Trapping effects at the drain edge in 600 V GaN-on-Si HEMTs

In this paper, we investigate the influence of the drain electrode on the dynamic switching behavior of AlGaN/GaN high-electron-mobility transistors on Si substrate. By adding a field plate to the drain electrode, a dramatic increase in the dynamic ON-resistance dynR (mathon) was identified. The dispersion effect is correlated with the high electric field below the drain field plate (DFP), the onset of which is caused by the full electron depletion from both the channel and the GaN cap layer. We show that the electron distribution is modified by the passivation method, backside bias, or surface charges and, hence, shifts the onset voltage of the trapping effect. Trapped electrons underneath the DFP are thought to be responsible for the measured rise of the dynR (mathon). With the introduction of an extended ohmic drain contact, the influence of a metallization overhang at the drain edge can be suppressed. The detrapping energies associated with the surface defects were determined to 0.2, 0.3, and 0.7 eV, respectively. Simulations and measurements indicate that charges in-side the passivation below the DFP worsen the switching behavior.