In this paper, we report low frequency noise (LFN) data obtained on passivated AlGaN/GaN HEMT’s grown by MBE on a silicon substrate. In order to localize the LFN sources, we have measured all the extrinsic gate and drain current noise generators and their coherence versus bias in the linear regime. We have found that the gate noise sources result from leakage phenomena at gate-source and gate-drain regions. Drain noise sources are mostly located in the active channel below the gate and they feature an equivalent Hooge coefficient of about 10-3. Secondly, in order to build a LFN model that fits the requirements of a CAD simulator, we have measured the LFN sources for numerous bias points in the saturation region and therefore we have studied the bias dependence of the different noise sources under normal operating conditions. Results show that the gate terminal noise current impacts heavily the overall LFN of the transistor contrary to others III-V HEMTs, and that specific bias conditions are needed in order to reduce the LFN.
AlGaN/GaN HEMTs are promising devices not only for high frequency power amplification but also for non-linear applications such as VCO. Therefore an assessment of their low frequency noise (LFN) is needed since it can be up-converted around the RF carrier. We have therefore compared different devices either made on sapphire or silicon in order to know which ones feature the lowest LFN. This study involves static and low frequency noise measurements (two different LFN set-up will be used and compared). GaN HEMT devices featuring several gate dimensions have been measured for different biasing conditions both in ohmic and saturation regime. We have compared sapphire based devices with silicon based ones with respect to their LFN levels.
In a second part of this work, we report on some reliability results of HEMT on sapphire substrates: identification of defects has been achieved with the help of static measurements, and we make use of low frequency noise as well as physical simulation in order to understand the operating mode of the device. For the first time, we correlate the γ of the 1/fγ LFN spectrum with transport mechanisms of the carriers: we found that γ strongly depends on the carriers conduction path. This hypothesis has been checked for HEMT on silicon substrate.