A classic solid-state experiment that demonstrates the drift and diffusion of charge carriers in a semiconductor. The experimental arrangement is shown in the diagram. A voltage is placed across the length of a bar of n-type semiconductor (for example) to create a drift field. Minority carriers, holes in this example, are injected at one end of the bar in a narrow pulse, using either a pulse of light to photogenerate the carriers or a short voltage pulse at a rectifying point contact. The injected minority carriers will drift along the bar at the drift velocity associated with the applied electric field. The carriers will also diffuse away from each other, causing the pulse to broaden. The pulse is detected at the downstream end of the bar using a voltage probe – usually another point contact. The broadening of the pulse can be measured and the diffusion of the carriers determined. From these measurements the minority carrier drift mobility and diffusion constant can be calculated.

Haynes–Shockley experiment: minority holes in an n-type semiconductor

https://www.youtube.com/watch?v=zYGHt-TLTl4 Historic footage of Professors Haynes and Shockley explaining their experiment