Origin of Strong Photoluminescence Polarization in GaNP Nanowires

Abstract

The III–V semiconductor nanowires (NWs) have a great potential for applications in a variety of future electronic and photonic devices with enhanced functionality. In this work, we employ polarization-resolved microphotoluminescence (μ-PL) spectroscopy to study polarization properties of light emissions from individual GaNP and GaP/GaNP core/shell NWs with average diameters ranging between 100 and 350 nm. We show that the near-band-edge emission, which originates from the GaNP regions of the NWs, is strongly polarized (up to 60% at 150 K) in the direction perpendicular to the NW axis. The polarization anisotropy can be retained up to room temperature. This polarization behavior, which is unusual for zinc blende NWs, is attributed to local strain in the vicinity of the N-related centers participating in the radiative recombination and to preferential alignment of their principal axis along the growth direction. Our findings therefore show that defect engineering via alloying with nitrogen provides an additional degree of freedom to tailor the polarization anisotropy of III–V nanowires, which is advantageous for their applications as nanoscale emitters of polarized light.

Raman spectroscopy of GaP/GaNP core/shell nanowires

“…None of these mechanisms, however, seem to be relevant to the studied structures. Indeed, according to our previous SEM and TEM studies, 12 the NWs are uniform in diameter and show faceting on the scale of 5 nm, which is by far smaller than the experimentally determined k SO . Instead, the momentum of the activated mode could correspond to the momentum transferred to the NW upon back scattering of the excitation light, i.e., q ¼ 4p ffi ffi e p k exc ¼ 0:060 nm À1 which is very close to the determined value of q SO .…”

“…The characteristic wavelength of the perturbation of the surface potential that activated the Raman scattering process is also determined as being 115 nm. Based on our previous TEM studies, 12 the calculated value does not correlate with neither diameter modulation nor surface roughness. The activation of these phonon modes is, therefore, tentatively attributed to resonant Raman scattering via defect states, e.g., due to point defects or structural defects located in the vicinity to the NW surfaces.…”

“…8 A promising material system attractive for applications in solar cells and light-emitting diodes is GaN x P 1-x / GaN y P 1-y core/shell NWs. [9][10][11][12] Incorporation of several percent of nitrogen in gallium phosphide reduces its lattice constant, thereby minimizing lattice mismatch with Si. 13 Also, a strong interaction between the N-related localized states and the extended states of GaP modifies the band structure of the forming alloy leading to an increased oscillator strength of the band-to-band optical transitions [14][15][16] and a splitting of the conduction band states into two subbands.…”

“…According to highresolution transmission electron microscopy (HRTEM), both GaP and GaP/GaNP core/shell NWs predominantly have the ZB structure with a rather high density of random twins/ stacking faults perpendicular to the growth axis. 12 The contribution of the hexagonal WZ phase in a single NW was typically below 5% of the whole volume. For a comparison, a 750-nm-thick GaN 0.009 P 0.991 epilayer grown by gas-source a)…”

“…This formation of micro facets in the investigated NWs was confirmed from the performed TEM measurements. 12 As to the TO* mode, it has the highest intensity in the x(z,z)x configuration, i.e., it does not follow the selection rules for WZ. 23 Moreover, a comparison of the Raman spectra presented in Figs.…”