Passivation of III–V Nanowires Using Dielectrics Deposited by Atomic Layer Deposition
type: CreativeWork
description: III–V semiconductor nanowires have many uses in (opto)electronic applications including infrared photodetectors and photovoltaic cells [1], tunnelling field-effect transistors (TFETs) [2] and high-frequency transistors [ 3]. Indium arsenide (InAs) is of interest as it has a direct narrow band gap of 0.36 eV at 300 K and 0.40 eV at 77 K [4], an electron affinity around 4.9 eV [ 4] and high electron mobilities ranging from 20,000 and 60,000 cm² V¯¹ s¯¹ at temperatures of 300 and 77 K respectively [4]. Nanowires (NWs) feature high surface area-to-volume ratios, and consequently their optical and electrical properties are strongly affected by surface states [5]. Furthermore, the native oxide on InAs NWs contains trap sites for electrons and their energies lie in the InAs conduction band. Therefore, controlling the electrical characteristics of these III–V NWs via surface passivation and encapsulation will be essential for their adoption into commercial applications. This thesis investigates surface passivation of InAs nanowire field-effect transistors (NWFETs) using alumina dielectric layers [6]. Passivation refers to the removal of the native oxide which contains charge carrier traps sites using trymethyl aluminium [6, 7] and removing dangling bonds using ammonium sulphide [8,9]. Alumina was deposited by atomic layer deposition (ALD) using trimethylaluminium (TMA) as the aluminium precursor and H₂O or oxygen plasma as the oxygen sources. NWFETs were encapsulated with alumina over a range of deposition temperatures from 85 to 300 °C and a range of layer thicknesses from 3 to 50 nm. The alumina was deposited using both plasma-enhanced and thermal ALD methods. The electrical characteristics measured include field-effect mobility, on/off current ratio, forward and backward threshold voltage and hysteresis. The quality of the alumina that encapsulated the devices was determined by the refractive index and growth rate per ALD cycle using imaging ellipsometry. In all cases wh…
abstract: III–V semiconductor nanowires have many uses in (opto)electronic applications including infrared photodetectors and photovoltaic cells [1], tunnelling field-effect transistors (TFETs) [2] and high-frequency transistors [ 3]. Indium arsenide (InAs) is of interest as it has a direct narrow band gap of 0.36 eV at 300 K and 0.40 eV at 77 K [4], an electron affinity around 4.9 eV [ 4] and high electron mobilities ranging from 20,000 and 60,000 cm² V¯¹ s¯¹ at temperatures of 300 and 77 K respectively [4]. Nanowires (NWs) feature high surface area-to-volume ratios, and consequently their optical and electrical properties are strongly affected by surface states [5]. Furthermore, the native oxide on InAs NWs contains trap sites for electrons and their energies lie in the InAs conduction band. Therefore, controlling the electrical characteristics of these III–V NWs via surface passivation and encapsulation will be essential for their adoption into commercial applications. This thesis investigates surface passivation of InAs nanowire field-effect transistors (NWFETs) using alumina dielectric layers [6]. Passivation refers to the removal of the native oxide which contains charge carrier traps sites using trymethyl aluminium [6, 7] and removing dangling bonds using ammonium sulphide [8,9]. Alumina was deposited by atomic layer deposition (ALD) using trimethylaluminium (TMA) as the aluminium precursor and H₂O or oxygen plasma as the oxygen sources. NWFETs were encapsulated with alumina over a range of deposition temperatures from 85 to 300 °C and a range of layer thicknesses from 3 to 50 nm. The alumina was deposited using both plasma-enhanced and thermal ALD methods. The electrical characteristics measured include field-effect mobility, on/off current ratio, forward and backward threshold voltage and hysteresis. The quality of the alumina that encapsulated the devices was determined by the refractive index and growth rate per ALD cycle using imaging ellipsometry. In all cases wh…
author: O Riada, Colm
language: eng
keywords: ALD, alumina, deposition, dielectric, InAs, indium arsenide, Nanowire, NWFET, passivation, temperature, Transistor
license: https://www.repository.cam.ac.uk/bitstreams/9d73904b-0bfb-43c6-a1b9-5d31143e77eb/download
license: http://purl.org/NET/rdflicense/allrightsreserved
date published: 2025-02-18
date modified: 2026-07-22T22:24:25Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.126387