Diode Physics & Characteristics Visualization

Operating point

Compare at this bias

Same applied voltage, temperature and current-model setting. Each device uses its own saved properties.

Device	Current	Junction Vⱼ	Width W	Cⱼ

One position axis · aligned depletion boundaries

Inside the model · equations & learning guide

Compare diode characteristics

The modes represent a silicon PN junction, a metal / n-silicon Schottky contact, and a heavily doped silicon Zener junction. Each mode retains its own device properties. Applied voltage, temperature, and current-model selection are shared. Compare diode types overlays the saved examples at the same voltage and temperature.

Compare	PN junction	Schottky	Zener example
Junction	p-type and n-type silicon	Metal and n-type silicon	Heavily doped p-type and n-type silicon
Forward I–V curve	Current rises smoothly with forward voltage	Lower forward voltage at a given current for these defaults	PN-like forward behavior
Reverse I–V curve	Small leakage before breakdown	Greater leakage for these defaults	Strong reverse current near the selected breakdown voltage
Depletion region	Extends into both semiconductor regions	Extends into n-type silicon	Narrower at a given junction voltage because of heavier doping
Capacitance plots	Depletion capacitance and forward stored-charge capacitance	Depletion capacitance; modeled diffusion capacitance is zero	Depletion capacitance and forward stored-charge capacitance

Compare forward voltage at a stated current and temperature. Area and the saved device properties also affect the result. In reverse breakdown, the voltage changes with current according to the shape of the modeled knee and the series resistance.

01 / Junction structure and bias

PN junction. Donors supply electrons to n-type silicon; acceptors make holes abundant in p-type silicon. When the regions meet, mobile charges spread across the boundary and recombine. Fixed negative acceptor ions remain on the p side and positive donor ions on the n side. These ions form the depletion region and its built-in electric field. Forward bias lowers the internal barrier and narrows this region; reverse bias raises the barrier and widens it.

V_{T} = \frac{k_{B} T}{q}

V_{bi} = V_{T} \ln (\frac{N_{A} N_{D}}{{n_{i}}^{2}}) PN / Zener

N_A and N_D are the acceptor and donor concentrations; n_i is the intrinsic carrier concentration. The thermal voltage V_T is approximately 25.9 mV at 27 °C. At equilibrium, the built-in field balances the tendency of charges to spread, giving zero net terminal current. Purdue · PN junctions

Schottky contact. A metal replaces the p-type region. Negative charge at the metal surface balances the positive donor ions in depleted n-type silicon. The selected metal barrier property affects the band bending and current. With the default properties, the Schottky example shows a lower forward drop and greater reverse leakage.

Zener junction. Heavier doping produces a narrower depletion region and a stronger electric field. The selected breakdown voltage sets where the reverse I–V curve turns downward. Its forward curve follows the same form as the PN example.

02 / Connect charge, field, and depletion width

All five diagrams share the same horizontal position axis and depletion edges. The junction is at x = 0. Follow an edge vertically to connect the depleted material with its energy bands, charge density, field, and potential. Each vertical axis uses its own scale.

Δψ = V_{bi} - V_{j}

W = \sqrt{\frac{2 ε_{Si}}{q} (\frac{1}{N_{A}} + \frac{1}{N_{D}}) Δψ} PN / Zener

x_{p} = \frac{W N_{D}}{N_{A} + N_{D}}, x_{n} = \frac{W N_{A}}{N_{A} + N_{D}}

W = x_{n} = \sqrt{\frac{2 ε_{Si} Δψ}{q N_{D}}} Schottky

V_j is the internal junction voltage; Δψ is the potential rise across the depleted region. In PN and Zener modes, the depletion width extends farther into the more lightly doped side. In Schottky mode, the width lies in the semiconductor, and the metal charge appears as a sheet at the interface.

