Investigation of 1/f and Lorentzian Noise in TMAH-treated Normally-Off GaN MISFETs

A tetramethyl ammonium hydroxide (TMAH)-treated normally-off Gallum nitride (GaN) metal-insulator-semiconductor field-effect transistor (MISFET) was fabricated and characterized using low-frequency noise (LFN) measurements in order to find the conduction mechanism and analyze the trapping behavior into the gate insulator as well as the GaN buffer layer. At the on-state, the noise spectra in the fabricated GaN device were 1/fγ properties with γ ≈ 1, which is explained by correlated mobility fluctuations (CMF). On the other hand, the device exhibited Lorentzian or generation-recombination (g-r) noises at the off-state due to deep-level trapping/de-trapping into the GaN buffer layer. The trap time constants (τi) calculated from the g-r noises became longer when the drain voltage increased up to 5 V, which was attributed to deep-level traps rather than shallow traps. The severe drain lag was also investigated from pulsed I-V measurement, which is supported by the noise behavior observed at the off-state.