WEEK 1 TASK 1, identify the type of substrate.

The substrate is p-type Si. 

When V<0, the left part of the curve is nearly flat, which shows that it is accumulation region. When a negative voltage is applied between the metal gate and the semiconductor, it causes an equal net positive charge to accumulate at the interface between the semiconductor and the oxide. The holes appear in the valence band at the oxide-semiconductor interface when it is p-type.

In the ideal MOS Curves

In the accumulation region (V < 0), no depletion region, accumulation 

of holes at semiconductor surface. 

In the depletion region (0 < V < VT),  the total capacitance is a series combination of Co and , so that . 

C decreases as V increases, given by

In the inversion region (V > VT), the depletion region reaches the 

maximum Wm, and, total capacitance is given by 

Reference

S. M. Sze and M. K. Lee, Semiconductor Devices: Physics and Technology, 3rd Edition, Wiley, Hoboken (2013) chapter 5, page 167