Crystals (May 2024)

Demonstration of HCl-Based Selective Wet Etching for N-Polar GaN with 42:1 Selectivity to Al<sub>0.24</sub>Ga<sub>0.76</sub>N

  • Emmanuel Kayede,
  • Emre Akso,
  • Brian Romanczyk,
  • Nirupam Hatui,
  • Islam Sayed,
  • Kamruzzaman Khan,
  • Henry Collins,
  • Stacia Keller,
  • Umesh K. Mishra

DOI
https://doi.org/10.3390/cryst14060485
Journal volume & issue
Vol. 14, no. 6
p. 485

Abstract

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A wet-etching technique based on a mixture of hydrochloric (HCl) and nitric (HNO3) acids is introduced, demonstrating exceptional 42:1 selectivity for etching N-polar GaN over Al0.24Ga0.76N. In the absence of an AlGaN etch stop layer, the etchant primarily targets N-polar unintentionally doped (UID) GaN, indicating its potential as a suitable replacement for selective dry etches in the fabrication of GaN high-electron-mobility transistors (HEMTs). The efficacy and selectivity of this etchant were confirmed through its application to a gate recess module of a deep-recess HEMT, where, despite a 228% over-etch, the 2.6 nm AlGaN etch stop layer remained intact. We also evaluated the proposed method for the selective etching of the GaN cap in the n+ regrowth process, achieving a contact resistance matching that of a BCl3/SF6 ICP process. These findings underscore the applicability and versatility of the etchant in both the electronic and photonic domains and are particularly applicable to the development of N-polar deep-recess HEMTs.

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