20:T407,Recently, an impact ionization model, which takes the nonlocal nature of the impact ionization process into account, has been described. This model incorporates history-dependent ionization coefficients. Excellent fits to experimental gain and noise measurements for GaAs were achieved using an effective field approach and simple analytical expressions for the ionization probabilities. In the paper, we briefly review the history-dependent model and apply it to Al/sub 0.2/Ga/sub 0.8/As, In/sub 0.52/Al/sub 0.48/As and InP avalanche photodiodes. For the study, the gain and noise characteristics of a series of homojunction avalanche photodiodes with different multiplication thicknesses were measured and fit with the history-dependent model. A "size-effect" in thin (<0.5 /spl mu/m) multiplication regions, which is not adequately characterized by the local-field avalanche theory, was observed for each of these materials. The history-dependent model, on the other hand, achieved close agreement with the experimental results.21:T49f,Avalanche multiplication and excess noise arising from both electron and hole injection have been measured on a series of In _0.52 Al _0.48 As p ⁺ -i-n ⁺ and n ⁺ -i-p ⁺ diodes with nominal avalanche region widths between 0.1 and 2.5 mum. With pure electron injection, low excess noise was measured at values corresponding to effective k=beta/alpha between 0.15 and 0.25 for all widths. Enabled ionization coefficients were deduced using a non-local ionization model utilizing recurrence equation techniques covering an electric field range from approximately 200 kV/cm to 1 MV/cm22:T512,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.23:T4ed,We report avalanche photodiodes fabricated from Al _x In _1-x As _y Sb _1-y wafers grown by molecular beam epitaxy using the digital alloy technique. A

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