University of Illinois Urbana-Champaign

Demystifying metal-assisted chemical etching of III-N materials and multi-heterojunctions: fundamentals to optoelectronic applications

Chan, Clarence Yat-Yin

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https://hdl.handle.net/2142/122156

Description

Title
Demystifying metal-assisted chemical etching of III-N materials and multi-heterojunctions: fundamentals to optoelectronic applications
Author(s)
Chan, Clarence Yat-Yin
Issue Date
2023-12-01
Director of Research (if dissertation) or Advisor (if thesis)
Li, Xiuling
Doctoral Committee Chair(s)
Li, Xiuling
Committee Member(s)
  • Lee, Minjoo Lawrence
  • Lyding, Joseph W
  • Coleman, James J
Department of Study
Electrical & Computer Eng
Discipline
Electrical & Computer Engr
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
  • Semiconductor Processing
  • Wet Etching
  • Photoelectrochemical Etching
  • Metal-assisted Chemical Etching
  • GaN
  • III-N Materials
  • Optoelectronics
  • microLED
Abstract
III-Nitride electronics have undergone a rapid pace in development since their adoption in light-emitting diode (LED) technologies towards the turn of the 21st century. Over 20 years later, they are found in numerous consumer applications atop of their original application in solid-state lighting. These include closely related applications for light-emitters in display technologies, as well as usage in high power, temperature, and frequency electronics most notably in power and RF transistors. Inevitably with performance enhancement requirements, nitride electronics will undergo similar scaling requirements as silicon has over the course of the past six decades. Like silicon, nitride materials are currently micro-machined by plasma dry-etch technologies commonly generalized as reactive ion etching (RIE). Much like silicon, nitride materials also face challenges to device scaling due to material damage from the RIE process. This is most evident in the reduction of device performance in µLEDs, often touted as the next major display technology following the mass market adoption of organic LEDs (OLEDs), particularly for emerging applications in augmented, virtual, and mixed reality (AR / VR / MR) display space. While cost reduction is expected with advancements in both growth and device transfer processes, the performance gains from device scaling have yet to live up to expectations. A key barrier to this is the increase in surface-to-volume ratio as devices shrink allowing for enhanced Shockley-Read-Hall (SRH) recombination from defect states present in the mesa sidewall surface as well as sub-surface rendering an increasing portion of the device inoperable. The largest source of defect state generation is the aforementioned plasma damage induced by reliance on RIE for micro-machining. To combat this issue, metal-assisted chemical etching (MacEtch) was developed as a plasma-free, anisotropic wet etching method originally in silicon and expanded to phosphides, arsenides, as well as wide band-gap semiconductors such as nitrides, silicon carbide and gallium oxide. While MacEtch and similar photoelectrochemical (PEC) etching methods have long been studied in GaN, ironically from roughly the same time period as its adoption in LEDs, there has never been a systematic breakdown of its core mechanics with understanding of the process seemingly as scattered as RIE early in its development during the late 1960s and early 1970s. Applications of MacEtch and PEC etching in III-nitrides have thus far been limited to passive structures or lift-off processes restricted to singular nitride materials rather than multi-heterojunctions and certainly not for device relevant structures. In this dissertation, the core mechanics of MacEtch in III-N materials is systematically broken down into its respective governing parameters. Furthermore, system components for MacEtch are correlated to fundamental electronic effects independent of material allowing application to other wide bandgap semiconductors and PEC processes beyond etching. In addition, the extension of MacEtch beyond bulk materials to multi-heterojunctions will be discussed for structures encompassing the AlInGaN system with varying alloy compositions. Discussion of process differences between multi-heterojunctions and bulk materials and their effects on etching will be included, along with investigation of necessary changes to etch chemistry away from what is established. Finally, the first ever application of MacEtch in the fabrication of a µLED (or any III-N based device) will be presented ranging from process integration to comparisons to RIE. Device testing and results will also be presented and compared to results obtained by current process methods.
Graduation Semester
2023-12
Type of Resource
Thesis
Copyright and License Information
Copyright 2023 Clarence Yat-yin Chan

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