Non-uniform degradation behavior across device width in RF power GaAs PHEMTs

We have studied the electrical degradation of RF power PHEMTs by means of light-emission measurements performed during bias-stress experiments. We show that electrical degradation can proceed in a highly non-uniform manner across the width of the device. We identify the origin of this as a small systematic non-uniformity in the recess geometry that impacts the electric field and the impact ionization rate on the drain of the device. Our research suggests that a close examination of the width distribution of electric field in RF power PHEMTs (and FETs in general) is essential to enhance their long-term reliability