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

Abstract

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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {V}_{\text {th}}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=0.281$ </tex-math></inline-formula> nm. The fabricated GaN HEMT using the ALE process exhibited a high threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {V}_{\text {th}}$ </tex-math></inline-formula> ) of 5.06 V, high maximum drain current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {I}_{\text {D,MAX}}$ </tex-math></inline-formula> ) of 772 mA/mm with low on-resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {R}_{\text {on}}$ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8.57~\Omega \cdot \text {mm}$ </tex-math></inline-formula> and high breakdown voltage (BV) of 888 V, the device also showed good <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {V}_{\text {th}}$ </tex-math></inline-formula> uniformity. Finally, the contact resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {R}_{\text {c}}$ </tex-math></inline-formula> ) was reduced from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.46~\Omega \cdot \text {mm}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.15~\Omega \cdot \text {mm}$ </tex-math></inline-formula> by the ALE process, and the dynamic on-resistance (dyn- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {R}_{\text {on}}$ </tex-math></inline-formula> ) was improved at the same time.