Low multiplication noise thin Al/sub 0.6/Ga/sub 0.4/As avalanche photodiodes

Abstract

Avalanche multiplication and excess noise were measured on a series of Al/sub 0.6/Ga/sub 0.4/As p/sup +/in/sup +/ and n/sup +/ip/sup +/ diodes, with avalanche region thickness, w ranging from 0.026 /spl mu/m to 0.85 /spl mu/m. The results show that the ionization coefficient for electrons is slightly higher than for holes in thick, bulk material. At fixed multiplication values the excess noise factor was found to decrease with decreasing w, irrespective of injected carrier type. Owing to the wide Al/sub 0.6/Ga/sub 0.4/As bandgap extremely thin devices can sustain very high electric fields, giving rise to very low excess noise factors, of around F/spl sim/3.3 at a multiplication factor of M/spl sim/15.5 in the structure with w=0.026 /spl mu/m. This is the lowest reported excess noise at this value of multiplication for devices grown on GaAs substrates. Recursion equation modeling, using both a hard threshold dead space model and one which incorporates the detailed history of the ionizing carriers, is used to model the nonlocal nature of impact ionization giving rise to the reduction in excess noise with decreasing w. Although the hard threshold dead space model could reproduce qualitatively the experimental results, better agreement was obtained from the history-dependent model.