Noun
English Wikipedia has an article on:heterojunctionWikipedia
heterojunction (plural heterojunctions)
(electronics) Any junction between two different semiconductors; functions as a diode
A mnemonic device for the PNP transistor symbol is "pointing in (proudly/permanently)", based on the arrows in the symbol and the letters in the name. citation Heterojunction bipolar transistor Bands in graded heterojunction NPN bipolar transistor. Source: Internet