1. III-V semiconductors present unique platforms to build devices ranging from
sensors to light emitting diodes. With the recent surge in organic thin film
technology, interfacing organic materials and III-V semiconductors presents
a challenge in terms of properties, methodology, stability, and sustainability.
Previous research yielded success in the form of a simultaneous etching
and functionalization process utilizing a diluted phosphoric acid and 1H, 1H,
2H, 2H-Perfluorooctane phosphonic acid (CF3(CF2)5(CH2)2PO(OH)2) –
PFOPA additive as seen in the figure below (bottom right). This method (see
left illustration) utilizes bench-top beaker chemistry to chemically bound self-
assembled molecules in a cost effective, environmentally benign,
reproducible, and scalable fashion. Earlier results with GaN indicate the
ability to modulate the surface potential (captured via kelvin probe force
microscopy-KPFM, top right) in addition to optical response (not shown).
Here we investigate the environmental stability of GaN and GaP with
various surface treatments that also include post-capping with hydrogen
peroxide as a means to differentiate corrosion mechanisms. This was
performed with inductively coupled plasma-mass spectrometry (ICP-MS) in
addition to surface properties via atomic force microscopy (AFM), water
contact angle, and X-ray photoelectron spectroscopy (XPS)
Comparison of the Environmental Stability of Functionalized Gallium Nitride
and Gallium Phosphide
Stewart Wilkins1, Tania Paskova1,2, Lewis Reynolds, Jr.1, Albena Ivanisevic1
1 Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695
2 Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695
Materials Science and Engineering
Representative qualitative
AFM topographic images (top)
identify pit coalescence on the
surface for GaN with little to
no features on GaP.
Quantitative analysis of the
RMS surface roughness
indicated no significant
(accounting for standard
deviation) variance between
various treatments and post
processing steps. This
followed previous results, with
the differences being
distinguishable only with
KPFM (introduction figure, top
right). Water contact angle
relied more on the surface
chemistry and produced
unique signatures, particularly
for PFOPA treated GaP, which
demonstrated more uniform
surface coverage than PFOPA
on GaN (which tended to
agglomerate). Post soaking
hydration effects did not
survive intervals between
characterization sessions.
Polar Bulk Nonpolar Bulk
Etched
Nonpolar on Al2O3
1. Pearce, B. L.; Wilkins, S. J.; Paskova, T.; Ivanisevic, A.; J. Mat. Res., 2015, Accepted.
2. Wilkins, S. J.; Slomski, M. J.; Paskova, T.; Weyher, J. L.; Ivanisevic, A.; App. Phys. Lttrs.,
2015, Accepted.
3. Wilkins, S. J.; Paskova, T.; Reynolds, Jr., C. L.; Ivanisevic, A.; ChemPhysChem, 2015,
Accepted.
4. Wilkins, S. J.; Paskova, T.; Ivanisevic, A.; J. App. Phys., 2013, 114, 064907-1-7.
5. Wilkins, S. J.; Paskova, T.; Ivanisevic, A.; App. Surf. Sci., 2015, 327, 498-503.
6. Wilkins, S. J.; Greenough, M.; Arellano, C.; Paskova, T.; Ivanisevic, A.; Langmuir, 2014,
30, 2038-2046.
7. Wilkins, S. J.; Paskova, T.; Ivanisevic, A.; App. Surf. Sci., 2014, 295, 207-213.
Etched
The figures above (left, middle) show Ga 2p3/2 peaks for given treatments, which are shown due to
their surface sensitivity to oxide formation. GaN (left) and GaP (middle) exhibit increased gallium
sub-oxide and oxide formation for treatments capped with hydrogen peroxide prior to soaking (a).
Post soaking (b) repeats this whereas GaP is not as apparent. Additionally, the P2p region (top
right) for GaP indicates increased phosphorous oxide formation, particularly after soaking. To
confirm bonding, the F1s spectra (bottom right) indicates PFOPA presence post functionalization.
Introduction and Objective
Methods
Surface Chemistry
References
The use of simultaneous etching and functionalization provides a
economical and greener approach to modulating the surface properties
and aqueous environmental stability profiles of GaN and GaP. The
addition of hydrogen peroxide highlighted differences in the inherent
stabilities of GaN vs. GaP as well as the effect (as low as 8% and as
high as 145% between hydrogen peroxide capping) surface chemistry
has on the treated material.
Conclusions
Functionalization was performed using a diluted phosphoric acid or a diluted
phosphoric acid etchant with a 1.5 mM PFOPA additive as seen from the
figure below (left). Following functionalization, a series of samples underwent
additional capping via diluted hydrogen peroxide. The samples used were
bulk-free standing polar GaN and silicon bound polar GaP as seen in the X-
ray diffraction (XRD) below (right). To test aqueous stability, samples were
soaked for a week between characterization intervals.
Surface Topography
Solution Stability
The figures above show the resulting gallium content leached per area (left) after 1 week of
soaking in addition to Pourbaix diagrams (right) illustrating the soluble components of GaP and
GaN respectively. Leaching is attributed to the formation of oxide complex dissociation and
subsequent soluble species encouraged by hydrogen peroxide post-processing.
Functionalization
and Etchant Bath
1. Solvent Clean
2. Etch to Remove Oxide
1. Remove Physisorbed
Adsorbate
2. Characterize