Mind The Semiconductor Gap

Behold! The unholy matrimony of semiconductor physics and British transit warnings! This meme takes the p-n junction (the fundamental building block of electronic devices) and slaps a London Underground "Mind the Gap" sign on it. The gap refers to the depletion region between p-type and n-type semiconductors where electrons and holes dare not tread. Meanwhile, Officer Buzzkill is trying to stop electrons from jumping the forbidden energy gap between valence and conduction bands. It's basically semiconductor police brutality! Your professor clearly had a thing for combining quantum mechanics with public transportation safety. Truly the work of a deranged genius!