HC Verma Chapter 45 Problem 8

Problem Statement

What is barrier potential of a p-n junction and why does it form?

Key Concepts

Contact potential, depletion layer, diffusion

Relevant Formulas

eV0 = kT*ln(NA*ND/ni^2)

Step-by-Step Solution

Diffusion of electrons to p-side and holes to n-side creates fixed ion space charge, building an electric field. Equilibrium when drift = diffusion currents. eV0 = kT*ln(NA*ND/ni^2). Si: V0 = 0.6-0.7 V; Ge: 0.2-0.3 V.

Final Answer

V0 = 0.6-0.7 V (Si); 0.2-0.3 V (Ge)

Tips and Tricks

Barrier blocks majority carriers; minority carriers cross freely.

Common Mistakes

Always use SI units. Check energy conservation accounts for all forms.