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A new planar InP/InGaAsP avalanche photodiode, which is fabricated by Be+implantation through a dish-shaped InGaAs mask, has been developed. A three-dimensional graded junction is obtained and a uniform gain as high as 30 achieved without edge or surface breakdown. The dish-shaped InGaAs implantation mask is formed by a photoelectrochemical etching technique. Device modeling indicates that the graded junction and low doping concentration can prevent edge breakdown and greatly suppress the surface field. The diode has a separated absorption and multiplication structure grown by hydride vapor-phase epitaxy. These devices exhibit low primary dark currents (≈ 1 nA), and high quantum efficiencies close to that of an InGaAs p-i-n at 1.3-µm wavelength. Sensitivity measurements at bit rates of 1.7 Gbit/s give a minimum average receiver power required for 10-9BER of -35.5 dBm.