Thermal and plasma-enhanced atomic layer deposition: the study of and employment in various nanotechnology applications

Research output: ThesisDoctoral ThesisCollection of Articles

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Abstract

This thesis focuses on atomic layer deposition (ALD) and presents results divided between two parts. The first part examines plasma-enhanced atomic layer deposition (PEALD) of AlN and the effects processing conditions have on material properties and growth. The second part focuses on the employment of various ALD thin films for diverse nanotechnology applications. For PEALD AlN films deposited using a capacitively coupled plasma source it was demonstrated that the choice of plasma gas, processing temperature, and plasma bias voltage have a marked effect on the growth and physical properties. PEALD AlN was further investigated as a dry etch mask for SF6-based silicon plasma etching. Experiments using inductively coupled plasma-reactive ion etch and reactive ion etch systems show the material to be an excellent hard mask, akin to ALD Al2O3. A surface stack consisting of PEALD AlN and ALD HfO2 was deposited on GaAs to form high-k metal insulator semiconductor capacitors. Surface passivation of GaAs by PEALD AlN was established by showing Fermi level unpinning at the interface using capacitance-voltage and current-voltage measurements. ALD Al-doped ZnO (AZO) was investigated as a platform for GaAs nanowire (NW) growth on a variety of materials not normally conducive to NW growth. The GaAs NWs were uniform irrespective of the underlying substrate. Photoluminescence measurements indicate the NWs incorporated Zn from AZO and illuminated even at room temperature. ALD TiO2 and Al2O3 were studied as intermediary layers between ZnO nanorods (ZnOr) and a porphyrin based organic layer. Fluorescence measurements indicate that a 5 nm-thick Al2O3 layer allows the study of the organic layer alone by isolating it from the ZnOr. A 5 nm-thick TiO2 however results in an interaction between the organic layer and ZnOr layer. Femtosecond absorption spectroscopy revealed that a 5 nm-thick TiO2 shell enables charge separation to occur between the organic and semiconductor materials. Dye sensitized solar cell experiments further validate that this TiO2 shell decreases charge recombination. A new type of graphene-alumina composite membrane was developed and mechanically assessed using the bulge test. The composite membrane is significantly more robust than plain Al2O3, withstanding at least 3 times more differential pressure. Raman measurements indicated the graphene reinforcing layer remains undamaged after bulge testing despite cracking in the ALD layer.

Details

Original languageEnglish
QualificationDoctor's degree
Awarding Institution
Supervisors/Advisors
Publisher
  • Aalto University
Print ISBNs978-952-60-6236-5
Electronic ISBNs978-952-60-6237-2
Publication statusPublished - 2015
MoE publication typeG5 Doctoral dissertation (article)

    Research areas

  • atomic layer deposition, plasma enhanced atomic layer deposition, dry etching, AIN, Al2O3, AZO, TiO2, GaAs, graphene, nanowires, nanorods

ID: 18375682