Detection of an unintentional Si doping gradient in site-controlled GaN nanowires grown using a Si3N4 mask by spatially resolved cathodoluminescence and Raman spectroscopy
Mikel Gómez Ruiz,
Matt D. Brubaker,
Kris A. Bertness,
Alexana Roshko,
Hans Tornatzky,
Manfred Ramsteiner,
Oliver Brandt,
Jonas Lähnemann
Affiliations
Mikel Gómez Ruiz
Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5–7, D-10117 Berlin, Germany
Matt D. Brubaker
National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
Kris A. Bertness
National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
Alexana Roshko
National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
Hans Tornatzky
Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5–7, D-10117 Berlin, Germany
Manfred Ramsteiner
Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5–7, D-10117 Berlin, Germany
Oliver Brandt
Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5–7, D-10117 Berlin, Germany
Jonas Lähnemann
Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5–7, D-10117 Berlin, Germany
Highly uniform arrays of site-controlled GaN nanowires are synthesized by selective area growth using a Si3N4 mask and molecular beam epitaxy. Systematic modulation of the emission along the nanowire axis is observed in spectrally resolved cathodoluminescence linescans. We show that this intensity change is an indicator of unintentional Si incorporation during growth resulting from the interaction between the impinging Ga atoms and the mask material. The gradual reduction of the cathodoluminescence intensity along the nanowire highlights the important role of the growth geometry within the synthesis reactor, with shadowing from the elongating nanowires inhibiting the reaction with the mask. This gradient in Si doping is confirmed by the quenching of the longitudinal optical phonon line measured in Raman spectra along the nanowire axis. The corresponding carrier density is derived from the frequency of the coupled phonon–plasmon mode. The spectroscopic identification of inversion domain boundaries in the majority of the nanowires is also attributed to the Si incorporation. From temperature dependent cathodoluminescence experiments, we derive the activation energy for excitons bound to these defects.
