High temperature behaviour of GaN HEMT devices on Si(111) and sapphire substrates

A study of the high temperature DC performance of nitride high electron mobility transistors (HEMTs) on Si(111) and sapphire substrates with different gate lengths is reported. All single gate transistors decrease their drain current (I D ) and transconductance (g m ) from room temperature (RT) up to 350 °C, mainly due to the electron mobility reduction by optical phonon scattering. At RT, HEMTs on Si(111) present higher I D and g m than transistors on sapphire, probably related to their lower self‐heating. As devices are heated, these differences tend to disappear, indicating that the substrate thermal conductivity becomes less important. Compact devices have low relative reduction in I D and g m values with temperature, since shorter gate lengths lead to higher fields under the gate and lower temperature dependence of the drift velocity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)