Suppose a ‘n’-type wafer is created by doping Si crystal having 5 × 10²⁸ atoms/m³ with 1ppm concentration of As. On the surface 200 ppm Boron is added to create ‘P’ region in this wafer. Considering n_i = 1.5 × 10¹⁶ m^–3, (i) Calculate the densities of the charge carriers in the n & p regions. (ii) Comment which charge carriers would contribute largely for the reverse saturation current when diode is reverse biased.

Question

Philoid · Accepted Answer

i) Each arsenic atom will provide on electron. Hence, density of electrons will be

We also know that

So density of holes in this side will be,

When boron is added to the other side then each atom will contribute to one hole. So, density of holes will be,

Now the concentration of electrons will be,

ii) Density of holes in n region is

Density of electron in p region is

So, holes in n region will contribute more to the reverse saturation current.