MICROSTRUCTURAL STUDY OF AU-PD-ZN OHMIC CONTACTS TO P-TYPE INGAASP-INP

A detailed microstructural study has been done on Au-Pd-Zn ohmic conta cts to p-type InGaAsP epitaxially grown on InP. The doping level in th e InGaAsP was 1.0 x 10(19) to 1.5 x 10(19) cm(-3) near the surface wit h the Zn concentration graded to a value of 7 x 10(18) cm(-3) at the I nGaAsP-InP interface. Metal layers (10 nm Pd, 3 nm Zn, 25 nm Pd and 50 nm Au) were deposited sequentially by electron beam evaporation. Cont act resistances less than approximate to 10(-4) Omega cm(2) were achie ved for all annealing temperatures studied (380-440 degrees C) and a m inimum contact resistance of approximate to 2 x 10(-6) Omega cm(2) was obtained for an anneal at 400 degrees C for 20 s. Comparisons were ma de to similar metallizations on p-type InP. Lower contact resistances were achieved for the quaternary material compared with the binary mat erial, however, contact stability and uniformity were worse.