Basics of n-type semiconductors – charge neutrality and doping examples Which statement correctly describes n-type semiconductors and their formation by impurity addition?

Introduction / Context:
Doping semiconductors with specific impurities changes the majority carrier type and conductivity. Distinguishing n-type from p-type, and recognizing common dopants, is foundational for designing diodes, BJTs, MOSFETs, and integrated circuits.

Given Data / Assumptions:

• Silicon (group IV) can be doped with group V donors or group III acceptors.
• Charge neutrality refers to the overall crystal, not to local charge states.
• Common dopants: phosphorus, arsenic, antimony (donors, n-type); boron, aluminum, gallium, indium (acceptors, p-type).

Concept / Approach:

Adding a group V element like phosphorus to silicon introduces an extra valence electron. This donor electron is weakly bound and easily thermally ionized, contributing free electrons to the conduction band. The result is an n-type semiconductor with electrons as majority carriers, yet the bulk crystal remains electrically neutral due to ionized donor cores balancing electron charge.

Step-by-Step Solution:

Verification / Alternative check:

Energy-band diagrams show donor levels just below the conduction band in n-type Si, enabling easy electron excitation at room temperature and higher conductivity than intrinsic Si.

Why Other Options Are Wrong:

Option A: n-type is not net negatively charged. Option B: indium (group III) creates p-type in Ge. Option E: boron in Si creates p-type, not n-type. Option D is therefore false.

Common Pitfalls:

Confusing majority carrier type with overall charge; misremembering which periodic table groups produce donors versus acceptors.

Final Answer:

are produced when phosphorus is added to silicon