Admittance frequency dispersion in lateral AlGaN/GaN Schottky barrier diodes: Other origins of two Gp/ω peaks

The frequency dispersion in admittance measurements in AlGaN/GaN high-electron-mobility transistors, which is typically interpreted to result from an interface trap density D-it, is also known to be caused by effects other than D-it. To study the origin of two peaks of conductance component "Gp/omega " as a function of frequency in lateral gated diodes using AlGaN/GaN structures on Si wafers grown by metal-organic chemical vapor deposition, we measured capacitance C and conductance Gp/omega-voltage V as a function of angular frequency omega (C-omega-V and Gp/omega-omega-V, respectively) of long-gate field-effect transistors with a varied gate length. We also simulated the C-omega-V and Gp/omega-omega-V curves using an equivalent circuit that consisted of actually measured component parameters without D-it. We confirmed that the Gp/omega-omega curves show two peaks caused by the two-dimensional electron gas channel resistance and the gate current leakage and quantitatively determined the two omega(peak) positions and intensities. We also discussed the effect of acceptor concentration in the GaN channel-layer on lowering of omega(peak) at weak inversion.