High RF Performance E-Mode GaN-on-Si HEMTs With Pₒᵤₜ of 5.32 W/mm Using High-Quality Ultrathin Buffer

Abstract

In this letter, we report a high-performance enhancement-mode GaN HEMT fabricated on high-quality ultrathin buffer, which achieved by a two-step-graded (TSG) transition structure on high-resistivity (HR) silicon substrate. Owing to rapid dislocation annihilation of TSG transition structure, the ultrathin buffer exhibits a low total dislocation density (TDD) of ${1}.{7}\times {10} ^{{9}}$ cm $^{-{2}}$ , which could make a contribution to the improvement of current and RF power performance. As a result, an E-mode GaN HEMT fabricated on this structure presents a maximum drain current of 620 mA/mm, a threshold voltage ( ${V}_{\text {th}}\text {)}$ of 0.7 V, and a transconductance of 360 mS/mm. Furthermore, load-pull measurements yield a maximum output power density ( ${P}_{\text {out}}\text {)}$ of 5.32 W/mm at 3.6 GHz and ${V}_{\text {DS}}=35$ V in pulse mode, which represents the top level for E-mode GaN-on-Si devices reported to date. The high-quality GaN epitaxy and splendid E-mode HEMT shown in this work reveal great potential for GaN-on-Si RF applications.