Characterization of deep levels in modulation-doped AlGaAs/GaAs FET's

Deep levels in modulation-doped field-effect transistors (MODFET's) fabricated from MBE-grown AlGaAs/GaAs heterostructures, have been characterized by a modified deep-level transient spectroscopy (DLTS) technique. Assuming donor-like traps in the AlGaAs layer, it is shown that the threshold voltage V
t
varies exponentially with time under pulsed-biased conditions. This result is verified experimentally by observing the transient in the drain current I
D
in long-gate FET's biased in saturation. The resulting Δ √{I_{D}} DLTS spectrum reveals an electron trap with an activation energy of 0.472 eV in Si-doped Al
0.3
Ga
0.7
As.