PN junctions and diodes

How does the forward voltage of a silicon diode carrying a constant current change as the temperature rises?

  1. AIt falls at about 2 mV/°C
  2. BIt rises at about 2 mV/°C
  3. CIt does not change
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Answer: A. It falls at about 2 mV/°C

The forward voltage of a silicon diode at constant current drops by about 2 mV for every 1 °C rise. The intrinsic carrier density increases with temperature, so less voltage is needed to pass the same current. This property is also used in temperature sensors.

  • A. Correct. Its temperature coefficient is about −2 mV/°C.
  • B. The forward voltage falls, not rises, as temperature increases.
  • C. The forward voltage has a clear temperature dependence.
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More PN junctions and diodes questions

  1. For an ideal diode (ideality factor n = 1) at room temperature, roughly how much must the forward voltage increase to raise the forward current tenfold?
  2. Which expression gives the depletion (junction) capacitance C of a reverse-biased PN junction in terms of junction area A, depletion width W and semiconductor permittivity ε?
  3. Why does no current flow externally in a PN junction in thermal equilibrium?
  4. Which is the correct definition of the fill factor (FF) of a solar cell?
  5. Roughly what is the small-signal (dynamic) resistance of an ideal silicon diode carrying a forward current of 1 mA at room temperature? (kT/q ≈ 26 mV)