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GATE 2016 EC (EC3) – Question 20

Electronic Devices · P-N Junction and Semiconductor Devices · 1 mark · Multiple choice

The room-temperature I–V curves of diodes made from materials X,Y,Z are shown. They are uniformly doped and otherwise identical. With material band gaps $E_{gX},E_{gY},E_{gZ}$, which relation holds?

Diagram for GATE 2016 EC (EC3) question 20
  1. $E_{gX}>E_{gY}>E_{gZ}$
  2. $E_{gX}=E_{gY}=E_{gZ}$
  3. $E_{gX}<E_{gY}<E_{gZ}$
  4. No relationship exists.

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Show answer and explanation

Correct answer: (C) $E_{gX}<E_{gY}<E_{gZ}$

Explanation

For otherwise comparable junctions, a larger band gap reduces intrinsic carrier concentration and reverse saturation current. A larger forward voltage is then required to obtain the same current.

At any fixed positive current on the plotted curves, X requires the least voltage, Y an intermediate voltage and Z the greatest. Thus the band gaps rise in the same order: **$E_{gX}<E_{gY}<E_{gZ}$, C**.

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