Question

Arrange the following semiconductors in descending order of band gap :
A. Si
B. Ge
C. GaP
D. ZnS
E. SiC

• A. \(D > E > C > A > B \)
• B. \(E > D > C > B > A \)
• C. \(D > E > A > C > B \)
• D. \(A > B > C > D > E \)

Hint:

Band gap generally increases as you move up a group in the periodic table (smaller atoms) or as the ionicity of the bond increases (e.g., II-VI compounds like ZnS usually have larger gaps than IV elements like Si).

Answer 1

The Correct Option is A

Concept: The energy band gap ($E_g$) is the energy difference between the top of the valence band and the bottom of the conduction band. Materials with larger band gaps are typically more insulating, while smaller band gaps are found in more conductive semiconductors.

Step 1: Determine the approximate band gap values for each material.

• D. ZnS (Zinc Sulfide): Wide band gap semiconductor, $E_g \approx 3.6 \text{ eV}$.
• E. SiC (Silicon Carbide): Wide band gap, $E_g \approx 2.3 \text{ to } 3.3 \text{ eV}$ (depending on the polytype, e.g., 6H-SiC is $\sim 3.0 \text{ eV}$).
• C. GaP (Gallium Phosphide): $E_g \approx 2.26 \text{ eV}$.
• A. Si (Silicon): Standard semiconductor, $E_g \approx 1.1 \text{ eV}$.
• B. Ge (Germanium): Small band gap semiconductor, $E_g \approx 0.67 \text{ eV}$.

Step 2: Arrange in descending order.
Order: ZnS ($3.6$) > SiC ($3.0$) > GaP ($2.26$) > Si ($1.1$) > Ge ($0.67$). This corresponds to: \(D > E > C > A > B\).