Magnetoresistance method to determine GaAs and AlxGa1−xAs mobilities in AlxGa1−xAs/GaAs modulation-doped field-effect transistor structures

Abstract

Charge carrier mobilities are conveniently measured in simple, homostructure field-effect transistors (FET’s) by means of the geometric magnetoresistance (GMR) technique. Heterostructure FET’s, however, are more complicated because of multiple conducting regions, as well as multiple conducting bands within a given region. We apply a multilayer GMR mobility model to a frequently used heterostructure FET design, namely, the Al0.3Ga0.7As/GaAs modulation-doped FET (MODFET). By analyzing the results at different magnetic fields, we can separate the contributions of the various GaAs subbands and the Al0.3Ga0.7As conduction band. In the particular MODFET structure studied here, the lowest GaAs subband mobility ranges from 5.7×103 cm2/Vs at threshold to 6.9×103 cm2/Vs at saturation, while the Al0.3Ga0.7As mobility is about 5×102 cm2/Vs. This is the first time that the various mobilities in MODFET structures have been separately measured.