Improved Breakdown Voltage and RF Power Characteristics of GaN HEMTs by Layered C/Fe-Doped GaN Buffer

In this article, an innovative layered GaN buffer is proposed. The upper layer is low-concentration C-doped, and the lower layer is the Fe-doped GaN buffer layer used in AlGaN/GaN high electronic mobility transistors (HEMTs). While suppressing the Fe doping tail, the breakdown voltage of the GaN HEMT is increased from 128 to 174 V. Because of the suppression of the Fe-doped tail, the mobility and transconductance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {g}_{m}\text {)}$ </tex-math></inline-formula> were also significantly improved. The C-doped concentration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${5}\times {10}^{{16}}$ </tex-math></inline-formula>/cm3 does not significantly worsen the current collapse (CC) of the GaN HEMTs. The CC of C/Fe-doped GaN HEMTs is 3% at the (−3.5, 20) V. The increase in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {g}_{m}$ </tex-math></inline-formula> results in a higher current gain cut-off frequency (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{T}\text {)}$ </tex-math></inline-formula> and the maximum oscillation frequency (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\max }\text {)}$ </tex-math></inline-formula>. The C/Fe-doped buffer GaN HEMTs exhibit high performance in the RF load-pull of 12 GHz. The 24.1 W/mm of output power density and 57% of power-added efficiency (PAE) are realized at 80 V of drain voltage. This can provide a new idea for the buffer layer of high RF power GaN HEMTs.