Galvanic corrosion effects in InP-based laser ridge structures

Abstract

Galvanic corrosion effects in metallized III-V laser structures have been studied. Small gaps present in the metallization can leave exposed semiconductor regions, which are susceptible to localized corrosion in the presence of an electrolyte. Electochemical measurements in two different electrolytes, i.e., 1% HF and concentrated H3PO4, were made of test structures comprised of n-type InP, p-type InP, and p-type InGaAs, as well as Au. Polarization measurements were made in all cases relative to a Ag/AgCl reference electrode. Corrosion potentials, measured relative to Au, of 540, 180, and 330 mV were obtained for n-type InP, p-type InP, and p-type InGaAs, respectively, in 1% HF. Values of 415, 47, and 138 mV were obtained for n-type InP, p-type InP, and p-type InGaAs, respectively, in concentrated H3PO4. Galvanic current densities of 2.0 × 10−6A/cm2, 1.0 × 10−7 A/cm2, and 4.0 × 10−6 A/cm2 were obtained for galvanic couples of n-type InP/Au, p-type InP/Au, and p-type InGaAs/Au, respectively, in 1%HF. Values of 1.2 × 10−6 A/cm2, 1.2 × 10−7 A/cm2, and 1.0 × 10−6 A/cm2 were obtained for galvanic couples of n-type InP/Au, p-type InP/Au, and p-type InGaAs/Au, respectively, in concentrated H3PO4. Complementary microstructural studies, using scanning electron microscopy, were done on actual metallized ridge laser structures, consisting of a p-type InP ridge with a p-type InGaAs capping layer and a Ti/Pt/Au metallization. Localized pitting of the InGaAs layer was observed for samples with gaps in the metallization.