Gallium contamination of InP epitaxial layers in InP/InGaAsP multilayer structures grown by hydride transport vapor phase epitaxy

Gallium contamination of InP epitaxial layers grown in CVD reactors designed for InGaAsP/InP multilayer structures was observed by secondary ion mass spectrometry (SIMS). Defect characterization of gallium-contaminated InP buffer layers by the damage-free grooving and etching technique showed misfit dislocations and an interfacial layer containing a high density of saucer pits. Cross-sectional transmission cathodoluminescence further indicated that these defects are nonradiative recombination centers. Results from x-ray double-crystal diffractometry o a successively chemically stripped InP buffer layer indicated that the misfit was confined to the region near the interfacial layer which was consistent with the SIMS profile where the gallium content peaked near the interfacial layer. By presaturating the reactor with PH3, the amount of the gallium which was incorporated into the InP was found to be reduced. SIMS profiles of gallium on layers grown after the withdrawal of the gallium source from th reactor indicated that the indium melt was cross contaminated even though the reactor was designed to physically exclude the gallium source from the indium source. Small amounts of As, Fe, Si, Cr, and Zn were also found. The possible mechanisms which lead to the cross contamination are discussed. The evidence seems to support the suggestion that Ga is incorporated preferentially in the growth of ternary and quaternary compounds. In a four-layer laser structure consisting of n-InP(buffer)/InGaAsP(active)/p-InP(cap)/p -InGaAsP(contact) layers, both gallium and arsenic contamination were observed in p-InP and n-InP regions by Auger spectroscopy.