Low excess noise in avalanche photodetectors (APDs) is desired for improved sensitivity and high-frequency performance. Gain and noise characteristics are measured for InAlAsp-i-nhomojunction APDs that were grown with varyingi-region widths on InP by molecular beam epitaxy. The effective ionization ratiok (&bgr;/&agr;)determined by noise measurements shows a dependence on multiplication region width, reducing from 0.31 to 0.18 for multiplication region thicknesses of 1600–200 nm. This trend follows previously shown results in AlGaAs-based APDs, which exhibit reduced excess noise due to nonlocal multiplication effects. These results show that this effect is a characteristic of thin avalanche regions and is not a material-specific phenomenon. ©1998 American Institute of Physics.