Characterization of Dynamic $R_{\text{ON}}$ in GaN HEMTs

GaN HEMTs, featuring low gate charge, low output capacitance and near-zero reverse recovery charge, enable fast switching speed and low switching losses and are desirable for power electronic systems with high power density and energy efficiency. Nevertheless, GaN-on-Si HEMTs are confronted with the primary challenge of dynamic on-resistance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(R_{\text{ON}})$</tex> degradation, which arise from buffer trapping, surface trapping and gate instability. In this article, we discuss dynamic <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$R_{\text{ON}}$</tex> degradation of GaN HEMTs, review our recent progresses in revealing key mechanisms of the operating state of p-GaN drain (PD) structure under various switching conditions and its impact on dynamic <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$R_{\text{ON}}$</tex>, including temperature, off-state voltage <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(V_{\text{OFF}})$</tex> stress, hard-/soft-switching, current transients during hard-switching and on-state current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(R_{\text{ON}})$</tex>. It has been found that hole injection from the PD structure plays an important role in compensating the negative trapped charges and alleviating dynamic <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$R_{\text{ON}}$</tex> degradation, particularly at elevated temperature, higher <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{\text{OFF}}$</tex> and larger <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$I_{\text{ON}}$</tex>. These works provide valuable insights for the in-depth understanding of PD structure and development of GaN HEMT with superior dynamic performance in high-temperature and high-power applications.