Characterization of flicker noise in GaN-based MODFET's at low drain bias

We report systematic characterizations of flicker noise in GaN based MODFET's. The devices were fabricated by MBE on (0001) basal plane sapphire substrates with an 800 /spl Aring/ AlN buffer layer grown at 800/spl deg/C. Flicker noise was measured across the channel of the devices from room temperature to about 130 K. The voltage noise power spectra, S/sub V/(f), were found to be proportional to 1/f/sup /spl gamma//. The frequency exponent, /spl gamma/, of S/sub V/(f) exhibits systematic dependencies on the device temperature as well as the gate bias, V/sub G/. The variation of the noise power spectra as a function of the drain voltage, V/sub D/, and the gate bias, V/sub G/, were studied in detail and were found to vary as V/sub D//sup 2//(V/sub G/-V/sub T/)/sup /spl beta// where /spl beta/ changes with temperature from about 2.1 at room temperature to about 0.9 at 130 K. Analyses of the data show that the noise originated from the thermal activation of carriers to the localized states at the AlGaN/GaN heterointerface in the channel area. The data suggested that the trapping and detrapping of carriers did not lead to fluctuations in the carrier concentration as postulated in the McWhorter's model. However, more work is needed to determine if surface mobility fluctuations played a key role in the 1/f noise.