We present a systematic study of avalanche multiplication and excess noise characteristics of InAlAs on a series of p+-i-n + and n+-i-p+ diodes with nominal intrinsic region widths from 0.1mum to 2.5mum. The carrier threshold energies and the ionization coefficient for enabled carriers between electric fields of 220 ky/cm to 980 ky/cm are extracted by fitting to the measured electron- and hole-initiated multiplication and excess noise characteristics by using the coupled integral equations technique.