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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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. The block diagram of the original Haynes and Shockely experiment is shown in Fig. The first peak is simultaneous with the injection pulse: As an example, let us consider a P-doped haynew bar, of length lwith ohmic contacts soldered at both ends Inside the sample an electric field named sweep field E s is temporarily produced hxynes a pulsed generator, sketched in Figure 1 as a battery in series with a switch.
This page was last edited on 21 Marchat Block diagram of the apparatus with optical injection The measurement of the time of flight t. From Wikipedia, the free encyclopedia.
The first term of the equations is shlckley drift currentand the second term is the diffusion current. Two point contacts electrodes E and C are made by two metal needled separated by a distance d. This can be interpreted as a Dirac delta function that is created immediately after the pulse.
Example of collected pulses with different values of sweep voltage.
To see the effect, we consider a n-type semiconductor with the length d. 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.
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. New version of the Haynes-Shockley experiment. We are interested in determining the mobility of the carriers, diffusion constant and relaxation time.
Double pulser for the sweep voltage and for the laser-driving pulse, with a differential amplifier subtracting the sweep voltage from the collector signal. We consider the continuity equation:.
Subscript 0s indicate equilibrium concentrations.
Block diagram of the apparatus with optical injection. The semiconductor behaves as if there were only holes traveling in it. The signal then is Gaussian curve shaped.
The second pulse corresponds to the excess electon distribution passing under the collector contact: Optional N-doped Germanium sample with ohmic contacts. 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 D Eelectrons will be injected into the crystal region underlying the emitter.
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. 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. Moreover the electrons recombine with holes so that their number decreases exponentially with time t as: The measurement of the time of flight t.
The sample-holder with two gliders for optical fiber and point contact collector. The two initial equations write:. Retrieved from ” https: In semiconductor physicsthe Haynes—Shockley experiment was an experiment that demonstrated that diffusion of minority carriers in a semiconductor could result in a current.
Simulation 1 Simulation 2. In shocckley new setup the excess carriers are optically injected using internal photoelectric effect avoiding the need of a reliable point-contact emitter. In the experiment, a piece of semiconductor gets a pulse of holesfor example, as induced by voltage or a short laser pulse. Bell System Technical Journal.
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Views Read Edit View history. The Haynes-Shockley experiment requires not included: Sample Holder with double glider for optical fiber motorized and for point contact.
In the following, we reduce the problem to one dimension. However, as electrons and holes diffuse at different speeds, the material has a local electric charge, inducing an inhomogeneous electric field which can be calculated with Gauss’s law:.
Shockley to measure the drift mobility of electrons and holes in semiconductors is conceptually simple. Java Applets simulations of the Haynes-Shockley signal: Setup of the original H-S apparatus. 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.