Multiplication characteristics of thin Al/sub x/Ga/sub 1-x/As(x=0 to 0.3) diodes

In this work, we describe the measured electron and hole multiplication characteristics for Al/sub .15/Ga/sub .85/As and Al/sub .3/Ga/sub .7/As homojunction p-i-n diodes with i-region thicknesses from 1/spl mu/m down to 0.025/spl mu/m. When the conventional local model of ionisation is employed to deduce electron and hole ionisation coefficients, /spl alpha/ and /spl beta/, the results from the 1/spl mu/m and 0.5/spl mu/m structures of all compositions agree with previously published bulk data. However, deviations from this behaviour are seen for the thinner structures. For the O.1/spl mu/m case, /spl alpha/ lies below the bulk data at low fields but converges when the field is increased. For the 0.05/spl mu/m and 0.025/spl mu/m structures, this departure becomes even more significant with higher fields required to initiate measurable multiplication but /spl alpha/ increasing rapidly with field. The effective ionisation coefficients are seen to decrease with increasing aluminium composition at low fields, as expected due to the larger band-gap and higher scattering rates, but converge at higher fields. This behaviour results in an apparent convergence of breakdown voltages for the different compositions as the device thickness is reduced.