When students first encounter energy bands in semiconductors, and how the properties of simple semiconductor devices such as the p-n junction diode depend on them, the concept can be a bit difficult to grasp. As part of an undergraduate physics course for non-STEM majors that includes semiconductors and simple devices based on the p-n junction, a gravitational analog of the device, using an inclined plane and ball bearings (Fig. 1), has helped students understand the concept. The model has also proved useful in introductory solid-state physics and semiconductor device courses.

1.
V. E.
Henrich
, “
Motivating non-science majors: The technology of electromagnetic waves
,”
Phys. Teach.
56
,
29
(
Jan.
2018
).
2.
See, for example, Sect. 17-1 in
Douglas C.
Giancoli
,
Physics: Principles with Applications
, 7th ed. (
Pearson – Prentice Hall
,
Upper Saddle River, NJ
,
2014
).
3.
See, for example, Sect. 29-9 in
Douglas C.
Giancoli
,
Physics: Principles with Applications
, 7th ed. (
Pearson – Prentice Hall
,
Upper Saddle River, NJ
,
2014
).
4.
The “holes” in this model are 11/16 in in diameter, and the “electrons” are 5/8-in diameter ball bearings. This model is 3 in wide by 22 in long, although the dimensions of the model are arbitrary and not critical. Small hinges connect the n- and p-type regions to the depletion region.
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