RF measurement of impact ionization and its temperature dependence in AlSb/InAs HEMTs

The RF characteristics of impact ionization in AlSb/InAs HEMTs were examined by measuring the behavior of S/sub 22/ in the frequency range from 300 kHz to 3 GHz. By varying the drain bias, the onset of impact ionization can be clearly observed. In the ionization region, high gate current, inductive output impedance, current instability with hysteresis, and an increase in low-frequency noise were observed. With decreasing temperature, these effects diminish. The results were compared with measurements made on InAlAs/InGaAs/InP HEMTs. In both transistors, impact ionization as well as deep-level trapping were observed.<>