On the low-temperature degradation of (AlGa)As/GaAs modulation-doped field-effect transistors

A comprehensive study of the anomalous low-temperature behavior of modulation,doped (Al, Ga)As/GaAs field-effect transistors is reported, Experiments on the effect of bias stress on the current-voltage characteristics in lateral resistors, 1-µm gate FET\´s, and a novel dual-gate tester are presented along with the results of freeze-out, optical spectroscopy, and trapping kinetics experiments. Both modulation-doped (Al, Ga)As/GaAs heterostructures and isolated (Al, Ga)As layers are examined. The results delineate the conditions under which threshold shift and collapse occur. Based on these results a detailed physical model which explains these effects is proposed. One important conclusion of this work is that the collapse is not related to hot electron injection from the high mobility channel, as suggested earlier, but is a property of a highly doped AlGaAs layer under bias.