Question

A Si and a Ge diode has identical physical dimensions. The band gap in Si is larger than that in Ge. On applying identical reverse bias across these diodes,

• A. The reverse current in Ge is lesser than that in Si.
• B. The relative magnitudes of reverse currents cannot be determined from the given data.
• C. The reverse current is identical in both cases.
• D. The reverse current in Ge is larger than that in Si.

Hint:

Germanium diodes have higher reverse saturation current than silicon because Ge has smaller band gap.

Answer 1

The Correct Option is D

Step 1: Understand reverse current in diode.
Reverse current in a diode is mainly due to minority charge carriers. This current is called reverse saturation current.

Step 2: Dependence on band gap.
Reverse saturation current depends strongly on the band gap of the semiconductor.
\[ I_s \propto e^{-\frac{E_g}{kT}} \]

Step 3: Compare band gaps of Si and Ge.
Silicon has a larger band gap than germanium.
\[ E_{g(\text{Si})}>E_{g(\text{Ge})} \]

Step 4: Effect on reverse current.
Since reverse current is inversely related to band gap (exponentially), smaller band gap means larger reverse current.
Thus, germanium will have more reverse current than silicon.

Step 5: Effect of identical dimensions and bias.
Since both diodes have same dimensions and same reverse bias, the difference arises only due to material property (band gap).

Step 6: Final conclusion.
\[ \boxed{\text{Reverse current in Ge is greater than in Si}} \] Hence, correct answer is option (D).