A Two-Step-Recess Process Based on Atomic-Layer Etching for High-Performance $\hbox{In}_{0.52}\hbox{Al}_{0.48}\hbox{As}\hbox{/}\hbox{In}_{0.53} \hbox{Ga}_{0.47}\hbox{As}$ p-HEMTs

We investigated 60-nm In
_0.52
Al
_0.48
As/In
_0.53
Ga
_0.47
As pseudomorphic high-electron mobility transistors (p-HEMTs) fabricated by using a Ne-based atomic-layer-etching (ALET) technology. The ALET process produced a reproducible etch rate of 1.47 Aring/cycle for an InP etch stop layer, an excellent InP etch selectivity of 70 against an In
_0.52
Al
_0.48
As barrier layer, and an rms surface-roughness value of 1.37 Aring for the exposed In
_0.52
Al
_0.48
As barrier after removing the InP etch stop layer. The application of the ALET technology for the gate recess of 60-nm In
_0.52
Al
_0.48
As/In
_0.53
Ga
_0.47
As p-HEMTs produced improved device parameters, including transconductance (G
_M
), cutoff frequencies (f
_T
)> and electron saturation velocity (vsat) in the channel layer, which is mainly due to the high etch selectivity and low plasma-induced damage to the gate area. The 60-nm In
_0.52
Al
_0.48
As/In
_0.53
Ga
_0.47
As p-HEMTs fabricated by using the ALET technology exhibited G
_M
,
_Max
= 1-17 S/mm, f
_T
= 398 GHz, and v
_sat
= 2.5 X 10
⁷
cm/s.