Demonstration of High-Current E-Mode MOSFETs Using Heteroepitaxial ε-Ga₂O₃ on 4H-SiC Substrates

High-current enhancement mode (E-mode) metal-oxide-semiconductor field effect transistors (MOSFETs) have been demonstrated using heteroepitaxial <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon $ </tex-math></inline-formula>-Ga2O3 on 4H-SiC substrates. The devices featured an unintentionally-doped (UID) channel and ultra-highly conductive access regions, which were realized by a selective-area fluorine-plasma surface doping process. In the access regions, a high sheet carrier concentration (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${n}_{\text {s}}\text {)}$ </tex-math></inline-formula> exceeding <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${3}\times {10} ^{{14}}$ </tex-math></inline-formula> cm−2 combined with a mobility of 47.1 cm2/V<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> s was achieved, significantly reducing the parasitic resistance. The fabricated E-mode MOSFET with a channel length (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {CH}}\text {)}$ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2~\mu $ </tex-math></inline-formula>m exhibited a high maximum drain current density (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {DS, max}}\text {)}$ </tex-math></inline-formula> of 209 mA/mm, a positive threshold voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}\text {)}$ </tex-math></inline-formula> of 2.7 V, a large peak transconductance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${G}_{\text {m, max}}\text {)}$ </tex-math></inline-formula> of 42 mS/mm, and a high on/off current ratio (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {on}}$ </tex-math></inline-formula>/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {off}}\text {)}$ </tex-math></inline-formula> exceeding <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{7}}$ </tex-math></inline-formula>. These competitive performance metrics are mainly attributed to the low parasitic resistance in the access regions and the high thermal conductivity of the 4H-SiC substrate, highlighting the great potential of heteroepitaxial <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon $ </tex-math></inline-formula>-Ga2O3-on-4H-SiC MOSFETs for high-power and high-frequency applications.