P-I-N PHOTODIODES WITH TRANSPARENT CONDUCTIVE CONTACTS

This invention pertains to a p-i-n In0.53Ga0.47As photodiode having an optically transparent composite top electrode consisting of a thin semitransparent metal layer (24) from 10 to 40 nm thick and a transparent cadmium tin oxide (CTO) layer (25) from 90 to 600 nm thick. The metal layer makes a non-alloyed ohmic contact to the semiconductor surface, acts as a barrier between the semiconductor and the CTO preventing oxidation of the semiconductor from the O2 in the plasma during reactive magnetron sputtering of the CTO layer, and prevents formation of a p-n junction between the semiconductor and CTO. The CTO functions as the n or p contact, an optical window and an anti-reflection coating. The top electrode also avoids shadowing of the active layer by the top electrode, thus allowing greater collection of incident light. Since the top electrode is non-alloyed, inter-diffusion into the i-region is not relevant, which avoids an increased dark current.