A physically unclonable function (PUF) device 1 capable of exhibiting a unique quantum mechanical effect as a result of quantum mechanical confinement exhibited by the device 1. The device 1 comprises a group IV semiconductor heterostructure. The group IV semiconductor heterostructure may comprise Silicon/Germanium. The device 1 may comprise a group IV semiconductor resonant tunnelling diode (RTD).A Si-integrated circuit, method, use, and apparatus are also provided.