Temperature dependence of Ohmic contact characteristics in AlGaN/GaN high electron mobility transistors from −50 to 200 °C

Abstract

The temperature dependent characteristics of Ti/Al/Ni/Au Ohmic contact for AlGaN/GaN high electron mobility transistors (HEMTs) on high-resistivity Si and sapphire substrates were investigated over the temperature range from −50 to 200 °C. The sheet resistances (Rsh) of AlGaN/GaN HEMTs on Si and sapphire substrates were found to increase with the temperature according to the power-law equation with power indices of −2.7 and −2.3, respectively. The specific contact resistivity (ρC) decreased with the temperature, and it was observed to be determined by the electron thermionic field emission (TFE) from the lowered conduction band edge in the modified AlGaN region with high-density N-vacancies to the quantum well at the AlGaN/GaN heterojunction with two dimensional electron gas (2DEG). Three important parameters in the TFE are extracted, that is, the barrier height (ϕB) of around 0.5 eV, the energy difference between the effective conductive-band edge and the Fermi level in 2DEG (En) of around 0.1 eV, and the 2DEG electron density (ND) with the order of magnitude of 1019 cm−3.