Laser‐assisted atom probe tomography of MBE grown GaN nanowire heterostructures

Abstract

AbstractLaser‐assisted atom probe tomography (L‐APT) was performed on GaN nanowires (NWs) and axial GaN/InGaN nanowire heterostructures. All samples were grown by MBE on Si(111) substrates. The laser pulse energy (PE) at 355 nm used in L‐APT analysis of GaN NWs was restricted to the range of 2‐50 fJ in order to recover the correct GaN stoichiometry within experimental uncertainty. Higher PE at 355 nm generally returns an apparent (but unphysical) deficit in N composition for GaN. Axial GaN/InGaN NW heterostructures were also grown by MBE. In these experiments a GaN NW segment was first grown at 820 °C followed by GaN‐capped InGaN marker layers grown variously at 585 and 615 °C. The capped InGaN markers were separated by GaN spacer layers. L‐APT revealed that under certain growth conditions, In diffused throughout the quantum well region. These observations were corroborated by HRTEM. Moreover, L‐APT performed on the GaN/InGaN NWs with PE = 2 fJ revealed that regions with dispersed In showed an (unphysical) N deficit but regions where the InGaN marker layers remained localized showed the approximately correct stoichiometry. Interestingly, even when the In markers remain localized, background In is still found in the GaN spacers between the markers. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)