Charge carrier generation, relaxation, and recombination in polytypic GaAs nanowires studied by photoluminescence excitation spectroscopy

Abstract

We report results of a study of polytypic GaAs nanowires using low-temperature photoluminescence excitation spectroscopy. The nanowire ensemble shows a strong absorption at 1.517 eV, as a result of resonant generation of heavy-hole excitons in the zinc-blende segments of the nanowires. Excitons then diffuse along the length of the nanowire and are trapped by the type-II quantum discs arising from the zinc-blende/wurtzite crystal structure alternation and recombine radiatively. Finally, experiments on single nanowires demonstrate that the energy of the Γ7 conduction band to Γ9 valence band exciton of wurtzite GaAs is 1.521 eV at 4 K.

Strongly polarized quantum-dot-like light emitters embedded in GaAs/GaNAs core/shell nanowires

“…The PL spectra of the reference GaAs NWs are consistent with those previously reported in the literature. 18,[41][42][43][44][45][46][47][48][49] Within the pure ZB part (i.e. the ZB region of the wire with only a few twins), the PL emission is dominated by the free exciton (FX) transition at 1.515 eVsee Fig.…”

“…1a and e. Additionally, the PL spectra contain a series of lines within the spectral range of 1.44-1.47 eV that were previously shown to originate from type-II transitions at boundaries between the WZ and ZB phases and at stacking faults. 18,[41][42][43][44][45][46][47][48][49] The presence of the GaNAs shell results in a significant modification of the µ-PL spectrasee Fig. 2b.…”

Long exciton lifetimes in stacking-fault-free wurtzite GaAs nanowires

“…Indeed, the coupling between adjacent SFs can cause the formation of minibands with additional electronic states and thus modify the PL emission, as has already been detected in rotationally twinned InP NWs 29 and polytypic ZB/WZ GaAs NWs. 12,[17][18][19] Consequently, all the emission lines in Fig. 2(a) have energies smaller than the free exciton recombination in ZB GaAs (E ¼ 1.515 eV).…”

“…[7][8][9] The resulting optical characteristics and selection rules promise interesting properties for optical spin injection and might also open novel means of band structure engineering within single GaAs NWs through controlled ZB-WZ superlattices. 10 It is currently still challenging to reproducibly grow long NW segments of pure WZ phase 4,9,[11][12][13][14][15][16] as well as to control the switching of WZ to ZB, 3,[17][18][19] impeding the experimental exploration of the characteristic properties of pure and stacking-fault (SF)-free WZ GaAs and the validation of theoretical predictions. [7][8][9][12][13][14][15][16]20 In this letter, we investigate single GaAs NWs grown by molecular beam epitaxy (MBE) in successive microphotoluminescence (l-PL) spectroscopy and transmission electron microscopy (TEM) analyses of each wire.…”

Origin of radiative recombination and manifestations of localization effects in GaAs/GaNAs core/shell nanowires

“…Such emission spectrum is typical for GaAs NWs with mixed ZB and wurtzite WZ crystal structure and has been shown to arise from excitonic transitions at the interfaces between the WZ and ZB phases and at staking faults. [23][24][25][26] Formation of the GaNAs shell has several effects on the PL spectra. First, the core emission is substantially quenched, likely due to its absorption by the outer GaNAs shell with a lower bandgap and excitation transfer from the core to the shell layer.…”