Elastic Stresses in InGaAsP Heterostructures with Alloyed Contact Metallizations

Abstract

ABSTRACTWe have measured the radius of curvature of InGaAsP/InP heterostruc-ture wafers grown by liquid phase epitaxy, after growth and after broad area p-and n-metallizations used in the fabrication of 1.3vm lasers, by the x-ray automatic Bragg angle control technique. The heterostructure consisted of an n-InP buffer layer (0.2μm), an InGaAsP active layer (0.3 – 0.4μm), a p-InP layer (0.7μm) and either a p-InGaAsP or a p-InGaAs cap layer (0.6 – 0.7μm) grown on a 250 μm thick n-Inp substrate. The radius of curvature measured after growth was found to be in good agreement with the value calculated using the lattice mismatch strains. The changes in the radius of curvature after deposition and alloying of a 1000 Å thick AuZnAu p-metallization and after thinning the substrate to 86μu followed by 2900 Å thick alloyed GeAu n-metallization are such that the metal films are under a tensile strain. The value of the strain is calculated to be 8 × 10-3 and 1.6 × 10-3 respectively for the p- and n-metals. The radius of curvature was measured after the final metallization and annealing of 2500 A thick TiPt layer on the p-side. The annealed TiPt layer was found to have a compressive strain of 6 × 10-3. The stress in the active layer remained tensile at all times for both wafers and it was in the range 9 × 10 – 1.4 × 10 dyne cm-2. These values are less than the estimated fracture stress of InGaAsP by an order of magnitude.