Impact of Fin Width on Low-Frequency Noise in AlGaN/GaN FinFETs: Evidence for Bulk Conduction

AlGaN/GaN Fin-shaped field-effect transistors (FinFETs) with nano-sized Fin width (
$\text{W}_{\mathrm {Fin}}$
) from 20 nm to 230 nm are characterized using low-frequency noise (LFN) measurement. All devices exhibit 1/
$f$
noise shape with Hooge mobility fluctuations (HMF) at subthreshold region and carrier number fluctuations (CNF) at accumulation region. However, the lowest normalized drain current noise spectral densities (
$S_{Id}/I_{d}^{2}$
) are obtained in the narrow Fin device (
$\text{W}_{\mathrm {Fin}}$
= 20 nm). This is due to significant contribution of bulk channel without the 2-dimensional electron gas density (2DEG) channel and two sidewall metal-oxide-semiconductor (MOS) channels. It is also noticed that the lowest trap density (
$N_{t}$
) and a large separation in CNF noise model clearly indicate to the volume accumulation effect caused by bulk conduction in narrow device. The Hooge constants (
$\alpha _{\mathrm {H}}$
) extracted by HMF noise model for the narrow device are one-order higher than those of the wide Fin device, which tells that the narrow device suffers from the strong phonon scattering in the bulk channel. From the product of (
$S_{Id} \times $
frequency (
$f$
)) versus
$\text{I}_{\mathrm {d}}$
curves, the volume accumulation phenomenon is also clearly observed in narrow Fin device.