GaN High-Electron-Mobility-Transistor on Free- Standing GaN Substrate With Low Contact Resistance and State-of-the-Art fT × LG Value

In this article, we report on demonstrating high-performance AlGaN/GaN high-electron-mobility-transistor (HEMT) on free-standing GaN (FS-GaN) substrate with low contact resistance (
${R}_{C}$
) and high breakdown voltage (BV). Non-regrowth
${R}_{C}$
as low as
$0.23 \Omega \cdot $
mm was achieved by using the self-aligned Ohmic etching process and nonfield plated BV as high as 193 V was also acquired due to the low dislocation density of the epi-layer on FS-GaN substrate. It is found that the reduction of the
${R}_{C}$
is induced by the smaller electron tunneling width across the AlGaN barrier layer, rather than the formation of dislocation related metal spikes. The fabricated GaN HEMT was a peak extrinsic transconductance (
${g}_{m}$
) of 203 mS/mm and a drain current (
${I}_{D}$
) ON/OFF ratio of 10
⁶
–10
⁷
. Benefited from the low
${R}_{C}$
, a cut-off frequency/maximum oscillation frequency (
${f}_{T}/{f}_{max}$
) of 26/73 GHz was extracted at a gate length (
${L}_{g}$
) of 600 nm, yielding a
${f}_{T}\cdot {L}_{g}$
value of 15.6 GHz
$\cdot \mu \text{m}$
and a Johnson’s figure-of-merit (J-FOM) of 5.0 THz
$\cdot \text{V}$
, which are the highest values among all AlGaN/GaN HEMTs on FS-GaN substrate. This work implies that GaN HEMTs on FS-GaN substrate with low
${R}_{C}$
turn out to be a promising candidate for high-performance radio frequency (RF) power device applications.