Low multiplication noise thin Al0.6Ga0.4As avalanche photodiodes

Avalanche multiplication and excess noise were measured on a series of Al0. 6Ga0.4As p(+)in(+) and n(+)ip(+) diodes, with avalanche region thickness, z u ranging from 0.026 mum to 0.85 mum. 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 omega, irrespective of injected carrier type, O wing to the wide Al0.6Ga0.4As bandgap extremely thin devices can sustain ve ry high electric fields, giving rise to very low excess noise factors, of a round F similar to3.3 at a multiplication factor of M similar to 15.5 in th e structure with omega = 0.026 mum, This is the lowest reported excess nois e at this value of multiplication for devices grown on GaAs substrates. Rec ursion equation modeling, using both a hard threshold dead space model and one which incorporates the detailed history of the ionizing carriers, is us ed to model the nonlocal nature of impact ionization giving rise to the red uction in excess noise with decreasing w, Although the hard threshold dead space model could reproduce qualitatively the experimental results better a greement was obtained from the history-dependent model, p.