A Normally-Off GaN MIS-HEMT Fabricated Using Atomic Layer Etching to Improve Device Performance Uniformity for High Power Applications

Normally-off ferroelectric charge trap gate stack GaN high electron mobility transistor (FEG-HEMT) was fabricated with atomic layer etching (ALE) to precisely control the device parameters including
$\text {V}_{\text {th}}$
of the device. The ALE process consists of cyclic Cl2 adsorption modification steps and the Ar ion removal steps. The ALE process achieved etch-per-cycle (EPC) of 0.347 nm/cycle and superior etching morphology with RMS
$=0.281$
nm. The fabricated GaN HEMT using the ALE process exhibited a high threshold voltage (
$\text {V}_{\text {th}}$
) of 5.06 V, high maximum drain current (
$\text {I}_{\text {D,MAX}}$
) of 772 mA/mm with low on-resistance (
$\text {R}_{\text {on}}$
) of
$8.57~\Omega \cdot \text {mm}$
and high breakdown voltage (BV) of 888 V, the device also showed good
$\text {V}_{\text {th}}$
uniformity. Finally, the contact resistance (
$\text {R}_{\text {c}}$
) was reduced from
$0.46~\Omega \cdot \text {mm}$
to
$0.15~\Omega \cdot \text {mm}$
by the ALE process, and the dynamic on-resistance (dyn-
$\text {R}_{\text {on}}$
) was improved at the same time.