CHARGE TRAPPING IN GaAs/AlGaAs MODULATION DOPED FETs.

Charge trapping at low temperature which has been linked to the D-X center in n-type AlGaAs has been identified as a major problem in GaAs/n-AlGaAs selectively doped FETs. We report measurements of the pinch-off voltage shift due to charge trapping and find that our data can be interpreted by assuming a distribution of capture cross sections for the D-X center. The distribution is narrower for a lightly doped sample and the center of the distribution is a lower value. Our values of the capture cross section in samples doped to 1 multiplied by 1018 cm** minus **3 are lower than those previously reported. Our results in lightly doped samples are consistent with Lang's model for the D-X center.