ONLINE LAB - 10

Name of the experiment: Hall Effect in semiconductors

Objective

The objective of this experiment is to study the behavior of the hall effect in semiconductors from a remote place (online).

Concept of Online Education

Online Education (OE) refers to a mode of education and a system where the interacting learner and the teacher are separated by space where the interaction can be done through high speed internet. It is an alternative method of instructional process to the traditional or conventional method. It enables a large segment of the learners with necessary aptitude to learn more knowledge and professional competence. Since OE is a form if instruction, which is capable of catering for large number of students, it is impossible to deliver the instruction and teaching without the help of a PC and an  internet connection. The easily available internet connectivity is helping to distribute the content and teach the same to the distance learners. This is an effective media and has been extensively used for educational purposes to spread literacy or to give formal and non-formal education all over the world. In the present decade, the online media is dominating in distance education in the developed and developing countries.

In India, continuous efforts are being made to improve the quality and quantity of distance education and several educational commissions have examined and made recommendations for bringing about the required innovations to meet the needs of the distance education system. Moreover, several research studies have indicated that the effective use of new instructional strategies through communication and information technologies, which provide individualized instructions like Learning Module, Programmed Learning Material (PLM) and Computer Based Instructional (CBI) materials. These methods together with its allied communication technologies reach a large number of learners and also help in improving the quality of teaching-learning process in distance education. Now, with the introduction of digital technologies like telecommunication, Interactive television (I-TV) and Virtual conferences (Video conferencing, teleconferencing, audio conferencing and computer conferencing), the virtual learning was established in distance education for teaching, learning and evaluation. In that regard, recently developed online experimentation is playing an important role for online education in India.

Concept of Online Labs

Advancing technology has opened many doors in education. The next step in this direction is interactivity at teaching. Student is able to, not only to see what is involved, but he or she is able to learn from hands on experience. Using computers can be a very effective way of accomplishing this. Students are more motivated and can learn more effectively if they have the opportunity to conduct experiments. Experiments allow a student to compare reality with simulations, collaborate with each other, and give them opportunity to follow their curiosity. Experiments allow a student to compare reality with simulations, collaborate with each other, and give them opportunity to follow their curiosity. Unfortunately, many engineering courses do not include lab component because of significant expense and space considerations. In response to this, I-Lab created remote web accessible laboratories are providing a new framework of science and engineering courses. Remote laboratories allow for much more efficient use of laboratory equipment and give students the opportunity to conduct experiments from the comfort of his home, with an Internet accessible browser. These online Internet accessible labs are important in several learning situations. The first of these is the distance learning scenario. In this situation, learners execute a laboratory oriented course or exercise from their homes or places of employment. Individual learners are remote from each other so that collaboration is distributed. There are currently an increasingly large number of efforts to provide the online analog of the university classroom in various parts of the world. However, there are comparatively few efforts to provide the online analog of the university laboratory, as lectures are much simpler to implement in the Internet environment. However, laboratory learning is a key part of a well designed curriculum. As the number of distance learners and distance learning programs increase, the demand for online laboratory access will also increase. This could for example, also make them available to other national community colleges or partnering Universities and colleges all around the world. So, laboratory based learning experiences that traditionally have been possible only at universities with abundant funds for research are now accessible to many. Third scenario of application is integration of reality into live lectures and seminars. In this situation, teachers present to classroom audience a live (but remote) experiment or demonstration controlled by the instructor. In this scenario, the lab is brought online to the classroom. Economic, space, and cost issues are extremely important and must be considered in setting-up any distance as well as conventional learning environment. Online Laboratories hold promise of being up to three orders of magnitude cheaper to setup than conventional laboratories, requiring less space to run the experiments and being accessible to much larger audience and utilized round the clock.

Typical online Internet accessible laboratory consists of:

v      Lab device, instrument or pilot plant equipment for tele-presence showing the lab to remote users

v      Teleconferencing equipment or at least built-in chatting capabilities for collaboration among students and instructor

v      Control software allowing users to perform experiments, program lab devices and/or run pilot plant.

Introduction to Hall Effect in semiconductors

If a specimen (metal or semiconductor) carrying a current I is placed in a transverse magnetic field B, an electric field ε is induced in the direction perpendicular to both I and B. This phenomenon, known as Hall Effect, is used to determine whether n-type or p-type and to find the carrier concentration. Also, by simultaneously measuring the conductivity σ, the mobility µ can be calculated.

