91Ó°ÊÓ

What is the distinction between electronic and ionic conduction?

In terms of electron energy band structure, discuss reasons for the difference in electrical conductivity between metals, semiconductors, and insulators

At room temperature the electrical conductivity and the electron mobility for aluminum are \(3.8 \times 10^{7}(\Omega-\mathrm{m})^{-1}\) and \(0.0012 \mathrm{m}^{2} / \mathrm{V}-\mathrm{s}, \mathrm{re}\) spectively. (a) Compute the number of free electrons per cubic meter for aluminum at room temperature. (b) What is the number of free clectrons per aluminum atom? Assume a density of \(2.7 \mathrm{g} / \mathrm{cm}^{3}\)

(a) Calculate the number of free electrons per cubic meter for silver, assuming that there are 1.3 free electrons per silver atom. The electrical conductivity and density for Ag are \(6.8 \times 10^{7}(\Omega-\mathrm{m})^{-1}\) and \(10.5 \mathrm{g} / \mathrm{cm}^{3}, \mathrm{re}\) spectively. (b) Now compute the electron mobility for Ag.

Tin bronze has a composition of 89 wt \(\%\) Cu and 11 wt \(\%\) 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:

At room temperature the electrical conductivity of \(\mathrm{PbS}\) is \(25(\Omega-\mathrm{m})^{-1}\), whereas the electron and hole mobilities are 0.06 and \(0.02 \mathrm{m}^{2} / \mathrm{V}-\mathrm{s},\) respectively. Compute the in trinsic carrier concentration for PbS at room temperature.

Is it possible for compound semiconductors to exhibit intrinsic behavior? Explain your answer.

An \(n\) -type semiconductor is known to have an electron concentration of \(5 \times 10^{17} \mathrm{m}^{-3}\). If the electron drift velocity is \(350 \mathrm{m} / \mathrm{s}\) in an electric field of \(1000 \mathrm{V} / \mathrm{m}\), calculate the conductivity of this material

(a) In your own words, explain how donor impurities in semiconductors give rise to free electrons in numbers in excess of those generated by valence band-conduction band excitations. (b) Also explain how acceptor impurities give rise to holes in numbers in excess of those generated by valence bandconduction band excitations.

(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.