Measurement of the electron velocity-field characteristic in modulation-doped structures using the geometrical magnetoresistance method

We describe a method for measuring the electron mobility, velocity, and sheet carrier concentration in modulation-doped structures as functions of electric field through the use of the geometrical magnetoresistance effect. Because the geometry of the structures is identical to that of ungated FET's, these measurements are well suited for studying the electron velocity in MODFET's. We see that the mobility quickly decreases from its low field value with increasing electric field and observe significant electron injection from the contacts. The electron velocity increases to about 1.4 × 10
⁷
cm/s at 3000 V/cm at 77 K before domain formation prevents accurate measurements at higher fields.