In the figure 1, I is in the positive x direction and B is in the positive z direction, a force will be exerted in the negative y direction on the current carriers. If the semiconductor is n-type, so that current is carried by electrons, these electrons will be forced downward towards side 1 and it becomes negatively charged with respect to side 2. Hence, a potential called V_H, called Hall voltage, appears between the surfaces 1 & 2.

If V_H, B, I are measured, the charge density ρ can be determined from the above eqn. By this we can detect the type of the majority carriers (electrons or holes). If the polarity of V_H is positive at terminal 2, then the carriers must be electrons and ρ = ne, where n is the electron concentration. If, on the other hand, terminal 1 becomes charged positively with respect to terminal 2, the semiconductor must be p- type and ρ = pe, where p is the hole concentration.

It is customary to introduce the Hall coefficient R_H. If conduction is due primarily to charges of one sign, the conductivity σ is related to the mobility µ by σ = ρµ. If the conductivity is measured together with hall coefficient, the mobility can be determined from µ = σR_H. The mobility determined by Hall voltage measurement is called Hall mobility and is higher from the conductivity mobility defined by the mobility of electron and mobility of hole by a factor of 3π/8. This factor arises from the quantum mechanical averaging process.

                                

                                                         Figure 1: - A rectangular Hall sample of an n-type semiconductor

The hall voltage is measurable only in certain materials. In many good conductors, it is not measurable appreciably. It was found that while the direction of hall voltage measured in most substances as shown in figure, it had opposite polarity in germanium at temperatures above 150⁰C. This leads to many investigations in this field in which it was found that while many semiconductors exhibited conventional Hall Effect, there were many others which showed opposite polarity of hall voltage. This can be explained as follows. The direction of magnetic field produced by an electric current is fixed for a given direction of the current, independent of whether it is carried by positive charges moving in the direction of current or by negative charges moving in the opposite direction. Therefore, the direction of mechanical interaction of the external magnetic field with the magnetic field produced by current should be identical in the Hall Effect setups for both germanium and other materials. Consequently, the current streams should get deflected upwards in both the cases. However, the directions of hall voltage are different in the two cases. This will be possible only if the current stream in the second case is constituted by flow of positive charges while that in first case is constituted by flow of negative charges. Therefore, in all the materials in which the direction of the hall voltage was opposite to what was conventionally observed, the current should be carried by some type of mobile positive charges. However, the known theories of matter did not provide for the existence of a mobile positively charged particle in matter. Therefore, the current carriers involved in the  new hall effect experiments were identified as positive ‘holes’ purely on theoretical grounds prior to the observation of the anomalous hall voltage. Thus the first experimental evidence for current conduction by positive holes in a semiconductor was obtained in these “anomalous hall voltage” experiments.

Since the discovery of the anomalous Hall Effect and the subsequent discovery of transistor action, the ‘hole’ has acquired an operational reality and therefore it is often convenient to treat it as though it were an actual positive particle with a definite charge and definite mass. The Hall Effect measurement technique has found wide application in the characterization of semiconductor materials because it gives the resistivity, the carrier density, and the mobility.

 Software(s) and Hardware(s) required

a.       PC with internet connectivity (preferably high-speed)

b.      Teamviewer software for remote user (free downloadable)

Procedure

Step 1 – Read the manual of your experiment from our Homepage link

Step 2 –  Register and Login, remember your “User ID” and “Password”. (Registration is required only for one time)

Step 3 – Read the procedure for doing the experiment and Click on the button to proceed

Step 4 -  Now, “log in” to connect the remote Hardware Setup (at Indian Institute of Technology, Kharagpur, India)

Step 5 - Click on the experiment of your choice (from left column)

Step 6 – Now answer the preliminary quizzes to be eligible for doing the experiment

Step 7 - click on “Book the experiment” to book the particular slot for your experiment (time and date)

Step 8 – Click on “Run Experiment” during your time and slot

 Step 9 – Give the “input parameters” as per requirement of the experiment and click on “enter”

 Step 10 – The output curve will appear on your screen gradually and automatically. The  numerical output data will be shown simultaneously.

 Step 11 – Take the graph and data for showing “Result” using other software

Step 12 - Analyze the data and graph.

Step 13 - To Log out, click on the    and close the window.

Step 14 - Now type www.vit.ac.in/onlinelab to go the home page again.

Step 15 - You are ready for the next experiment.

A typical Hardware Lab setup

Results

The diagrams below shows the quantum Hall Effect and the anomalous Hall Effect.

Conclusion

Hall Effect measurements are not limited to the determination of extrinsic semiconductor type and doping concentration: several other properties of conducting materials, not only in solid state, but also in liquid or plasma conditions, can be detected and measured by this technique, which constitutes a widely used means of research and development.