PN junctions and diodes

Zener diodes with a Zener voltage of about 5 to 6 V show little change in voltage with temperature. Why?

  1. ABecause the band gap of silicon does not change with temperature
  2. BBecause no current flows through the diode at this voltage
  3. CBecause tunneling (Zener) breakdown, with a negative temperature coefficient, and avalanche breakdown, with a positive one, occur to similar degrees and cancel
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Answer: C. Because tunneling (Zener) breakdown, with a negative temperature coefficient, and avalanche breakdown, with a positive one, occur to similar degrees and cancel

Diodes with low breakdown voltages (below about 5 V) break down mainly by tunneling (Zener breakdown), and their breakdown voltage falls as temperature rises. Higher-voltage ones break down mainly by avalanche, and their breakdown voltage rises with temperature. Around 5 to 6 V, the two effects work to similar degrees and the temperature coefficient is nearly zero.

  • A. Silicon's band gap does change slightly with temperature.
  • B. A Zener diode is used by passing current in its breakdown region.
  • C. Correct. Two breakdown mechanisms with opposite temperature coefficients cancel.
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