Question

The charge carriers move gradually from the region of high carrier density to low carrier density constitutes an electric current is

• A. Drift current
• B. Diffusion current
• C. Leakage current
• D. Current density

Hint:

\[ \text{Electric Field} \Rightarrow \text{Drift Current} \] \[ \text{Concentration Gradient} \Rightarrow \text{Diffusion Current} \] These two currents are fundamental in semiconductor devices.

Answer 1

The Correct Option is B

Concept: In semiconductors, charge carriers can move due to two primary mechanisms:
• Drift due to an applied electric field.
• Diffusion due to concentration gradient. When carriers move from a region of higher concentration to a region of lower concentration, a diffusion current is produced.

Step 1: Understand carrier concentration gradient.
Suppose a semiconductor has a large concentration of electrons in one region and a smaller concentration in another region. Due to random thermal motion, electrons naturally move from the region of high concentration toward the region of low concentration. \[ \text{High Concentration} \longrightarrow \text{Low Concentration} \]

Step 2: Identify the resulting current.
The current produced due to the movement of carriers under the influence of concentration difference is known as diffusion current. No external electric field is required for this phenomenon.

Step 3: Differentiate from drift current.
Drift current occurs because of an applied electric field. Diffusion current occurs because of a concentration gradient. Since the question refers to carrier movement from high density to low density, \[ \boxed{\text{Diffusion Current}} \] is the correct answer.