Electron transport properties in the Al0.15Ga0.85N/GaN heterostructure field effect transistors (HFETs) have been examined from room temperature up to 400°C. The temperature dependencies of the two-dimensional electron gas (2DEG) mobility have been systematically measured for the samples with different 2DEG densities. The 2DEG mobility has decreased with increasing the temperature, however, its decrease ratio has been no longer large above 300°C. Moreover, the 2DEG mobility has found to be less dependent on the 2DEG density at higher temperatures. These observed features indicate that the 2DEG mobility above room temperature is limited by longitudinal optical (LO) phonon scattering, as is expected by theoretical prediction. The observed 2DEG mobilities at 400°C were as high as from 100 to 120 cm2/Vs, directly providing the evidence for suitability of the HFET of this material system for high-temperature applications. The temperature dependence of the transconductance (gm) of a HFET device has also been examined up to 400°C. It has been revealed that the temperature dependence of gm has basically the same features as those of the 2DEG mobility in the corresponding temperature region.
High temperature electron transport properties in AlGaN/GaN heterostructures