The Haynes-Shockley technique for the measurement of electron and hole drift mobility mu in semiconductors is here presented in a version suitable for an. The Haynes-Shockley Experiment. Minority carrier applet and tutorial, which describes generation by laser pulse, diffusion due to nonuniform concentration, drift. The ambipolar drift mobility of holes in n‐type HgCdTe with nominal composition of x= was determined by the Haynes–Shockley experiment.

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Block diagram of the apparatus with optical injection. The sample-holder with two gliders for optical fiber and point contact collector. Example of collected pulses with different values of sweep voltage. Java Applets simulations of the Haynes-Shockley signal: The experiment hxynes in by J.

Shockley to hayness the drift mobility of electrons and holes in semiconductors is conceptually simple. The main difficulties are in the sample preparation, in the charge injection and in the signal detection.

It is an experiment with great educational value, because it allows direct investigation of the drift velocity, of the diffusion process and of the recombination of excess charge carriers. In our new setup the excess carriers are optically injected using internal photoelectric effect avoiding the need of a reliable point-contact emitter.

Setup of the original H-S apparatus.


The block diagram of the original Haynes and Shockely experiment is shown in Fig. As an example, let us consider a P-doped semiconductor bar, of length lwith ohmic contacts soldered at both ends Inside the sample an electric field named sweep field E s is temporarily produced by a pulsed generator, sketched in Figure 1 as a battery in series with a switch.

A simple and instructive version of the Haynes-Shockley experiment

Two point contacts electrodes E and C are made by two metal needled separated by a distance d. The point contacts are partially rectifying and therefore they are drawn as diodes in figure 1 By applying to the electrode E emitter a short negative pulse voltage with an amplitude large enough to forward bias the diode Shockoey Eelectrons will be injected into the crystal region underlying the emitter.

This electron pulse will drift, under the electric field action, with velocity v dand after some time t it will reach the region underlying the electrode C collector. When the excess haymes pulse reaches the point contact C, the minority experimet carrier density is locally increased, thus increasing the inverse current and producing a voltage drop across the resistance R.

On the oscilloscope screen we may observe a first short negative pulse, with amplitude comparable to that of the injection pulse and, after some delay ta second negative pulse, wider and much smaller than the first one. The first peak is simultaneous with the injection pulse: The second pulse corresponds to the excess electon distribution passing under the collector contact: The injected electrons in fact, while drifting towards the collector, diffuse broadening their spatial distribution, so that the width of the collected pulse increases with the time of flight t.


Moreover the electrons recombine with holes so that their number decreases exponentially with time t as: The measurement of the time of flight t.

New version of the Haynes-Shockley experiment. Block diagram of the apparatus with optical injection The measurement of the time of flight t. Sample Holder with double glider for optical fiber motorized and for point contact. Double pulser for the sweep voltage haybes for the laser-driving pulse, with a differential amplifier subtracting the sweep voltage from the collector signal.

Switchable polarity fpr P-doped and N-doped samples.

A simple and instructive version of the Haynes-Shockley experiment – IOPscience

Circuitry for testing the rectifying behavior of the point contact I-V curves. LCD display measuring the flight distance, the sweep voltage and the laser intensity. P-doped Germanium sample with ohmic contacts.

Optional N-doped Germanium sample with ohmic contacts. The Haynes-Shockley experiment requires not included: Simulation 1 Simulation 2.