NOVEL METAL-SEMICONDUCTOR-METAL PHOTODETECTORS ON BULK SEMIINSULATINGINDIUM-PHOSPHIDE

Depositing Pd or Au on InP at substrate temperatures near 77 K (LT) ha s previously been found to significantly reduce the interaction betwee n the metal and semiconductor upon formation of the interface. In this letter, this technique was used to fabricate metal-semiconductor-meta l photodetectors (MSMPD's) on semi-insulating (SI) InP substrates with superior characteristics compared to detectors formed using standard room temperature (RT) metal deposition. Detectors having a LT-Pd-SI-In P structure had a dark current of 80 nA at 5 V, which was a factor of 4 lower than the dark current of conventional MSMPD's. Additionally, L T-Pd-SI-InP MSMPD's exhibited excellent saturation characteristics and a responsivity of 0.75 A/W. Detectors with an indium-tin-oxide (ITO)- LT-Au (200 Angstrom)-SI-InP structure had a higher responsivity of 1.0 A/W, due to the relative transparency of this metallization. In contr ast, MSMPD's with RT metallizations had poor saturation characteristic s, consistent with the results of others. The difference in the illumi nated characteristics of MSMPD's with RT and LT metallizations was due to a change in the internal photoconductive gain mechanism. In RT det ectors, hole trapping at interface states Dear the cathode dominated t he gain mechanism. In LT detectors, the difference in carrier transit- times dominated.