The experiment measures the drift mobility of electrons and holes in semiconductors is conceptually simple.

The Haynes-Shockley experiment describes the motion of minority carriers in a semiconductor. By measuring the time it takes for a LED to ionize a Silicon bar applied with a known drift voltage, we can calculate using an oscilloscope and a voltmeter the drift velocity, electric field, mobility and lifetime of minority carriers (in our n-type bar, holes).

Let us consider a p-doped semiconductor bar, of length l, with ohmic contacts soldered at both ends.

Two point contacts E and C are made. These contacts are partially rectifying and hence shown as diodes in figure.

A short negative pulse of amplitude large enough to forward bias the diode $D_E$ is applied to the electrode E (emitter). So the electrons will be injected into the crystal region underlying the emitter.

This electron pulse will drift, under the electric field action, with velocity and after some time t it will reach the region underlying the electrode C (collector).

When the excess electron pulse reaches the point contact C, the minority charge carrier density is locally increased, thus increasing the inverse current and producing a voltage drop across the resistance R. it is shown on CRO.

Initial time of pulse as well as arrival time of center of received pulse is noted down. Time taken by pulse determines the drift mobility.