DopingMVP
PN junction explorer
See conceptually how the depletion region of a PN junction changes as you vary the doping on each side.
Inputs
Qualitative — not to scale
This shows trends only (how the depletion region grows, shrinks, and shifts with doping). It does not compute an exact depletion width, which also depends on the junction voltage.
P
N
P region Depletion region N region
Interpretation
Where P meets N, carriers recombine and leave a carrier-free depletion region. Two trends: (1) heavier doping on both sides makes the depletion region narrower; (2) the depletion extends further into the more lightly-doped side (charge balance means Nₐ·xₚ = N_d·xₙ). With equal doping the depletion is symmetric.
Formula
Nₐ·xₚ = N_d·xₙ · W ∝ √(1/Nₐ + 1/N_d)
Trends only; exact width also needs the junction voltage.
Variables
| Symbol | Variable | Unit |
|---|---|---|
| Nₐ | Acceptor (P-side) doping | m⁻³ |
| N_d | Donor (N-side) doping | m⁻³ |
| xₚ, xₙ | Depletion widths into P and N | m (relative here) |
| W | Total depletion width | m (relative here) |
Assumptions & validity
This tool assumes:
- Abrupt junction; qualitative trends only.
- Widths are relative/illustrative, not computed in absolute units.
- Ignores applied bias; the real width also depends on the junction voltage.
Worked example
Make Nₐ ≪ N_d (lightly-doped P side).
The depletion region widens and reaches much further into the P side.