Semiconductor Electronics: Materials, Devices And Simple Circuits

- Get the best out of this chapter by practicing the kind of problems asked in various Exams!
Pattern: Basic questions on classification of materials on the basis of energy bands and the structure of semiconductor materials:
Description: On the basis of overlap or gap between the valence band and conduction band, we are asked to classify the materials as metals, insulators and semiconductors. Questions are also asked regarding the structure of crystal in intrinsic semiconductors and extrinsic (n-type and p-type) semiconductors at the molecular level and how conduction is possible in such semiconductors.
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Pattern: Problems on the concentration or number of charge carriers
Description: Questions are asked about calculating the number of charge carriers. We have to keep in mind that the semiconductor will be electrically neutral and we will apply law of mass action to arrive at the answer.
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Pattern: Basic questions on formation of depletion region, biasing, barrier potential and related terms.
Description: Questions are asked how drift and diffusion lead to the formation of a p-n junction and how a space-charge region on either side of the junction known as depletion region is formed. The barrier potential and the behaviour of the diode under forward/reverse bias is also asked.
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Pattern: Working, circuit diagrams, input and output waveforms of Rectifiers
Description: The property of the p-n junction diodes to allow the flow of current only in one direction (forward bias) is used for rectification of ac voltages. The forward bias resistance is low as compared to the reverse bias resistance. The rectifiers are fed with an input AC supply and they give out rectified DC supply. We are asked to trace the waveforms of input as well as the output. The rectification can be done using half wave or full wave rectifier for which we have to explain the working using neatly labelled circuit diagrams.
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Pattern: Construction, principle, and IV characteristics of optoelectronic junction devices
Description: Semiconductor diodes in which carriers are generated by photons (photo-excitation) are called optoelectronic devices. Questions might be asked on explaining the construction, working principle and their IV characteristics for the following optoelectronic devices:
(i) Photodiodes: used for detecting optical signal (photodetectors).
(ii) Light emitting diodes (LED): convert electrical energy into light.
(iii) Solar cells: Photovoltaic devices which convert optical radiation into electricity.
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Pattern: Writing truth table for a given circuit of logic gates.
Description: We are often asked to write truth table for a circuit consisting of a combination of logic gates. We might be asked to identify the logic operations performed by the circuit in terms of the fundamental gates , i.e. OR, AND, NOT.
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