Scalable nanofabrication techniques for III-V compound semiconductors and dielectrics

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Realization of the newest photonic and electronic nanostructures and devices requires overcoming the limits of present nanofabrication techniques. This thesis presents scalable techniques to fabricate III-V compound semiconductor and dielectric nanostructures.  The central techniques developed in this work are: (1) a method for fabricating large-area position-controlled GaAs nanowire arrays using azopolymers with laser interference lithography (LIL) followed by dry etching and metalorganic vapour phase epitaxy (MOVPE), (2) a new type of low refractive index nanoporous conformal antireflection (AR) coating for glass called grass-like alumina with broadband omnidirectional transmittanceand is made from de-ionized water treated atomic layer deposited alumina, and (3) the atomic layer etching process for the GaN (0001) crystal plane.  The significance of the large-area position-controlled GaAs nanowire arrays is that such high-surface-area, low-volume GaAs nanowire arrays can be used for example in next generation inexpensive and efficient solar cells.  The grass-like alumina presents a paradigm shift on optical coatings as it is suitable for production of hundreds of optical components coated in parallel conformally even on surfaces where no other technique is available due to extreme topography. The grass-like alumina on glass has a graded refractive index profile and acts as an AR coating enabling broadband and omnidirectional transmittance in the visible spectrum of light. What is remarkable is that a completely new type of behaviour was found from such a well known and widely used material as ALD alumina.  GaN (0001) atomic layer etching (ALE) process was developed, which can remove one molecular layer of GaN at a time and is suitable for fabrication of atomic fidelity nanostructures and normally-off high electron mobility transistors, using conventional photoresists as etch masks. This expertize was further used in analyzing ALE of silicon for nanoscale pattern transfer and high-resolution nanoimprint stamp preparation.  In addition to developing the GaN ALE process for the (0001) crystal plane other III-N technologies were developed. GaN growth on silicon on insulator wafers was demonstrated and the films characterized, and N-polar AlN growth on 4H-SiC was characterized.
Translated title of the contributionSkaalattavia nanovalmistustekniikoita III-V-yhdistepuolijohteille ja dielektreille
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Sopanen, Markku, Supervising Professor
Publisher
Print ISBNs978-952-60-8351-3
Electronic ISBNs978-952-60-8352-0
Publication statusPublished - 2018
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • GaAs
  • nanowire
  • ALD
  • gradient refractive index
  • GaN
  • atomic layer etching

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