Effect of buffer thickness on DC and microwave performance of AlGaN/GaN heterojunction field‐effect transistors

Abstract

AbstractThe authors compared DC and microwave performance of AlGaN/GaN heterojunction field‐effect transistors (HFETs) fabricated on epitaxial structures with different thickness of GaN buffer layer. The structures were grown by low‐pressure metal‐organic vapour phase epitaxy on semi‐insulating SiC substrates. An increase of the average off‐state breakdown voltage from 39 to 142 V with reduction of buffer thickness from 1.5 to 0.5 µm was measured. The increase of breakdown voltage was explained by reduction of buffer leakage current due to higher concentration of dislocations threading to the surface of thin buffer. Our results revealed no degradation of AlGaN/GaN interface and device performance including dispersion for the case of reduced buffer thickness. A comparison of the electron sheet resistance, maximum drain‐to‐source current, transconductance, threshold voltage, gate and drain leakage currents is provided. RF maximum power performance was improved by ∼1 W/mm with higher power added efficiency for transistors fabricated on epitaxial structure with 0.5‐µm‐thick GaN buffer. Current slump was measured by pulsed I–V characteristics. A nearly unchanged dispersion demonstrated the possibility of GaN buffer thickness reduction approach for suppression of punch‐through effect without compromise in current collapse commonly observed in GaN‐based HFETs.