Evaluating the Effect of the Varying Field Plate's Length on the Performance of a GaN HEMT with a Graded AlGaN Back Barrier

This work investigates the DC and AC characteristics of a GaN HEMT without a field plate (FP) and a proposed GaN HEMT with a gate field plate (GFP) in TCAD simulation tool. GFP length increases by 50, 100, and 100 nm toward the drain. The ON state current of GaN HEMTs without FP is 1.28 A/mm, but with GFP lengths of 50, 100, and 150 nm, it decreases to 4, 8, and 11 %, respectively. The suggested GFP device's leakage current is 4.85, 3.85, and 3.55 A/mm for GFP lengths of 50, 100, and 150 nm, respectively, compared to the device without FP (5.91 A/mm). The transconductance of the devices decreases with increasing GFP due to decreased <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\mathrm{d}\mathrm{s}}$</tex>, with values of 200, 188, 176, and 165 mS/mm. An AC analysis is conducted to assess how the field plate (FP) affects the gate capacitance ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{C}_{\mathrm{g}\mathrm{g}}$</tex> ) in GaN HEMTs. The inclusion of the field plate increases the gate-to-gate capacitance ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{C}_{\mathrm{g}\mathrm{g}}$</tex> ). GaN HEMTs without FP have a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{C}_{\mathrm{g}\mathrm{g}}$</tex> of 12 pF/mm. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{C}_{\mathrm{g}\mathrm{g}}$</tex> values for GaN HEMTs with varying GFP lengths are: 1.35 pF/mm for 50 nm, 1.46 for 100 nm, and 1.55 for 150 nm.