Investigation on Traps Dynamics & Negative Bias Stress in D-Mode GaN-on-Si Power MIS HEMTs Under High-Temperature

This experimental study investigates the traps dynamics and threshold voltage (VTH) shift mechanism under negative bias temperature stress for the GaN-on-Si Power MIS HEMTs on field plate design structure. Based on the experimental analysis, two distinct activation energies (Ea) have been identified under the specific reverse bias conditions of VGS= -30 V and VDS=0 V in a wide temperature range. Reverse bias stress experiments (up to 10 ks) show a positive VTH shift of ~1.6 V at room temperature due to the inversion of the charges at the interface between the insulator and AlGaN layer, resulting in net negative charge near the gate region. Subsequently, there is a decrease in VTH shift till
$125~^{\circ }$
C because of the de-trapping of the inversion charges. This phenomenon shows a strong correlation with a thermally activated activation energy of (E
${_{\text {a}}}~\approx ~0.23$
eV). Further, the shift in
${\mathrm { V}}_{\mathrm { TH}}$
turns negative when the temperature is raised to
$175~^{\circ }$
C, indicating the accumulation of electrons in the channel layer with activation energy (E
${_{\text {a}}}~\approx ~0.78$
eV) attributed to the activation of nitrogen interstitials from the GaN buffer layer. Additionally, the recovery (up to 10 ks) behavior demonstrates the exponential-linear settlement of the traps to recover the
${\mathrm { V}}_{\mathrm { TH}}$
shift. Moreover, nitrogen interstitials take more time to suppress the threshold voltage instabilities. These findings explain the
${\mathrm { V}}_{\mathrm { TH}}$
shift mechanisms in GaN-on-Si Power MIS HEMTs under NBTI.