A systematic study of avalanche multiplication on a series of In0.52Al0.48As p(+)-i-n(+) and n(+)-i-p(+) diodes with nominal intrinsic region thicknesses ranging from 0.1 to 2.5 mu m has been used to deduce effective ionization coefficients between 220 and 980 kV (.) cm(-1). The electron and hole ionization coefficient ratio varies from 32.6 to 1.2 with increasing field. Tunneling begins to dominate the bulk current prior to avalanche breakdown in the 0.1-mu m-thick structure, imposing an upper limit to the operating field. While the local model can accurately predict the breakdown in the diodes, multiplication is overestimated at low fields. The effects of ionization dead space, which becomes more significant as the intrinsic region thickness reduces, can be corrected for by using a simple correction technique.