Visualizing Semiconductor Physics with the SemiSim Simulator

The SemiSim semiconductor simulator provides a visual framework for understanding the movement of charge carriers within transistors. By animating the interaction of electrons and holes, the tool transforms abstract electrical formulas into observable physical behaviors for NPN BJTs, n-channel MOSFETs, and n-channel JFETs.

Visualizing Charge Carrier Dynamics

SemiSim uses a color-coded system to represent the fundamental particles of semiconductor physics: blue dots represent electrons and red dots represent holes. White flashes are used to indicate recombination events, where an electron and a hole annihilate each other.

The simulator offers three distinct levels of visualization to balance clarity and physical accuracy:

Simplified Velocity Mapping

In the primary set of animations, the velocity of charge carriers is calculated by dividing the combined diffusion and drift currents by the total charge. In this mode, diffusion is not explicitly visualized, allowing the viewer to focus on the overall flow of current.

High-Fidelity Diffusion and Drift

For a more accurate representation of physics, the simulator includes animations where carriers undergo both diffusion and drift. While this approach is more physically precise, it is noted as being more visually complex and potentially confusing for beginners.

Terminal Monitoring

To provide quantitative context to the qualitative movement of particles, a set of animations includes probes that display the real-time currents and voltages at each terminal of the transistor.

Supported Transistor Architectures

The simulator provides specific animations for three core transistor types, demonstrating how their internal structures govern current flow:

• NPN Bipolar Junction Transistor (BJT): Visualizes the "hopping" effect of carriers across the base region.
• n-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor): Demonstrates the field-effect control of the conduction channel.
• n-channel JFET (Junction Field-Effect Transistor): Shows the modulation of the channel width via the gate junction.

Educational Impact and Community Feedback

Electrical engineering students and professionals have noted that these visualizations bridge the gap between mathematical formulas and conceptual understanding.

"I have an EE education, but I didn't really understood what charges were doing in a BJT. I can use them and apply the formulas, but I never really 'grokked' them. This makes it clearer."

Other users have suggested expanding the tool to include vacuum tubes (triodes, tetrodes, and pentodes) to compare the difference between current-controlled devices like BJTs and voltage-controlled devices like FETs. Additional requests include the addition of layman-friendly explanations for each animation and the integration of 3D models to better represent the physical volume of the semiconductor material.