hover the die for a live readout — paint with the left button, erase with the right
▮ SILICON SANDBOX
A 2D drift–diffusion simulator: Poisson + Scharfetter–Gummel carrier transport on a grid.
Paint a device out of silicon, oxide and metal, attach voltage probes, and watch potential,
carriers and current respond live.
Painting
Pick a material, then left-drag on the die to paint; right-drag erases to vacuum.
Painted regions start at charge-neutral equilibrium.
Probes
In Probe mode, click anywhere to attach a voltage terminal (ohmic contact on silicon; equipotential on metal).
Click a probe to select it, drag the voltage slider; click it again or press ⌫ to remove.
The chip list shows each probe's live terminal current.
Doping brush
The Dope tool paints net doping into any semiconductor cell (Si, Ge, GaAs) without changing the material —
pick N or P and a concentration, then drag. Right-drag resets cells to intrinsic. Graded and asymmetric junctions welcome.
The Advanced doping sliders re-dope all cells of the four named Si materials and overwrite brushed values there.
Contacts & Schottky
Each probe can be Ohmic (carriers pinned to doping equilibrium) or Schottky: the surface is pinned to the
metal's Fermi level offset by the work function W (Advanced) — with W < 0 on N-type silicon a single contact rectifies
like a diode, no PN junction needed.
Logic presets
NAND, AND, OR, XOR and the full adder are real circuits: ratioed-NMOS stages with silicon pull-up
resistors, floating output nodes, and (XOR/adder) buried N+ crossunders. ▸ amber tags mark input
terminals — set them to 0 / +48 via the chips (same-letter chips are one net and move together).
Green tags mark outputs with their live node voltage. Internal nets show gray ≈ tags.
I–V plotter
Sweeps one probe and plots the current read at another, live: sweep G / read D gives the NMOS transfer curve,
sweep D / read D the output curve, sweep A / read A the diode I–V. Toggle log |I| for subthreshold slopes.
Materials note
Ge and GaAs implement per-material nᵢ and mobilities (ratios to Si: μₙ 2.8× / 6.1×). Their nᵢ ratios are compressed
(40 and 0.02 vs the physical 2.4·10³ and 2·10⁻⁴) so junctions stay resolvable on this grid; interfaces to Si are
nᵢ-heterojunctions only — no band-offset physics.
Save / load layout stores materials, per-cell doping and probes as JSON.
Reading the views
ψ — electrostatic potential (diverging map). log n / log p — carrier densities, log scale.
net charge — space charge; depletion regions show as colored bands.
|J| & particles — conduction current; particles ride the actual computed J field.
Keys
Space play/pause · S step · R reset · 1..8 materials ·
B paint · P probe · ⌫ delete probe · ? help · Esc close