Mobility Fluctuations in a Normally-Off GaN MOSFET Using Tetramethylammonium Hydroxide Wet Etching

Low-frequency noise (LFN) performances are investigated in a normally-off GaN metal-oxide-semiconductor field-effect transistor (MOSFET) fabricated by utilizing the tetramethylammonium hydroxide (TMAH) wet etching. The normalized power spectral densities (SId/Id2) are measured and perfectly matched with both the correlated mobility fluctuations (CMF) and Hooge mobility fluctuations (HMF) noise models. From the curves of (SId/Id2) dependent on the gate overdrive voltage (Vg- Vth)-1, it is also confirmed that the mobility fluctuations prevail in the fabricated GaN device. The calculated Hooge constants (αH) according to the (Vg- Vth) are obtained to be 10-2~ 10-3. The reason for the dominance of the mobility fluctuations and the relatively low αHis attributed that the TMAH wet etching effectively removes the plasma etching damage and fully recovers the crystal quality of GaN channel.