On the temperature dependence of the impact ionization in HFET and the corresponding RF- and noise performance

Extremely high cut-off frequencies with excellent noise performance demonstrate the capability of heterostructure field-effect transistors (HFET) based on the InAlAs/InGaAs/InP material system for microwave communication systems and for opto-electronic applications. But, due to the low energy band-gap of the channel material, at high drain-source-voltages V/sub DS/ impact ionization in the channel influences the DC- and especially the RF- and noise properties. We present temperature dependent on-wafer characterization of the DC, the high frequency (45 MHz up to 40 GHz) and noise behaviour (2 GHz up to 18 GHz) of InP-based HFETs. These results are the basis for the discussion of the temperature dependence of impact ionization in HFET. Furthermore, an extended small-signal equivalent circuit is given, which is correlated to the physical interpretation of impact ionization process in HFET.