Question Video: Recognizing Pentavalent Impurities as Donor Atoms Which Produce n-Type Semiconductors Physics • Third Year of Secondary School

Video Transcript

Fill in the blank. Adding pentavalent atoms to a pure semiconductor changes it to blank. (A) An intrinsic semiconductor, (B) a superconductor, (C) a p-type semiconductor, (D) an n-type semiconductor.

Let’s begin by recalling some basic information and vocabulary regarding semiconductors. In this question, we’re talking about starting with a pure semiconductor. Recall that pure semiconductors are composed of one type of element and have an equal number of free electrons and vacancies. We should also recall that pure semiconductors are also called intrinsic semiconductors. Further, we’ve been asked about the effects of taking a pure semiconductor and adding a certain kind of atom to it. This process is called doping. And the effects of doping depend on what type of dopant, or impurity atom, is used. Depending on the type of impurity added to the semiconductor, we end up with either a p-type or n-type semiconductor.

We should recall that p-type semiconductors have a greater number of vacancies, or electron holes, than free electrons. To get a p-type semiconductor, we must use trivalent dopant atoms, which have three electrons in the outermost electron shell. On the other hand, n-type semiconductors have a greater number of free electrons than vacancies. To get an n-type semiconductor, we must use pentavalent dopant atoms, which have five outermost electrons.

Remember that this question is asking about doping a pure semiconductor with pentavalent atoms, so it looks like (D) is the best answer. Answer choice (A) suggests that doping with pentavalent atoms creates an intrinsic semiconductor. This can’t be true, since intrinsic semiconductor is just another name for pure semiconductor. And we know that once we dope a semiconductor, it’s no longer pure. Therefore, we should eliminate answer choice (A).

Next, option (B) says superconductor, which is another class of material altogether. A superconductor is not a type of semiconductor. And so we know that this is wrong as well. For option (C), we’ve already established that p-type semiconductors must have been doped with trivalent impurities, not pentavalent. So let’s also eliminate this option. This leaves us with option (D), which is the correct answer. Adding pentavalent atoms to a pure semiconductor changes it to an n-type semiconductor.