Investigation of <italic>In Situ</italic> SiN as Gate Dielectric and Surface Passivation for GaN MISHEMTs

Abstract

In this paper, we present a systematic investigation of metal–organic chemical vapor deposition-grown <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> SiN as the gate dielectric and surface passivation for AlGaN/GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs). The dielectric constant and breakdown field of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> SiN were extracted from devices with varied gate dielectric thicknesses. Using frequency-dependent capacitance–voltage and parallel conductance methods, we obtained a low trap density of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 3\times 10^{12}$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-2}$ </tex-math></inline-formula> eV <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-1}$ </tex-math></inline-formula> at the SiN/AlGaN interface. The MISHEMTs with a source–drain distance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3~\mu \text{m}$ </tex-math></inline-formula> show a maximum drain current of 1560 mA/mm and a high on/off current ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{9}$ </tex-math></inline-formula> . The device 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">${V}_\textsf {th}$ </tex-math></inline-formula> ) stability was assessed by means of both negative and positive gate stress measurements, as well as temperature-dependent <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {I}_\textsf {D}$ </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">${V}_\textsf{G}$ </tex-math></inline-formula> measurements. We observed a minimal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {V}_\textsf{th}$ </tex-math></inline-formula> shift of ~0.4 V under both 3000 s gate stress of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_\textsf {GS}= 4$ </tex-math></inline-formula> V and up to 200 °C thermal stimulation. Furthermore, combining the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> SiN with plasma-enhanced chemical vapor deposition SiN, we developed a bilayer passivation scheme for effective suppression of current collapse. Employing the high-quality <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> SiN, we have demonstrated large-area GaN MISHEMTs on Si with a gate width of 20 mm, showing a low off-state leakage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2~\mu \text{A}$ </tex-math></inline-formula> /mm at 600 V and a low dynamic/static ON-resistance ratio. The device results show great advantages of employing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> SiN in D-mode GaN MISHEMTs for high-efficiency power switching applications.