Physics · Unit 6 · 8 hrs
Semiconductor and Semiconductor devices
Exam-focused notes for Semiconductor and Semiconductor devices (Physics, PHY118): what the TU syllabus asks and how it has actually been tested, with 7 solved past questions from this unit.
What this unit covers
- Intrinsic and extrinsic semiconductors
- Electrical conductivity of semiconductors
- Photoconductivity
- Metal-metal junction: The contact potential
- The semiconductor diode
- Bipolar junction transistor (BJT)
- Field effect transistor (FET)
The semiconductor diode
What do you mean by the contact potential? Give band scheme of a p-n Junction by illustrating: (a) Potential difference V, resulting from the positive donor ions in the n-side of the junction and the negative acceptor ions in the p-side of the depletion layer (b) Potential energy barrier faced by the majority charge carriers (electrons) in the n-side of the diode as they attempt to cross the junction. (c) Potential energy barrier faced by the majority side of the diode as they attempt to cross the junction.[10]
When a p-type and an n-type semiconductor are joined together, diffusion of charge carriers occurs across the junction: - Holes from the p-side diffuse into the n-side - Electrons from the n-side diffuse into the p-side At the junction, recombination takes ...
Full solved answer →Explain equilibrium current across the PN junction? Use Fermi-Dirac statistics and Maxwell-Boltzmann distribution to show the flow n to p is equal to the flow from p to n. How electron current from p to n (that is, associated with minority carries) is not affected by the height of the potential energy barrier? Explain.[10]
At thermal equilibrium (no external bias), a PN junction has a built-in potential barrier (contact potential) V₀ created by the diffusion of majority carriers. Despite this barrier, two opposing currents flow simultaneously and exactly cancel each other, re...
Full solved answer →Electrical conductivity of semiconductors
Derive expression for electrical conductivity of semiconductor in terms of impurity ionization energy. [5]
In an extrinsic semiconductor, impurity atoms (donor or acceptor) are added to a pure semiconductor. These impurity atoms have an ionization energy (also called activation energy) $Ei$, which is the energy required to ionize the impurity atom and release a ...
Full solved answer →Discuss electrical conductivity of semiconductors. Derive expression for conductivity in terms of impurity ionization energy. Give a plot to discuss 'Theoretical temperature dependence of the electrical conductivity of an impurity semiconductor'.[10]
A semiconductor is a material whose valence band and conduction band are partially filled with a small forbidden gap between them. It acts as a conductor at high temperature and as an insulator at low temperature. The temperature coefficient of resistance i...
Full solved answer →Describe electrical conductivity of semiconductors. [5]
A semiconductor is a material whose electrical conductivity lies between that of a conductor and an insulator. Examples include Silicon (Si) and Germanium (Ge). --- From band theory, semiconductors have the following characteristics: - The valence band and ...
Full solved answer →Bipolar junction transistor
Explain the construction and bipolar junction transistor (BJT). [5]
A Bipolar Junction Transistor (BJT) is a three-terminal semiconductor device formed by combining two PN junctions in a specific manner. It is called "bipolar" because its operation involves both types of charge carriers -- holes and electrons. --- A BJT con...
Full solved answer →Explain the construction and working of bipolar junction transistor (BJT). [5]
A Bipolar Junction Transistor (BJT) is a three-terminal device formed by combining two PN junctions in a specific manner. It is called "bipolar" because both holes and electrons participate in conduction. A BJT consists of three doped semiconductor regions ...
Full solved answer →Make Unit 6 stick
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