Electronics

Diodes & Transistors

Pick a device, turn the supply up and watch the two kinds of charge that run every chip: electrons and the holes they leave behind. A diode is a one-way valve, a transistor is a valve with a knob, and both are doped silicon with a barrier you can raise and lower.

electronsholes

The pale circled charges are dopant ions bolted into the crystal: they never move, they only set up the built-in field

Current—

—

Device

Supply V_S 2.0 V

reverseforward

Series resistor 1.0 kΩ

10 Ω100 kΩ

Doping N 1.0e16 cm⁻³

lightheavy

Temperature 300 K

coldhot

Display

Time rate 1.0×

Show fixed dopant ions

Values

Current—

Across the device—

Control input—

Operating region—

Barrier—

Measured—

Power in the device—

What to observe

Forward bias the PN diode: the depletion region between the two crowds shrinks, carriers cross, and every crossing ends in a recombination flash. Reverse it and the region swells until only a picoamp leak is left.
Switch the LED between colours: red turns on near 1.9 V, blue near 2.9 V. The forward drop is the band gap, and the band gap is the colour.
On the NPN, a trickle of base current lets a flood of electrons cross into the collector, about β times as many. Raise I_B far enough and V_CE hits the floor: that is saturation, the switch fully on.
On the NMOS, a gate above V_th pulls an inversion layer of electrons under the oxide while no current enters the gate. With a high drain voltage the channel pinches off and the current stops caring about V_DS.

Shortcuts:space run/pause · s step · r reset · f fullscreen