What characterizes n-type semiconductors?

n-type semiconductors are characterized by an abundance of electrons, which arise when donor impurities are added to a pure semiconductor material, such as silicon. In this case, the donor impurities typically possess extra valence electrons compared to the host semiconductor atoms. When these impurities are introduced, they provide additional negatively charged electrons to the conduction band of the semiconductor, which increases its conductivity as these extra electrons are free to move and carry charge.

In contrast, the presence of excess holes is characteristic of p-type semiconductors, where acceptor impurities are added, creating positively charged vacancies. The other option mentioning the addition of acceptor impurities pertains to p-type materials specifically, not n-type. The statement regarding thermal conductivity is less relevant to the fundamental defining characteristics of n-type semiconductors. Thus, an abundance of electrons directly links to the defining properties of n-type semiconductors, making this the correct characterization.