Study of the effect of multiple conductions on threshold voltage in a MIS-HEMT from 450 K down to 200 K

In this work, the effect of the multiple conductions of a GaN based Metal-Insulator-Semiconductor High Electron Mobility Transistor (MIS-HEMT) when operating in a temperature range from 200K to 450K are evaluated experimentally. From 200K till 350 K the transfer curve of the 600nm gate length device shows the Zero Temperature Coefficient (ZTC) point clearly. However, for temperatures over 350 K, the threshold voltage (V-TH) shift towards higher gate voltage, which prevents the presence of ZTC bias point. This behavior is better explained through the transconductance ( gm) curve where the HEMT and MOS conductions of the devices are being affected differently by temperature, resulting in a competition of effects that changes the behavior of the device in both, gm(max) and VTH as a function of temperature.