Appeared in: 2025 (3 sets)
Draw energy band diagrams of n-type and p-type semiconductors at temperature $T > 0\text{ K}$. Show the donor/acceptor energy levels with the order of difference of their energies from the bands.
✓ Verified CBSE Marking Scheme
Official Evaluation Steps
Step 1 (Conceptual Definition):
At temperature $T > 0\text{ K}$, thermal excitation causes electrons to move from the valence band to the conduction band. In doped semiconductors, additional energy levels are introduced within the forbidden energy gap:
- n-type: A donor energy level ($E_D$) is created just below the conduction band ($E_C$).
- p-type: An acceptor energy level ($E_A$) is created just above the valence band ($E_V$).
(1 Mark for correct identification and placement of levels)
Step 2 (Energy Band Diagrams):
The diagrams must clearly show the forbidden energy gap ($E_g$) and the relative positions of $E_D$ and $E_A$.
n-type Semiconductor
p-type Semiconductor
(0.5 Mark for correct diagrammatic representation)
Step 3 (Energy Difference Specification):
The energy difference between the impurity levels and the respective bands is very small, typically of the order of $0.01\text{ eV}$ for Germanium and $0.05\text{ eV