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

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
${I}$
–
${V}$
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 (
${V}_{\text {BD}}$
) 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
${V}_{\text {BD}}$
. 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.