The
interaction of n-type GaN(0001) surfaces with potassium and
water is investigated using photoelectron spectroscopy, with special
focus on adsorbate–substrate charge-transfer processes and
water dissociation. Potassium atoms adsorb at the surface, forming
a distinct surface dipole layer. For very low K coverage, the attached
ionized K adsorbates result in a drop of the work function and the
released electrons induce a reduction of the initial upward band bending.
After stabilization of both quantities in the sub-monolayer regime,
a reverse effect is observed for higher K coverage up to one monolayer
(ML), exceeding the upward band bending of the clean surface. If the
K-covered surface is exposed to water, hydroxyl groups are formed,
whereas during long K and H2O coadsorption, a potassium
hydroxide film grows. In both cases, a further reduction of the work
function and an abrupt change in the surface depletion layer is recorded.
For the coadsorption, initially an electron accumulation layer forms
at the surface, approaching flat band conditions for higher KOH thickness.
Overall, the surface band bending can be drastically modified in the
range between +0.5 and −0.6 eV. These observations clearly
show that the electron density at the GaN(0001) surface can be reversibly
tuned by alkali-based adsorbates. Different reactions are observed,
which are directly linked to the charge-transfer processes and chemical
reactions induced by the K 4s electrons.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.