Abstract
We present d.c. and r.f. measurements in AlInAs/GaInAs/InP high electron mobility transistors with different gate length. First we observed a kink effect in the I-V characteristics. Next we have extracted the different parameters of the r.f. equivalent circuit from scattering parameters. Finally we have deduced the current spectral density and time constants from the noise measurements. These results confirm the presence of an excess noise contribution related to impact ionization in the channel, which affects low noise application seven at microwave frequencies.