\frac{d E}{d x} = \frac{ρ}{ε_{Si}}, E = - \frac{d ψ}{d x}

| E_{\max} | = \frac{q N_{D} x_{n}}{ε_{Si}}

Charge density ρ sets the slope of the electric field E. The field points left, from the positive donors toward the negative charge. The field plot therefore lies below zero; its peak readout gives the magnitude. Potential ψ rises toward the right, while electron band-edge energy falls. MIT · charge, field, and potential

03 / Read the energy bands

E_C and E_V mark the conduction- and valence-band edges. They bend together and remain separated by the model's silicon band gap of 1.12 eV. The purple dotted E_fi curve is the intrinsic Fermi level, a reference associated with undoped semiconductor. It lies near the middle of the gap and follows the band bending.

The dashed Fermi references describe the two sides of the junction. They coincide at equilibrium and separate by the energy associated with V_j under bias. These side references show the contact conditions. Forward bias reduces band bending; reverse bias increases it. In Schottky mode, the semiconductor bands occupy the right-hand region, and the shaded metal states appear on the left.

04 / Read the current–voltage curves

I_{base} = I_{S} [\exp (\frac{V_{j}}{n V_{T}}) - 1]

I = I_{base} + I_{breakdown}

V = V_{j} + I R_{s}

Forward current rises approximately exponentially at first. I_S sets the current scale for the selected diode, and n is the ideality factor. At higher current, the voltage drop across R_s makes the terminal I–V curve less steep. The Intrinsic selection uses the base current law with V_j equal to V. + R_s & breakdown adds series resistance and the reverse-breakdown branch.

On a logarithmic current axis, equal vertical intervals represent equal current ratios. The plot uses the magnitude |I|, while the operating-point readout retains the sign. Positive current corresponds to forward operation; negative current corresponds to reverse operation.

The BV property sets the onset of the illustrative reverse knee. In the Zener example, the added reverse branch reaches −1 mA when the internal reverse voltage exceeds BV by 0.10 V. BV is a separate adjustable property: doping controls the depicted depletion width and field, while BV controls the electrical knee. The breakdown property stays fixed as temperature changes.

05 / Read resistance and capacitance

r_{d} = \frac{\partial V}{\partial I}, C_{j} = \frac{ε_{Si} A}{W}

C_{diff} \approx τ \frac{\partial I_{base}}{\partial V_{j}} PN / Zener, forward bias

C_{diff} = 0 Schottky model

Small-signal resistance r_d is the local slope of voltage against current at the operating point. In the + R_s & breakdown model, it includes the series resistance. Junction capacitance C_j describes the change in depletion charge: a wider depleted region gives a smaller capacitance, and a larger junction area A gives a larger capacitance.

The diffusion-capacitance plot represents additional stored charge in forward-biased PN and Zener junctions. The lifetime τ controls how much charge accumulates at a given base-current slope. Both capacitance plots describe the internal junction under slowly varying conditions. The Schottky example stores depletion charge through C_j.

06 / Read temperature and animation

The current-versus-temperature plot holds the selected terminal voltage fixed. Temperature changes V_T, the intrinsic carrier concentration, the current scale, and the built-in potential. The saved ideality factor, series resistance, lifetime, Schottky barrier, breakdown property, and silicon band gap remain fixed.

v_{marker} = 80 \frac{px}{s} \times \frac{| I |}{1 mA}

Moving markers represent net terminal current at the fixed scale 1 mA → 80 pixels/s. Doubling the current doubles their speed. Electrons move opposite conventional current; holes move with it. At equilibrium the markers stop as the opposing microscopic motions balance. Tiny leakage can look stationary, and large currents can produce jumps between frames. Marker counts and sizes are illustrative.

07 / Supported model range

The diagrams use uniformly doped silicon, a fixed 1.12 eV band gap, and the depletion approximation. They show steady operating points at the selected temperature. The current curves and reverse knees illustrate the chosen device properties; quantitative comparison with a physical diode requires its measured parameters.

Watch the validity notice. Depletion width, junction capacitance, and the spatial profiles are shown where the remaining barrier exceeds 50 mV and, for PN and Zener junctions, the estimated excess carrier density stays below 10% of the majority density. The diffusion-capacitance curve also ends at this density limit. Outside the depletion range, the diagram reports that the approximation is unavailable, and the selected current curve continues as an amber extrapolation. These thresholds indicate where the teaching approximation is used; a physical diode changes continuously through these conditions.