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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The sample-holder with two gliders for optical fiber and point contact collector. Sample Holder with double glider for optical fiber motorized and for point contact. On the oscilloscope screen we shoclley 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 point contacts are partially rectifying and therefore they experikent 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 D Eelectrons will be injected into the crystal region underlying the emitter.
Ehockley the following, we reduce the problem to one dimension. In semiconductor physicsthe Haynes—Shockley experiment was an experiment that demonstrated that diffusion of minority carriers in a semiconductor could result in a current.
Optional N-doped Germanium sample with ohmic contacts. As an example, let us consider a P-doped semiconductor bar, of length lwith ohmic contacts soldered at experimenf 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.
Example of collected pulses with different values of sweep voltage. New version of the Haynes-Shockley experiment.
This page was last edited on 21 Marchat Simulation 1 Simulation 2. Switchable polarity fpr P-doped and N-doped samples. The first term of the equations is the drift currentand the second term is the diffusion current. Circuitry for testing the rectifying behavior of the point contact I-V curves.
In the experiment, a piece of semiconductor gets a pulse of holesfor example, as induced by voltage or a short laser pulse. Two point contacts electrodes E and C are made by two metal needled separated by a distance d. Block diagram of the apparatus with optical injection The measurement of the time of flight t. Bell System Technical Journal.
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hayhes To see the effect, we consider a n-type semiconductor with the length d. P-doped Germanium sample with ohmic contacts. Java Applets simulations of the Haynes-Shockley signal: The experiment was reported in a short paper by Haynes and Shockley in with a more detailed version published by Shockley, Pearson, and Haynes in Views Read Edit View history.
We are interested in determining the mobility of the carriers, diffusion constant and relaxation time. However, as electrons and holes diffuse at different speeds, the material has ahynes local electric charge, inducing an inhomogeneous electric field which can be shockldy with Gauss’s law:. 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 sockley drop across the resistance R.
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. We consider the continuity equation:. Double pulser for the sweep voltage and for the laser-driving pulse, with a differential amplifier subtracting the sweep voltage from the collector signal.
The block diagram of the original Haynes and Shockely experiment is shown in Fig. Moreover the electrons recombine with holes so that their number decreases exponentially with time t as: Retrieved from ” https: This can be interpreted as a Dirac delta function that is created immediately after the pulse. From Wikipedia, the free encyclopedia. Setup of the original H-S apparatus. The Haynes-Shockley experiment requires not included: In our new setup the excess carriers are optically injected using internal photoelectric effect avoiding the need of a reliable shockey emitter.
The semiconductor behaves as if there were only holes traveling in it. The first peak is simultaneous with the injection pulse: 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. Block diagram of the apparatus with optical injection.
The main difficulties are in the sample preparation, in the charge injection and in the signal detection. Subscript 0s indicate equilibrium concentrations. Holes then start to travel towards the electrode where we detect them.
The signal then is Gaussian curve shaped. The measurement of the time of flight t.
A simple and instructive version of the Haynes-Shockley experiment – IOPscience
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. The two initial equations write:. The experiment proposed in by J.