We report on the p-type doping of Ga0.51In0.49P lattice matched to GaAs(100) using gaseous diethylzinc by chemical beam epitaxy. The doping concentration was found to decrease with substrate temperature with an apparent activation energy of 5.3 eV. It was found necessary to keep the substrate temperature below about 500-degrees-C to obtain doping in the 10(18)/cm3 range. The doping concentration shows a 0.8th power law with increasing dopant flow rate and saturates at approximately 5 X 10(18)/CM3 . The p-doped GaInP layers were used as cladding layers for 0.98 mum strained InGaAs/GaAs lasers which show state-of-the-art performance.