MetallSemiconductor

MetallSemiconductor, usually written as a metal–semiconductor junction, refers to the interface where a metal electrode meets a semiconductor material. These junctions govern the flow of charge across the boundary and are essential components of many electronic devices, from diodes to transistors. The interaction at the interface depends on the relative work functions, doping, and interfacial chemistry, which determine the extent of charge transfer and band bending in the semiconductor.

Two principal classes are diodes created by Schottky (rectifying) contacts and ohmic contacts. A Schottky junction forms a barrier that controls carrier injection and exhibits rectifying current–voltage behavior. Ohmic contacts aim to minimize barrier height to allow near-linear current flow regardless of polarity. The exact barrier height and contact resistance are influenced by interfacial states, defects, and Fermi level pinning, as well as by semiconductor doping and metal choice.

Common semiconductors include silicon, germanium, GaAs, InP, silicon carbide, and gallium nitride. Metals often used are aluminum, titanium, nickel, gold, and platinum. Fabrication typically involves surface cleaning and metal deposition by evaporative or sputtering techniques, sometimes followed by alloying, annealing, or diffusion to tailor the interface.

Applications span Schottky diodes, sensors, and active devices such as MESFETs and HEMTs, where metal gates or contacts form part of the device structure. Challenges include interface states causing Fermi level pinning, contact resistance at nanoscale dimensions, and thermal stability under operation.