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Chapter 18: Problem 27

(a) Explain why no hole is generated by the electron excitation involving a donor impurity atom. (b) Explain why no free electron is generated by the electron excitation involving an acceptor impurity atom.

Short Answer

Expert verified
Answer: No hole is generated during the electron excitation process involved with a donor impurity atom because the excitation process does not leave a vacancy in the valence band; instead, the donor site stays positively charged. No free electron is generated during the electron excitation process involved with an acceptor impurity atom because the electron is not excited to the conduction band; instead, the electron fills a vacancy in the valence band created by the acceptor impurity, and the acceptor site becomes negatively charged.

Step by step solution

01

Understand the Impurity Atoms

Donor impurity atoms are atoms that have an extra valence electron compared to the atoms of a semiconductor crystal. They can donate this extra electron to the crystal lattice. Acceptor impurity atoms, on the other hand, have one less valence electron and can accept an electron from the semiconductor crystal.
02

Analyze Donor Impurity Atoms and Electron Excitation

In the case of a donor impurity atom, it donates an extra electron to the conduction band. When the electron is excited from the donor impurity level to the conduction band, there is no vacancy created in the valance band. Instead, the donor site is left positively charged because it has lost an electron, but no hole is created in the valence band.
03

Answer for Part (a)

Therefore, for part (a) of the exercise, no hole is generated by the electron excitation involving a donor impurity atom because the excitation process does not leave a vacancy in the valence band. Instead, the donor site stays positively charged.
04

Analyze Acceptor Impurity Atoms and Electron Excitation

In the case of an acceptor impurity atom, it accepts an electron from the valence band to complete its outer electron shell. This process creates a hole in the valence band. When an electron from the valence band fills the hole created, the acceptor site becomes negatively charged.
05

Answer for Part (b)

For part (b) of the exercise, no free electron is generated by the electron excitation involving an acceptor impurity atom because the electron is not excited to the conduction band. Instead, the electron fills a vacancy in the valence band created by the acceptor impurity, and the acceptor site becomes negatively charged.

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Most popular questions from this chapter

For each of the following pairs of semiconductors, decide which will have the smaller band gap energy, \(E_{g}\), and then cite the reason for your choice. (a) \(\mathrm{ZnS}\) and \(\mathrm{CdSe}\), (b) \(\mathrm{Si}\) and \(\mathrm{C}\) (diamond), (c) \(\mathrm{Al}_{2} \mathrm{O}_{3}\) and \(\mathrm{ZnTe}\), (d) InSb and ZnSe, and (e) GaAs and AlP.

Will each of the following elements act as a donor or an acceptor when added to the indicated semiconducting material? Assume that the impurity elements are substitutional. \begin{tabular}{ll} \hline Impurity & Semiconductor \\ \hline \(\mathrm{P}\) & \(\mathrm{Ge}\) \\ \(\mathrm{S}\) & \(\mathrm{AIP}\) \\ \(\mathrm{In}\) & \(\mathrm{CdTe}\) \\ \(\mathrm{Al}\) & \(\mathrm{Si}\) \\ \(\mathrm{Cd}\) & \(\mathrm{GaAs}\) \\ \(\mathrm{Sb}\) & \(\mathrm{ZnSe}\) \\ \hline \end{tabular}

Briefly describe electron and hole motions in a \(p-n\) junction for forward and reverse biases; then explain how these lead to rectification.

(a) Using the data in Figure \(18.8\), determine the values of \(\rho_{0}\) and \(a\) from Equation \(18.10\) for pure copper. Take the temperature \(T\) to be in degrees Celsius. (b) Determine the value of \(A\) in Equation \(18.11\) for nickel as an impurity in copper, using the data in Figure \(18.8\). (c) Using the results of parts (a) and (b), estimate the electrical resistivity of copper containing \(1.75\) at \(\%\) Ni at \(100^{\circ} \mathrm{C}\).

Tin bronze has a composition of \(92 \mathrm{wt} \% \mathrm{Cu}\) and \(8 \mathrm{wt} \% \mathrm{Sn}\), and consists of two phases at room temperature: an \(\alpha\) phase, which is copper containing a very small amount of tin in solid solution, and an \(\epsilon\) phase, which consists of approximately 37 wt \(\%\) Sn. Compute the room temperature conductivity of this alloy given the following data: \begin{tabular}{ccc} \hline \multicolumn{2}{c}{ Electrical } \\ Phase & Resistivity \((\Omega \cdot m)\) & Density \(\left(g / c m^{5}\right)\) \\\ \hline\(\alpha\) & \(1.88 \times 10^{-8}\) & \(8.94\) \\ \(\epsilon\) & \(5.32 \times 10^{-7}\) & \(8.25\) \\ \hline \end{tabular}
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