Interface states of modulation-doped AlGaAs/GaAs heterostructures

We have used the admittance spectroscopy to investigate interface states associated with heterojunction of modulation-doped AlGaAs/GaAs FET's. Anomalous frequency dispersion of the capacitance was observed. The results of the measurements were interpreted in terms of an equivalent circuit containing a series resistance of the two-dimensional electron gas in the ungated region between the gate and the source and drain electrodes. The maximum density of the interface states was found to be 1.3 × 10
¹²
cm
^-2
. eV
^-1
around 0.13 eV below the E
c
edge of GaAs.