ is true
4. Both $\text{S1}$ and $\text{S2}$ are false