Dynamics of stacking faults luminescence in GaN/Si nanowires

Abstract

Evidences are shown that excitons at stacking faults (SFs) in GaN nanowires (NWs) behave like 2-dimentional particles in quantum wells. The SFs were studied in samples of coalescent GaN nanowires grown on silicon substrate. They emit strong luminescence at room temperature what promises possible applications of SF for light emitting devices. At 4K, the NWs exhibit sharp near-bandgap luminescence with the strongest signal from donor-bound excitons (DX) at 3.471eV and from stacking faults (SF) at 3.42eV. Observations of the SF dynamics show spectral diffusion of energy in time (shift up to ΔEd=8meV) and S-shaped energy–temperature dependence. Both these features are often reported as characteristic for quantum wells.Moreover we report on two dynamical effects, which confirm two-dimensional character of excitons in SFs. First, decrease of radiative recombination rate at higher temperature rR =1/(αT+t0), shows that excitons have momentum. Second, the SF luminescence peak has an exponential slope, i.e. is similar to thermal distribution, which points to kinetic energy of the excitons. The effective temperature calculated from the shape of the SF peak was in the range of few tens of Kelvins. It decreased in time with the cooling time τC=0.37±0.05ns.