Drain resistance degradation under high fields in AlInAs/GaInAs MODFETs

Lattice-matched AlInAs/GaInAs modulation-doped FETs (MODFETs) demonstrate excellent high-frequency, small-signal performance. However, high-power, large-signal applications of these devices may be limited. Impact ionization and tunneling reduce the breakdown voltage, which limits the upper end of the output voltage swing, thus reducing the output power. Our results indicate that the lower end of the voltage swing (knee voltage) is also degraded by increased drain resistance when impact ionization occurs. In this work, we correlate R_d degradation in the AlInAs/GaInAs material system to the presence of impact ionization. The magnitude of R_d degradation depends on the applied drain bias and drain current. These factors affect the degree of impact ionization, and thus the extent of the degradation. Since R_d increases and R_s does not, only the high field side of the FET is affected. This increase in R_d is attributed to a wider carrier depletion region between the gate and drain after stress, which results in reduced device performance