University of Illinois at Urbana-Champaign
Office for Mathematics, Science, and Technology Education
College of Education @ University of Illinois

Hole Flow

In a sense, there really is something that moves from positive to negative while the electrons are moving the other way. The hole that the electron leaves behind as it moves toward the positive charge can be thought of as moving toward the negative charge.

The large circles in the illustration below represent atoms, with positive charges in the middle and negative electrons around the outside. When the electron is in the atom, the whole thing is neutral (green) because the positive and negative parts balance out. When the electron leaves, the remaining atom is positive (red). The hole is wherever you see a red atom, which is missing its outermost electron. (All the other electrons are in that middle circle with the protons, because we aren't interested in them right now.) As the electrons move one way, from negative to positive, the holes move the other way, from positive to negative.

You can think about current as the flow of electrons, which go from negative to positive, or as the flow of holes, which go the other way. If you are reallly into semi-conductor theory it makes a difference which one you use, but otherwise you aren't likely to care. We usually use hole flow because the direction agrees with the decision that the early scientists made when they had to pick a direction to use in their calculations. It's traditional.

This applet was written by Lisa Denise Murphy at the University of Illinois. Early drafts were written in 1999. The current version was last revised in January of 2000. Permission is given for students and teachers to use this applet, provided acknowledgement is made of the source. Anyone interested in using this applet in connection with any published paper or commercial venture should please first consult the author. Thank you.

This page last revised January 19, 2000.


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