<p><br></p><div class="text-justify">

<p>We must know first that <b>The electrical conductivity (σ)</b>, is not more than the ability to conduct the electric current when a potential difference, that is to say a voltage, is applied to it. It is without a doubt one of the most important physical properties in a semiconductor or a solid. In a sample of a totally homogeneous semiconductor, this depends on the concentration and mobility of the charge carriers.</p>

<p>There are different types of techniques to characterize materials, one of the most important in the area of semiconductors is the electrical resistivity, since it provides us with essential information about the activation energy and the concentration of the main charge carriers (electrons, type n, holes, type p).</p>

<p>Some of the experiments that gives us a very important information about the activation energy and the concentration of the major charge carriers (electrons, type n, gaps, type p) is the measure of the electrical resistivity and the effect of Hall in function of the temperature. In said experimental methods what is circulated electric current (I) by a semiconductor bar to which electrical contacts are made, as shown in the following figure. It should be noted that this time we will focus on talking about the 4-point method, later we will learn about the 6-point or contact method used to measure the Hall effect.</p>

<center> <img src="https://cdn.steemitimages.com/DQmVSkcBBYvctVtu2Ed6Efqf2jTwg3fdC4hU64cjzuHYzEP/image.png"><br><sup><b>Experimental scheme of bar method or 4 points</b></sup></center>

<h3>But what is electrical resistivity?</h3>

<blockquote>Is responsible for quantifying the force with which a given material is opposed to the flow of electrical current. A low resistivity indicates a material that easily allows the movement of electric charge. The metals of low resistance, for ex. copper, they require more currents to produce the same amount of heat. The materials of low resistance also exhibit a low constant resistance.</blockquote>

<p>The electrical resistivity measurements is the most fundamental of the measurements of routines that are made in semiconductor crystals. Basically, any type of measurement is done by passing through the sample a known amount of current with an exact precision, and measuring the voltage drop between two points separated by a known distance.</p>

<p>It is important to know that the electrical resistivity of a material is used in its fullness for the quality control of various products manufactured with semiconductor materials. In principle they were applied to 2 of the main known semiconductors, which were the precursors for a wide range of new materials such as silicon and germanium, due to the great results shown by these two materials, it was decided to experiment with others and the results They were excellent, and thanks to that, today they have been a fundamental part of the technological advances in the area of materials.</p>

<p>Now, we will focus on the importance of knowing the technique of <b>electrical resistivity applying the method of 4 points or contacts</b>.</p>

<p>First of all we must obtain a semiconductor ingot by means of a growth synthesis, and then prepare it so that it has a parallelepiped shape (figure 1).</p>

<center> <img src="https://cdn.steemitimages.com/DQmPWKbjLCcVkbArnK5TWxH9T83Y2h1LTkh64Sx7vrbmWrV/image.png"><br><sup><b>Figure 1. Diagram of a parallelepiped</b></sup></center>

<p>After having the parallelepiped, one should look for a Bakelite and mount the semiconductor sample on it. As we know Bakelite is an insulating plastic that supports high temperatures, the purpose of mounting the sample in this material is that when making measurements at high temperatures, the material does not disintegrate and keep the semiconductor intact and without deformations.</p>

<center> <img src="https://cdn.steemitimages.com/DQmbiy1HWpTKNRR1Kndj5hMXcwvHi89YPmnc3pZpiyDC862/image.png"><br><sup><b>Figure 2. Diagram of a semiconductor in the form of a parallelepiped on a bakelite</b></sup></center>

<p>It is important to take into consideration an extremely important aspect and that is that the sample must be totally clean and free of corrosion agents, that is to say we must polish the surface of the sample until a bright tone is present, the objective of this process is that At the moment of making the measurements, we do not present significant errors due to dirt or deformity in the sample or any other type of impurity.</p>

<p>The next step is to weld 4 copper wires on the surface of the sample, specifically on its sides (right, left, top and bottom) as shown in figure 3.</p>

