InAlGaAs alloys grown lattice matched to InP substrates has been shown to be an important material system in fabrication of long-wavelength (1.3-1.55 mu m) photodetectors for fiber-optic applications. We report on the growth of InGaAs/InAlBs p-i-n photodiodes by molecular-beam epitaxy utilizing surface preparation under a solid-source phosphorous flux and an InP buffer layer. Characterization of InGaAs/InAlAs p-i-n photodiodes grown with this technique shows improved direct current and transient device response through the use of a superlattice graded region at the absorption region heterojunction.