The present invention relates broadly to epitaxial layer diodes, and in particular to an ultraviolet light emitting diode array in aluminum nitride on a sapphire base.
In the prior art, semiconductor circuits usually utilized as a base a slice of single crystal silicon, more or less circular, about 2 in. in diameter, and a fraction of an inch thick. Typically, this material is doped with p-type impurities. A film of semiconductor, less than 1/1000 in. thick, is then grown upon this substrate in a vapor-phase reaction of a silicon-containing compound. The conditions of this reaction are such that the film maintains the single-crystal nature of the substrate. Such films are called epitaxial. By incorporating n-type impurities into the gas from which the film is grown, the resulting epitaxial film is made n-type.
The silicon slice is then placed into an oxygen atmosphere at high temperatures (1200.degree. C). The silicon and oxygen react, forming a cohesive silicon dioxide film upon the surface of the slice that is relatively impervious in the electrically active impurities.
To form the particular semiconductor regions required in the fabrication of electronic devices, however, p and n-type impurities must be introduced into certain regions of the semiconductor. In the planar technology, this is done by opening windows in the protective oxide layer by photoengraving techniques, and then exposing the slice to a gas containing the appropriate doping impuritiy. In the case of an integrated circuit, the isolation regions -- p-type regions which, together with the p-type substrate, surround the separate pockets of the n-type film -- are formed first by the diffusion of a p-type impurity. This is followed by a shorter exposure to p-type impurities during which the base region of the transistors and the resistors are formed. This procedure is repeated until the desired elements and a particular circuit configuration is finally established.