Superlattice conduction in superlattice modulation-doped field-effect transistors

Abstract

We fabricated superlattice modulation-doped field-effect transistors where the doping is concentrated in GaAs narrow quantum wells separated by undoped AlGaAs barriers. As the doped AlGaAs regions are eliminated from such a structure, the concentration of traps generally associated with doping of AlGaAs is low. We observed the threshold voltage shift of only 140 mV with temperature change from 77 to 300 K (which should be compared to the shift of 200–300 mV in conventional modulation-doped field-effect transistors). Peak transconductances of 310 mS/mm at 300 K and 321 mS/mm at 77 K have been obtained. An interesting feature of this device is the complicated dependence of the transconductance on the gate voltage which has two peaks at 77 K and one sharp peak at 300 K. These peaks are caused by the parallel conduction paths in the superlattice at high gate voltages and by the gate leakage current. This parallel conduction in GaAs-doped quantum wells may be used in order to achieve larger voltage swings in superlattice modulation-doped field-effect transistors.