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A set of explicit analytical solutions to the charge concentration, current, and capacitance characteristics of AlGaN/GaN MODFETs in different working regions is developed. First, a unified charge control expression applicable to both subthreshold regions and strong inversion regions is determined, while the parasitic channel effect in AlGaN layer is also taken into account. The onset voltage for this parasitic channel is estimated for the first time. Based on the improved charge control model, the current (I ds), the transconductance (gm), and the output conductance (gd) are given explicitly and are applicable in a wide bias range. Moreover, the gate-to-source capacitance (C gs ) and gate-to-drain capacitance (C gd) have been obtained analytically under various applied biases, and, consequently, the cutoff frequency can be predicted. The present model shows good agreement with the experimental data and is useful for microwave circuit design and analysis.
Date of Publication: Dec. 2009