TY - JOUR
T1 - The role of surface depletion layer effects on the enhancement of the UV emission in ZnO induced by a nanostructured Al surface coating
AU - Fiedler, Saskia
AU - Lee Cheong Lem, Laurent O.
AU - Ton-That, Cuong
AU - Phillips, Matthew R.
N1 - Publisher Copyright:
© 2019
PY - 2020/2/28
Y1 - 2020/2/28
N2 - The UV enhancement of Al-coated ZnO single crystals with a wide range of carrier densities is systematically studied using depth-resolved cathodoluminescence and photoluminescence as well as valence band X-ray photoemission spectroscopy (VB-XPS). An up to 17-fold enhanced PL UV emission for Al-coated ZnO with the highest carrier density was measured, which falls to a 12-fold increase for the lowest carrier density. Depth-resolved cathodoluminescence measurements confirm that the enhancement is strongest near the Al-ZnO interface consistent with an increased UV emission due to an exciton-localized surface plasmon coupling mechanism. Correlative cathodoluminescence, photoluminescence and VB-XPS studies reveal that a number of additional effects related to the presence of the Al surface coating also contribute to the UV enhancement factor. These include increased UV enhancement due to the formation of a surface depletion layer induced by the Al coating, which also passivates competitive non-radiative surface recombination channels found in uncoated ZnO. Significantly, it was established that the magnitude of the emission enhancement factor can be raised in a controlled way by reducing the thickness of the depletion layer by increasing the carrier density. The contribution of these effects collectively provides an explanation for the large span of enhancement factors reported in the literature.
AB - The UV enhancement of Al-coated ZnO single crystals with a wide range of carrier densities is systematically studied using depth-resolved cathodoluminescence and photoluminescence as well as valence band X-ray photoemission spectroscopy (VB-XPS). An up to 17-fold enhanced PL UV emission for Al-coated ZnO with the highest carrier density was measured, which falls to a 12-fold increase for the lowest carrier density. Depth-resolved cathodoluminescence measurements confirm that the enhancement is strongest near the Al-ZnO interface consistent with an increased UV emission due to an exciton-localized surface plasmon coupling mechanism. Correlative cathodoluminescence, photoluminescence and VB-XPS studies reveal that a number of additional effects related to the presence of the Al surface coating also contribute to the UV enhancement factor. These include increased UV enhancement due to the formation of a surface depletion layer induced by the Al coating, which also passivates competitive non-radiative surface recombination channels found in uncoated ZnO. Significantly, it was established that the magnitude of the emission enhancement factor can be raised in a controlled way by reducing the thickness of the depletion layer by increasing the carrier density. The contribution of these effects collectively provides an explanation for the large span of enhancement factors reported in the literature.
KW - Aluminum nanoparticles
KW - Cathodoluminescence
KW - Localized surface plasmons
KW - Photoluminescence
KW - UV enhancement
KW - ZnO
UR - http://www.scopus.com/inward/record.url?scp=85074800923&partnerID=8YFLogxK
U2 - 10.1016/j.apsusc.2019.144409
DO - 10.1016/j.apsusc.2019.144409
M3 - Article
SN - 0169-4332
VL - 504
JO - Applied Surface Science
JF - Applied Surface Science
M1 - 144409
ER -