Multimicroscopy of cross-section zincblende GaN LED heterostructure

Zincblende GaN has the potential to bridge the green gap due to the absence of internal electric fields with respect to wurtzite GaN. However, at present, the quality of zincblende GaN light emitting diodes (LEDs) is not yet sufficient for useful efficient green devices. One of the major challenges is the poor spectral purity of the emitted light. A multimicroscopy approach, combining scanning electron microscopy-cathodoluminescence (SEM-CL), scanning transmission electron microscopy (STEM), and scanning electron diffraction (SED), is applied on a single feature to enable cross correlation between techniques and to investigate the possible causes for the broad optical emission of a zincblende GaN LED structure. This investigation demonstrates that SEM-CL on a site-specific TEM cross section prepared by focused ion beam (FIB) microscope can provide access to nanoscale light emission variations that can be directly related to structural differences seen in STEM. We demonstrate that the general large quantum well (QW) emission peak width relates to quantum well thickness and In content fluctuations. Multiple low-energy QW emission peaks are found to be linked with stacking fault bunches that intersect the QWs. Splitting of the QW emission peak is also found to be caused by the formation of wurtzite-phase inclusions associated with twins formed within the zincblende matrix. Our characterization also illustrates the quantum well structure within such wurtzite inclusions and their impact on the optical emission.& nbsp;& nbsp;(C) 2021 Author(s).

Automated summary

The study investigates the broad optical emission of zincblende GaN LED structures, attributing it to factors such as quantum well thickness and In content fluctuations, the relationship between stacking fault bunches and low-energy QW emission peaks, and the formation of wurtzite-phase inclusions. The multimicroscopy approach reveals nanoscale variations related to these factors and provides insights into the structural differences affecting the emission characteristics.