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 (S
_Id
/I
_d
²
) are measured and perfectly matched with both the correlated mobility fluctuations (CMF) and Hooge mobility fluctuations (HMF) noise models. From the curves of (S
_Id
/I
_d
²
) dependent on the gate overdrive voltage (V
_g
- V
_th
)
^-1
, it is also confirmed that the mobility fluctuations prevail in the fabricated GaN device. The calculated Hooge constants (α
_H
) according to the (V
_g
- V
_th
) are obtained to be 10
^-2
~ 10
^-3
. The reason for the dominance of the mobility fluctuations and the relatively low α
_H
is attributed that the TMAH wet etching effectively removes the plasma etching damage and fully recovers the crystal quality of GaN channel.