eprintid: 23869
rev_number: 8
eprint_status: archive
userid: 3506
dir: disk0/00/02/38/69
datestamp: 2018-01-04 08:26:22
lastmod: 2018-01-17 14:04:55
status_changed: 2018-01-04 08:26:22
type: doctoralThesis
succeeds: 23868
metadata_visibility: show
creators_name: Hietzschold, Sebastian
title: Surface Functionalization of Nickel Oxide and Gallium Nitride for Hybrid Opto-Electronics
subjects: 530
divisions: 130700
adv_faculty: af-13
abstract: This thesis examines the influence of surface functionalization
by self-assembled monolayers (SAMs) on two different materials, (i) nickel
oxide and (ii) gallium nitride.
(i) Thin solution-processed films of nickel oxide (sNiO) were modified with
dipolar self-assembled monolayers of 4-cyanophenyl-phosphonic acid (CYNOPPA)
to improve the energy level alignment and the chemical compatibility to the donor
in F4ZnPc:C60 organic photovoltaic devices. A detailed analysis of infrared and
photoelectron spectroscopy showed the chemisorption of the molecules with a
nominal layer thickness of around one monolayer. The spectroscopic results gave
further insight into the chemical composition of the SAM. Density functional theory
calculations were employed to reveal energetically allowed binding configurations of
the phosphonate anchor group. CYNOPPA successfully increased the work function
of the sNiO up to 5.1-5.2 eV, leading to a well-matched Fermi level of the hole-contact
layer to the ionization potential of the donor. Unexpectedly, the improved alignment
did not lead to a higher power conversion efficiency. Instead, a significant reduction
of the fill factor was observed, which was assigned to the formation of a transport
barrier due to a low conductive interface region. However, it was shown that the
barrier can be reduced by doping the oxide hole-contact layer and thereby increase
its charge carrier density.
(ii) For the goal of GaN nanowire surface state passivation and control of the corresponding
band bending, different GaN planes were functionalized with self-assembled
monolayers. A step-by-step procedure of solvent cleaning, plasma treatment and
HCl etching was developed to guarantee clean surfaces for SAM growth. X-ray
photoelectron spectroscopy (XPS) measurements showed that oxygen as well as
carbon contents could be reduced to a minimum with this procedure. SAM precursor
with different anchoring groups were tested to find the best binding partner for
the GaN surface. The SAM quality and passivation functionality was determined
by Kelvin probe surface photovoltage and contact angle measurements. It was
shown that amines and thiols suffer from low surface coverage on GaN(0001) under
ambient conditions. Hence, an oxide template layer was grown for the attachment
of phosphonic acids (PAs). Two phosphonic acids with different intrinsic dipole
moments were applied to oxidized high quality GaN(0001) and GaN(1100) surfaces
grown by molecular beam epitaxy. XPS and contact angle measurements revealed
dense monolayer coverage of the PA-SAMs. Despite the oxide buffer layer, the band
bending of the GaN was reduced by the chemisorption and molecular backbones of
the PAs. Continuous-wavelength photoluminescence (cw-PL) measurements showed
an increase of the total PL intensity, which suggests that a reduction of the band
bending is essential for high luminescence quantum yields.
date: 2017
id_scheme: DOI
id_number: 10.11588/heidok.00023869
ppn_swb: 1658675738
own_urn: urn:nbn:de:bsz:16-heidok-238693
date_accepted: 2017-12-13
advisor: HASH(0x564e1c40b3f0)
language: eng
bibsort: HIETZSCHOLSURFACEFUN2017
full_text_status: public
citation:   Hietzschold, Sebastian  (2017) Surface Functionalization of Nickel Oxide and Gallium Nitride for Hybrid Opto-Electronics.  [Dissertation]     
document_url: https://archiv.ub.uni-heidelberg.de/volltextserver/23869/1/2017_Dissertation_SebastianHietzschold.pdf