Low Temperature Instabilities in AlGaAs/InGaAs Pseudomorphic HEMT’s Induced by Trapping/Detrapping Effects

We report on the behaviour of the current-voltage characteristics of AlGaAs/InGaAs pseudomorphic-HEMT's biased at room and low temperature (${\rm -180^\circ C}$) for a variety of bias voltages. A noticeable decrease in the absolute value of the threshold voltage ${\rm \mid V_P \mid}$ takes place, causing a remarkable collapse of the output drain current ${\rm I_{ds}}$ for low drain to source bias voltage ( ${\rm V_{ds}}$ around 1.5 V). We attribute this collapse to electron trapping under the gate. When ${\rm V_{ds}}$ increases over 2 V a reduction in the collapse of the output characteristics is observed as a consequence of the decrease in the trapped negative charge occuring at high ${\rm V_{ds}}$ due to compensation by holes generated by impact-ionization.