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Nikozil P-doped Germanium sample with ohmic contacts. The semiconductor behaves as if there were only holes traveling in it. In the experiment, a piece of semiconductor gets a pulse of holesfor example, as induced by voltage or a short laser pulse. The first peak is simultaneous with the injection pulse: New version of the Haynes-Shockley experiment. We are interested in determining the mobility of the carriers, diffusion constant and relaxation time.
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. The measurement of the time of flight t.
To see the effect, we consider a n-type semiconductor with the length d. Double pulser for the sweep voltage and for the laser-driving pulse, with a differential amplifier subtracting the sweep voltage from the collector signal. From Wikipedia, the free encyclopedia.
The first term of the equations is the drift currentand the second term is the diffusion current. Simulation 1 Simulation 2. On the oscilloscope screen shockleu 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. 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 Two point contacts electrodes E and C are made by two metal needled separated by a distance d.
Circuitry for testing the rectifying behavior of the point contact I-V curves. 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 haybes diode D Eelectrons will be injected into the crystal region underlying the emitter.
The signal then is Gaussian curve shaped. The block diagram of the original Haynes and Shockely experiment is shown in Fig. Subscript 0s indicate equilibrium concentrations. The Haynes-Shockley experiment requires not included: The injected electrons in fact, while exeriment towards the collector, diffuse broadening their spatial distribution, so that the width of the collected pulse increases with the time of flight t.
Holes then start to travel towards the electrode where we detect them. Setup of the original H-S apparatus. Sample Holder with double glider for optical fiber motorized and for point contact. Example of collected pulses with different values of sweep voltage. This electron pulse will drift, under the electric field action, with velocity v dand after experimenr time t it will reach the region underlying the electrode C collector.
Moreover the electrons recombine with holes so that their number decreases exponentially with time t as: This page was last edited on 21 Marchat Optional N-doped Germanium sample with ohmic contacts. This can be interpreted as a Dirac experinent function that is created immediately after the pulse. 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.
Block diagram of the apparatus with optical injection The measurement of the time of flight t. The second pulse corresponds to the excess electon distribution passing under the collector contact: In our new setup the excess carriers are optically injected using internal photoelectric effect avoiding the need of a reliable point-contact emitter. The two initial equations write:. Switchable polarity fpr P-doped and N-doped samples. LCD display measuring the flight distance, the sweep voltage and the laser intensity.
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. Views Read Edit View history. We consider the continuity equation:. The experiment proposed in by J. TOP Related Posts.
EV Haynes-Shockley Experiment
New version of the Haynes-Shockley experiment The experiment proposed in by J. Haynes and W. Shockley to measure 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.