Gate voltage dependence of low frequency noise of AlGaN/GaN HEMTs
Low frequency noise measurements have been widely used to investigate the nature of defects in semiconductor devices. Characterization of low frequency noise performance at different gate bias along with the temperature is very useful to study and identify the defects in the devices. In this work, the frequency, gate bias and temperature dependence of low frequency noise of three differently processed AlGaN/GaN high electron mobility transistors (HEMTs) have been evaluated. Both the frequency-dependence and gate-voltage dependence of the low frequency noise of AlGaN/GaN HEMTs are difficult to understand within the context of the popular Hooge mobility fluctuation model. Instead, the noise is consistent with a carrier-number fluctuation model that includes a non-constant defect-energy distribution Dt(Ef ). A strongly varying Dt(Ef ) in these devices is confirmed by measurements of the temperature dependence of the noise. Estimates of the effective border-trap density before and after 1.8 MeV proton irradiation are provided for both commercial and research-grade devices using a number-fluctuation model. The input-referred noise magnitude for AlGaN/GaN HEMTs decreases at biases that are significantly more positive than the threshold voltage because the gated region of the HEMT comprises a relatively small portion of the channel, and the noise is attenuated by the voltage divider formed by the gated and ungated regions of the channel.