Which materials form the junction in a typical diode?

• A. N-type and P-type semiconductors
• B. Metals and insulators
• C. Two p-type semiconductors
• D. Two n-type semiconductors

Answer: (A)

A diode’s junction is created by joining a p-type semiconductor with an n-type semiconductor. The p-type side has holes as the majority carriers, while the n-type side has electrons as the majority carriers. When they meet, electrons diffuse into the p-region and recombine with holes on that side, leaving behind charged ions and forming a depletion region that creates a built-in barrier. This barrier controls current flow: it’s easy for forward bias to shrink the barrier and allow current, but reverse bias makes it harder and blocks current. Two regions of the same type (both p-type or both n-type) don’t produce that barrier, so no diode-like junction forms. Metals and insulators don’t give the same semiconductor PN junction that enables the typical diode’s rectifying behavior.