Cross-sectional and plan-view cathodoluminescence of GaN partially coalesced above a nanocolumn array

Abstract

The optical properties of GaN layers coalesced above an array of nanocolumns have important consequences for advanced optoelectronic devices. GaN nanocolumns coalesced using a nanoscale epitaxial overgrowth technique have been investigated by high resolution cathodoluminescence (CL) hyperspectral imaging. Plan-view microscopy reveals partially coalesced GaN layers with a sub-μm scale domain structure and distinct grain boundaries, which is mapped using CL spectroscopy showing high strain at the grain boundaries. Cross-sectional areas spanning the partially coalesced GaN and underlying nanocolumns are mapped using CL, revealing that the GaN bandedge peak shifts by about 25 meV across the partially coalesced layer of ∼2 μm thick. The GaN above the nanocolumns remains under tensile strain, probably due to Si out-diffusion from the mask or substrate. The cross-sectional data show how this strain is reduced towards the surface of the partially coalesced layer, possibly due to misalignment between adjacent partially coalesced regions

Luminescence associated with stacking faults in GaN

“…Consequently, it is likely that so far not clearly identified emission energies observed in similar structures are also related to BSFs or cubic segments. Notably, an emission peak at 3.4 eV was observed in [94] and ascribed to the N polarity of the sample, emission lines at 3.32 and 3.42 eV in [95] were attributed to the Y2 and Y6 defect peaks [65], and a room temperature luminescence peak at 3.19 eV in [96] was attributed to the donor-acceptor pair transition. Also, the emission band at 3.40-3.42 eV related to defects close to the nanowire substrate interface in [97] is likely related to I 1 BSFs.…”

Characteristics of GaN-based light emitting diodes with different thicknesses of buffer layer grown by HVPE and MOCVD

“…In addition, the average peak intensities of the 10 μm × 10 μm area are ∼1.6 × 10 4 counts/eV and ∼2.4 × 10 4 counts/eV for the 12 μm and 30 μm samples, respectively, which is consistent with the difference in dislocation density. In figures 2(b) and (d), the CL peak energy varies slightly across the scanned areas; however, when the buffer thickness increases from 12 μm to 30 μm, a red shift in the GaN peak energy can be observed which indicates that the compressive strain induced by the mismatch of lattice constants and different thermal expansion coefficients between GaN layers and sapphire substrates was relaxed [22,23].…”

Bias dependence and correlation of the cathodoluminescence and electron beam induced current from an InGaN/GaN light emitting diode

“…CL hyperspectral imaging-the recording of a full spectrum at each pixel in a scan-has proven to be of significant use in mapping and correlating variations in the spectral emission parameters of epilayers, 2,3 multiquantum well (MQW) heterostructures, 4 and optoelectronic nanostructures. [5][6][7] However, luminescence is just one of the many consequences of the interaction of the electron beam with the material. If the device under excitation is connected to a closed circuit, a portion of the generated charge carriers can escape the material and be measured as the electron beam induced current (EBIC), provided there is a driving force in the circuit.…”