Shockley Diode Calculator

Created: 19/03/2026Updated: 13/06/2026By: Mert
Shockley Diode Calculator
I = IS(eV/(nVT) − 1)
VT = kT/q ≈ 26mV @ 25°C
n = ideality factor (1–2)
Shockley Diode Calculator
V (Diode Voltage)
IS (Saturation Current)
n (Ideality Factor)
T (Temperature °C)
Enter values
Shockley Diode Calculator Results
Diode Current I
—
A
VT (Thermal)
—
mV
Exponent V/(nVT)
—
 
Dynamic Rd
—
Ω
Power P
—
W
Temperature
—
K
Shockley Diode Calculator Input Output

Figure 1: Shockley Diode Calculator — enter values to calculate the result with step-by-step workings.

Table of Contents
Fundamentals
  1. The Shockley Diode Equation
  2. The Parameters
Worked Examples
  1. Silicon Diode at 0.7V
  2. LED at 0.65V (n=2)
  3. Germanium Diode at 0.3V
Reference
  1. Frequently Asked Questions
  2. Related Calculators

The Shockley Diode Equation

The Shockley equation is the fundamental model of every PN junction — diodes, LEDs, solar cells, and the base-emitter junctions inside every BJT. It describes the exponential relationship between voltage and current that makes semiconductor devices work.

I = IS(eV/(nVT) − 1)

VT = kT/q ≈ 25.85 mV at 25°C

The calculator above computes diode current, thermal voltage, the exponent, dynamic resistance, and power from your voltage, temperature, and device parameters. The BJT Gain Calculator builds on this equation — the BJT is two back-to-back PN junctions, and its gain comes from the ratio of currents through these junctions.

The Parameters

IS (saturation current): The reverse leakage current. Typically 10−12 A for silicon, 10−6 A for germanium. Doubles approximately every 10°C.

n (ideality factor): 1 for an ideal junction (diffusion current dominates). 2 when recombination dominates (LEDs, low current). Real diodes: 1–2.

VT (thermal voltage): kT/q = 25.85 mV at 25°C. Increases linearly with absolute temperature. The Emitter Resistor Calculator uses VT indirectly through re = VT/IC, the BJT’s small-signal emitter resistance.

Example: Silicon Diode at 0.7V

V = 0.7 V, IS = 10−12 A, n = 1, T = 25°C

VT = 1.381×10−23 × 298.15 / 1.602×10−19 = 25.69 mV

Exponent = 0.7 / (1 × 0.02569) = 27.25

I = 10−12 × (e27.25 − 1) = 10−12 × 6.81×1011 = 0.681 A

Rd = nVT/I = 25.69m / 0.681 = 37.7 mΩ

At 0.7 V, a typical silicon diode conducts about 680 mA. The dynamic resistance is only 38 mΩ — the junction is a near-perfect conductor at this operating point.

Example: LED at 0.65V (n=2)

V = 0.65 V, IS = 10−14 A, n = 2, T = 25°C

Exponent = 0.65 / (2 × 0.02569) = 12.65

I = 10−14 × e12.65 = 10−14 × 3.13×105 = 3.13 µA

At 0.65 V with n=2, current is microamps — LEDs need higher forward voltage (1.8–3.5 V depending on colour) for visible emission. The ideality factor n=2 reflects recombination in the active region.

Example: Germanium Diode at 0.3V

V = 0.3 V, IS = 10−6 A, n = 1, T = 25°C

Exponent = 0.3 / 0.02569 = 11.68

I = 10−6 × e11.68 = 10−6 × 1.18×105 = 118 mA

Germanium conducts at much lower voltage (0.3 V vs 0.7 V for silicon) because its IS is 106 times larger. The Transistor Base Resistor Calculator uses VBE = 0.3 V for germanium transistors and 0.7 V for silicon.

Frequently Asked Questions

What is the Shockley equation?
I = IS(eV/(nVT) − 1). It describes the exponential I-V curve of any PN junction. Every diode, LED, and transistor base-emitter junction follows this relationship.
What is VT?
Thermal voltage: VT = kT/q ≈ 25.85 mV at 25°C. It increases linearly with temperature. VT appears throughout semiconductor physics — it sets the scale of the exponential.
What is the ideality factor n?
n = 1 for ideal diffusion current. n = 2 for recombination-dominated current (LEDs, low bias). Real silicon diodes: n ≈ 1.0–1.3. Schottky diodes: n ≈ 1.0–1.1. The MOSFET Threshold Voltage Calculator involves a related semiconductor physics parameter (γ).
What is dynamic resistance?
Rd = nVT/I. The small-signal resistance at the operating point. At 1 mA with n=1: Rd = 26 Ω. At 100 mA: Rd = 0.26 Ω. It determines how much the voltage changes for a small current perturbation. The Transistor Biasing Calculator uses re = VT/IC for the same concept in BJTs.
Why does IS matter?
IS sets the voltage at which the diode turns on. Silicon (IS ≈ 10−12) turns on at ~0.7 V. Germanium (IS ≈ 10−6) turns on at ~0.3 V. IS doubles every 10°C, which is why hot diodes conduct more. The MOSFET Calculator uses Vth for the equivalent turn-on parameter.
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Last updated: March 2026