Substrate preparation and interface grading in InGaAs InAlAs photodiodes grown on InP by molecular-beam epitaxy

InAlGaAs alloys grown lattice matched to InP substrates has been shown to b e 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 surf ace preparation under a solid-source phosphorous flux and an InP buffer lay er. Characterization of InGaAs/InAlAs p-i-n photodiodes grown with this tec hnique shows improved direct current and transient device response through the use of a superlattice graded region at the absorption region heterojunc tion. (C) 1999 American Vacuum Society. [S0734-211X(99)00403-5].