Electrical Characterization of AlGaN/GaN-HEMTs on Semi-Insulating GaN Substrates Doped With Fe, C, or Mn and Grown by Hydride Vapor Phase Epitaxy

Abstract

This article reports a comparative study on the effect of dopants in semi-insulating GaN substrates grown by hydride vapor phase epitaxy (HVPE) on the electrical characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs). GaN-HEMTs were fabricated on GaN substrates doped with iron (Fe), carbon (C), or manganese (Mn), and their electrical characteristics from 300 to 600 K were compared. Similar on-state characteristics were observed at room temperature, regardless of the substrate dopant. However, in the off-state breakdown characteristics, the devices on the C- and Mn-doped substrates showed slightly lower gate leakage currents than those on the Fe-doped substrate. Pulsed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </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">${V}$ </tex-math></inline-formula> characteristics showed that all devices had a small current collapse of approximately 10% or less, although the devices on the C- and Mn-doped substrates had slightly larger current collapse than that on the Fe-doped substrate. Furthermore, the temperature dependence of the off-state breakdown characteristics showed that the devices on the C- and Mn-doped substrates had a breakdown voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {BD}}$ </tex-math></inline-formula> ) that exceeded 100 V, even at 600 K, while that for the device on the Fe-doped substrate was less than 20 V. Arrhenius plots of leakage current suggested that for the devices on the Fe-doped substrate, current conduction through the substrate occurred above 350 K, which resulted in a low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {BD}}$ </tex-math></inline-formula> . The devices on the C- and Mn-doped substrates had low leakage through the substrate due to the high resistivity of the substrate. These results indicate the feasibility of C- or Mn-doped GaN as HEMT substrates for use in high-voltage and high-temperature applications.

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