<p><b>But why copper wires?</b>, the answer is simple, we all know the ability to drive current that has an element such as copper, but the best feature of this material is the easy adhesion it has to different semiconductor materials, either pure or composed of several elements. A very thin almost imperceptible copper wire is the correct one to weld to the semiconductor sample. Small pieces of indium should be used, which would be the material that will make the union (copper-semiconductor) and with a captive at a suitable temperature that reaches the melting point of the indian so that it melts, adheres to the sample (figure 3). ).</p>

<center> <img src="https://cdn.steemitimages.com/DQmWarQHYwfnZnEyV2xnuJeqErVYPxj1VjBqvX4gwrNqejs/image.png"><br><sup><b>Figure 3. Diagram of the semiconductor in Bakelite with the copper wires adhered to the sample</b></sup></center>

<p>Subsequently to the bakelite other copper wires of a greater thickness must be connected. Through these wires are connected the respective current cables and the voltage that send the signal to the equipment that records the measurement data. Bakelite is used as an insulator and as a guide to work comfortably and obtain accurate measurements.</p>

<center> <img src="https://cdn.steemitimages.com/DQmczWwBbVxBqfs5eUJrURbzS1X9aDupBKLJU4gLkKuBEfp/image.png"><br><sup><b>Figure 4. Diagram of the semiconductor in Bakelite with copper wires where current and voltage circulate</b></sup></center>


<center> <img src="https://cdn.steemitimages.com/DQmew2L1c5Y92Zb7eHXmQ6LM6GCu9GzGP3dMNmi5iYm5rJ5/image.png"><br><sup><b>Figure 5. Real assembly of the semiconductor sample for the measurements of electrical resistivity and hall effect at the end of the bar or 4-point method</b></sup></center>

<p>It is important to note that the sample of the semiconductor material that is to be characterized by means of this experimental method must have certain considerations regarding its size, for example the material shown in the photo has a diameter of 1.5cm in length, 0.75. cm wide and 0.20cm high. This also brings certain limitations at the time of assembly since it is quite difficult to work with samples of this size, it is advisable to work with a microscope to be able to observe in detail when making contacts on the sample.</p>

<p><i>So far I just want to show you this little process, I will explain later the 6-point or contact method used to measure the hall effect and in turn the equations involved in the process for the calculation of electrical resistivity as a function of temperature.</i></p>

<h3>If you want more information about the subject you can visit the following links:</h3>

<a href="https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity">Electrical resistivity and conductivity
</a>

<a href="https://www.electronics-tutorials.ws/diode/diode_1.html">Semiconductor Basics</a>

<a href="https://www.electronics-tutorials.ws/resistor/resistivity.html">Resistivity</a>

<a href="https://www.academia.edu/20228485/Measurement_of_Semiconductor_Parameters">Measurement of Semiconductor Parameters</a>

<p></p><li>Marin, G. (2001). Preparación para diferentes técnicas, estudios comparativos de las propiedades ópticas y eléctricas en función de la temperatura de los semiconductores CuInTe2 y CugaTe, Tesis de Maestría. Mérida, Universidad de los Andes.</li><p></p>

<p></p><li>ASTMF43-09. International. (2011). Standard (2010) Test methods for resistivity of semiconductor materials Vol 10.05.</li><p></p>

<center><h4> Publish through our official app and you will get an extra vote of 5% https://www.steemstem.io/ </h4></center>
<center> <img src="https://cdn.steemitimages.com/DQmPL9pvJA1b7y1iVfTVeHPqR7TX1LidxtRPLVLc5UFXU71/image.png"></center> 

<center> <img src="https://steemitimages.com/0x0/https://cdn.steemitimages.com/DQmRPE1XvcHNHHRD1g5aThwFop2fXAZxrdy198gNH7T86zK/STEEMSTEM-bygtg.gif"><sup>Video credits @gtg</sup></center>

<center> <a href="https://discord.gg/edxs53S">Join the discord channel</a> </center>

<center> <a href="https://steemit.com/~witnesses">Vote for @stem.witness here</a></center>
</div>