Gate defects in AlGaN/GaN HEMTs revealed by low frequency noise measurements

From the last decade, Nitride-based High Electron Mobility Transistors (HEMTs) have demonstrated excellent electrical and noise performances to address transceivers modules. Within this paper, a discussion on the low frequency noise on the gate access (i.e. gate current spectral density S_IG) in the frequency range of 1Hz-100kHz is presented. S_IG spectra reveal different signatures according to the configuration of biasing of the transistor, and to the dimensions of the transistor: the noise of the Schottky diode is studied alone (under open drain configuration), and compared with S_IG of the transistor biased in the saturated region (at V_Ds=8V). Two designs of devices are tested: research-level devices featuring single gate finger are compared with commercial devices featuring four gate fingers, where each finger is four times larger (i.e. 16 times larger gate width than research level devices). The two sets of devices followed the same fabrication process. It is found that whatever the sizing and the gate pad configuration of the devices, the LFN spectra observed on each set of transistors feature identical signatures. The leakage carriers are following the same path between the gate and source accesses. LFN can be used as an accurate tool to discriminate between conduction mechanisms of devices, and to help to understand what are the underlying mechanisms leading to the conduction of the Schottky diode (and thus to its degradation). Moreover, it is shown that the S_IG measurements under transistor biasing conditions can be correlated to the gate current spectral density in diode mode: the leakage current zone can also be tracked under this biasing operating mode.