Nature of excitons bound to inversion domain boundaries: Origin of the 3.45-eV luminescence lines in spontaneously formed GaN nanowires on Si(111)

Abstract

We investigate the 3.45-eV luminescence band of spontaneously formed GaN nanowires on Si(111) by photoluminescence and cathodoluminescence spectroscopy. This band is found to be particularly prominent for samples synthesized at comparatively low temperatures. At the same time, these samples exhibit a peculiar morphology, namely, isolated long nanowires are interspersed within a dense matrix of short ones. Cathodoluminescence intensity maps reveal the 3.45-eV band to originate primarily from the long nanowires. Transmission electron microscopy shows that these long nanowires are either Ga polar and are joined by an inversion domain boundary with their short N-polar neighbors, or exhibit a Ga-polar core surrounded by a N-polar shell with a tubular inversion domain boundary at the core/shell interface. For samples grown at high temperatures, which exhibit a uniform nanowire morphology, the 3.45-eV band is also found to originate from particular nanowires in the ensemble and thus presumably from inversion domain boundaries stemming from the coexistence of Nand Ga-polar nanowires. For several of the investigated samples, the 3.45-eV band splits into a doublet. We demonstrate that the higher-energy component of this doublet arises from the recombination of two-dimensional excitons free to move in the plane of the inversion domain boundary. In contrast, the lower-energy component of the doublet originates from excitons localized in the plane of the inversion domain boundary. We propose that this in-plane localization is due to shallow donors in the vicinity of the inversion domain boundaries.

External control of GaN band bending using phosphonate self-assembled monolayers

“…In particular, the donor bound exciton (D 0 ,X A ) has a linewidth of 1.5 meV (4 meV) for the nanowire ensemble on Ti (Si). Transitions from excitons bound to stacking faults (SFs) [72] and inversion domain boundaries (IDBs) [73,74] are also detected, as typically reported for this type of nanostructures. Interestingly, we do not observe any spectral signature related to the deposition of PFOPA or OPA.…”

p-Type Doping of GaN Nanowires Characterized by Photoelectrochemical Measurements

“…This change could be related to the development with increasing T Mg of an additional line related to Mg and centered at 3.45 eV that actually dominates the PL spectrum for T Mg = 590 °C (a similar behavior was reported in ref for a p-doped GaN film). However, as a note of caution we point out that self-induced unintentionally doped GaN NWs often show an emission band around 3.45 eV, which arises from exciton recombination at inversion domain boundaries. , …”

“…However, as a note of caution we point out that self-induced unintentionally doped GaN NWs often show an emission band around 3.45 eV, which arises from exciton recombination at inversion domain boundaries. 52,53 Another indication of Mg incorporation is the observation of PL from donor−acceptor pairs (DAP). Figure 2b depicts the same spectra as seen in Figure 2a in a wider energy range.…”

Investigation of the effect of the doping order in GaN nanowire p–n junctions grown by molecular-beam epitaxy

“…Two additional lower intensity peaks around 3.45 eV and 3.42 eV were also observed. The former one at 3.45 eV is well-known for nominally undoped GaN NWs grown on Si substrates, which is usually assigned to be the excitonic recombination in presence of inversion domain boundaries [58,59]. The latter one at 3.42 eV can be associated with the recombination of excitons bound to plane stacking faults [60].…”