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Diodes and LEDs (PN Junction Basics)

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Figures (4)

Figure A. A p–n junction in thermal equilibrium with zero bias voltage applied. Electron and hole concentration are reported with blue and red lines, respectively. Gray regions are charge-neutral. Light-red zone is positively charged. Light-blue zone is negatively charged. The electric field is shown on the bottom, the electrostatic force on electrons and holes and the direction in which the diffusion tends to move electrons and holes. (The log concentration curves should actually be smoother with slope varying with field strength.)
A p–n junction diode in low forward bias mode. The depletion width decreases as voltage increases. Both p and n junctions are doped at a 1e15/cm3 doping level, leading to built-in potential of ~0.59V. Observe the different quasi Fermi levels for conduction band and valence band in n and p regions (red curves).
Silicon atoms (Si) enlarged about 45,000,000x (Image size approximately 955 pm × 955 pm)
Figure B. A p–n junction in thermal equilibrium with zero bias voltage applied. Under the junction, plots for the charge density, the electric field, and the voltage are reported. (The log concentration curves should actually be smoother, like the voltage.)

Key Points

  • A diode is a two-terminal electronic component that conducts electric current primarily in one direction (asymmetric conductance).
  • An LED strip light is a flexible circuit board populated by surface-mount LEDs and other components that usually comes with an adhesive backing.
  • In forward bias, the p-type is connected with a positive electrical terminal and the n-type is connected with a negative terminal.
  • With forward bias, the depletion region is narrow enough that electrons can cross the junction and inject into the p-type material.
  • The electron shell configurations for 29 of the first 36 elements are listed in Table 2.2.
  • For each electron–hole pair recombination made, a positively charged dopant ion is left behind in the N-doped region, and a negatively charged dopant ion is created in the P-doped region.

Terms

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