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 × 10⁷cm/s at 3000 V/cm at 77 K before domain formation prevents accurate measurements at higher fields.