__ 57. Selenium is a semiconductor used in photocopying machines. What type of semiconductor would be formed if a small amount of indium impurity is added to pure selenium? 58. The Group 3A/Group 5A semiconductors are composed of equal amounts of atoms from Group 3A and Group 5A-for example, InP and GaAs. These types of semiconductors are used in light -emitting diodes and solid-state : lasers. What would you add to make a p-type semiconductor from pure GaAs? How would you dope pure GaAs to make an n-type semiconductor?

57. When a small amount of indium impurity is added to pure selenium, the resulting semiconductor would be a p-type semiconductor. Indium has fewer valence electrons than selenium, so when it is added as an impurity, it creates holes in the semiconductor lattice. These holes act as positive charge carriers, making the semiconductor p-type.<br /><br />58. To make a p-type semiconductor from pure GaAs, you would add a trivalent impurity such as boron or gallium. These impurities have one less valence electron than arsenic, creating holes in the semiconductor lattice that act as positive charge carriers.<br /><br />To dope pure GaAs to make an n-type semiconductor, you would add a pentavalent impurity such as phosphorus or arsenic. These impurities have one more valence electron than gallium, providing extra electrons that act as negative charge carriers in the semiconductor.