Nonrectifying junction

In fabricating semiconductor devices, contact between the metal wires and the semiconductor material can create rectifying junctions, also known as Schottky diodes. This is dependent (in the Schottky model) on the difference between the work function of the metal and the electron affinity of the semiconductor. In some cases the contact is a Schottky diode, in others the contact is ohmic, that is to say the voltage drop is proportional to the bias. But in practical, the metal–semiconductor interfaces do not follow exactly the Schottky model, and the presence of states at the interface (oxide, defects, etc.) can make the behavior of the junction almost independent of the difference of work function/electron affinity. But in fact, when designing a device, to be sure of an ohmic contact, the designer will choose the doping of the contact region according to the type of contact wanted (usually n+ doped contact for a n-type silicon wafer and aluminum wires).