Bilayer electrode on a n-type semiconductor

DETAILED DESCRIPTION It is an object of the present invention to provide a contact to n-type semiconductors with a low barrier height.
This object is achieved by a bilayer electrode in contact with a n-type semiconductor, comprising: a) a thin non-conducting layer contacting the n-type semiconductor, the layer having a strong dipole character such as alkali or alkaline earth metal fluorides or oxides; b) a conductive layer contacting the non-conducting layer, the layer having a good stability against atmospheric oxidation; and c) the thickness of the non-conducting layer being selected so that the bilayer forms a contact with a low barrier height, the bilayer providing stability against atmospheric corrosion.
ADVANTAGES OF THE INVENTION Metals with a low work function such as lithium, sodium, potassium, rubidium, and cesium is an ideal candidate to form low-resistance contacts to n-type semiconductors.
However, they are extremely sensitive to oxidation and show poor corrosion resistance.
In contrast, alkali or alkaline earth metal fluorides or oxides are quite stable, and the reaction with most of the materials is thermodynamically inhibited.
Alkali and alkaline earth metal fluorides or oxides are insulating.
For instance, lithium fluoride is a superior insulating material because it has the highest bandgap energy of 12 eV among oxides and fluorides.
It is disclosed in this invention, however, that lithium fluoride in the form of ultra thin film (tens of angstroms) backed by a suitable metal layer is an effective electron injector for organic electroluminescent devices.