Question:easy
Consider carrier transport in a Zener diode in the breakdown region. Which is the dominant transport mechanism for current flow in this case?
Consider carrier transport in a Zener diode in the breakdown region. Which is the dominant transport mechanism for current flow in this case?
Show Hint
A Zener diode is doped heavily on both sides, giving a thin depletion region where carriers can cross the barrier directly under a high field.
Updated On: Jul 20, 2026
- Drift
- Diffusion
- Tunneling
- Ballistic transport
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Separate the two breakdown mechanisms in reverse-biased diodes.
A reverse-biased p-n junction can break down in two distinct ways: Zener breakdown and avalanche breakdown. Knowing the difference settles the answer here.
Step 2: Describe avalanche breakdown first, as a contrast.
In lightly doped diodes with a wide depletion region, carriers accelerated by the field pick up enough kinetic energy through drift to knock other electrons loose in collisions, building current through impact ionization. This needs a wide region for the carriers to gain speed in.
Step 3: Describe Zener breakdown, which applies here.
A Zener diode is doped heavily on purpose, so its depletion region is very narrow. In such a narrow region a carrier cannot pick up much energy from drift before crossing it. Instead, the field is strong enough that electrons pass straight through the thin barrier by tunneling, a purely quantum effect that does not need the carrier to gain kinetic energy first.
Step 4: Match this to the question.
Since the question names it a Zener diode and asks specifically about its breakdown region, the dominant mechanism is this tunneling process, not drift-driven avalanche multiplication, and not diffusion or ballistic transport, neither of which describes junction breakdown at all.
\[ \boxed{\text{Tunneling}} \]
A reverse-biased p-n junction can break down in two distinct ways: Zener breakdown and avalanche breakdown. Knowing the difference settles the answer here.
Step 2: Describe avalanche breakdown first, as a contrast.
In lightly doped diodes with a wide depletion region, carriers accelerated by the field pick up enough kinetic energy through drift to knock other electrons loose in collisions, building current through impact ionization. This needs a wide region for the carriers to gain speed in.
Step 3: Describe Zener breakdown, which applies here.
A Zener diode is doped heavily on purpose, so its depletion region is very narrow. In such a narrow region a carrier cannot pick up much energy from drift before crossing it. Instead, the field is strong enough that electrons pass straight through the thin barrier by tunneling, a purely quantum effect that does not need the carrier to gain kinetic energy first.
Step 4: Match this to the question.
Since the question names it a Zener diode and asks specifically about its breakdown region, the dominant mechanism is this tunneling process, not drift-driven avalanche multiplication, and not diffusion or ballistic transport, neither of which describes junction breakdown at all.
\[ \boxed{\text{Tunneling}} \]
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