Theoretical calculations predict1 and experiments confirm2,3 that the highest lightwave receiver sensitivities are achieved with avalanche photodiodes (APDs) in the front end. The evolution of lightwave transmission systems toward multigigabit data rates has stimulated research on wide-bandwidth APDs. To date the SAGM-APD structure has shown the most promise for high-frequency operation.4,5 It consists of an InP multiplication region and an ln0.53Ga0.47As absorption layer separated by a thin transition region to minimize hole trapping at the heterojunction interfaces. Optimization of this structure to obtain wide bandwidths without sacrificing performance in other areas, such as dark current, gain, or quantum efficiency, severely constrains the wafer parameters. The resulting narrow tolerances in the thicknesses and carrier concentrations of the constituent regions are more difficult to satisfy by liquid-phase epitaxy (LPE) than by vapor-phase growth techniques. We report on backilluminated mesa-structure InP/InGaAsP/InGaAs APDs (Fig. 1) grown by chemical beam epitaxy, a growth technique that combines many of the advantages of molecular beam epitaxy and metal-organic chemical vapor deposition.
© 1988 Optical Society of AmericaPDF Article