Open Access
Add to BibSonomy
Abstract
Nominal dopant-free zinc blende twinning superlattice InP nanowires have been grown with high crystal-quality and taper-free morphology. Here, we demonstrate its superior optical performance and clarify the different carrier recombination mechanisms at different temperatures using a time resolved photoluminescence study. The existence of regular twin planes and lateral overgrowth do not significantly increase the defect density. At room temperature, the as-grown InP nanowires have a strong emission at 1.348 eV and long minority carrier lifetime (∼3 ns). The carrier recombination dynamics is mainly dominated by nonradiative recombination due to surface trapping states; a wet chemical etch to reduce the surface trapping density thus boosts the emission intensity and increases the carrier lifetime to 7.1 ns. This nonradiative recombination mechanism dominates for temperatures above 155 K, and the carrier lifetime decreases with increasing temperature. However, radiative recombination dominates the carrier dynamics at temperature below ∼75 K, and a strong donor-bound exciton emission with a narrow emission linewidth of 4.5 meV is observed. Consequently, carrier lifetime increases with temperature. By revealing carrier recombination mechanisms over the temperature range 10-300 K, we demonstrate the attraction of using InP nanostructure for photonics and optoelectronic applications.
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
III-V semiconductor nanowire research has gained great success during the past decade in both the fundamental science and the different application fields [1]. InP, as a typical III-V semiconductor, pose advantages such as low surface recombination velocity (SRV) [2], low toxicity [3] and superior optical quality [4], thus InP nanowire has been extensively investigated for applications such as photovoltaics [5,6], photo-catalysis [7], optoelectronics [8–10], photonics [11], neuron science [12] and quantum science [13,14]. These applications require the development of InP nanowire growth to achieve the required structure and properties specific to each application. To date, InP nanowires with pure wurtzite (WZ) phase have been synthesized via the selective area epitaxy (SAE) method [4,15]. However, the development of zincblende (ZB) InP nanowires is much slower. The highest crystal quality for ZB (111)-orientated InP nanowires are twinning superlattice (TSL) structures formed by either adding a dopant [16], tuning the growth parameters [17,18] or controlling the Au droplet diameter [19]. The existence of rotational twin planes acts as planar defects in ZB structure, typically reducing the photoluminescence efficiency [20] and impairing mechanical properties [21]. The optical properties of InP TSL nanowire have been carefully studied by Vu et al. [19]. In their work, lateral overgrowth introduced a higher density of impurity in the shell and impurity related emission was observed at low temperatures, thus in-situ etching in needed to suppress the lateral growth [19].
In general, the high surface-to-volume ratio in the nanowire geometry leads to the facet surface playing a key role in emission efficiency. Despite the low SRV of InP [2], surface passivation using a dielectric layer such as POx/Al2O3 [22] have been shown to improve emission intensity, carrier lifetime and device performance. On the other hand, in intrinsic InP nanowires, pump-probe experiments have shown only a weak influence of surface states on carrier recombination [23]. This discrepancy in carrier recombination processes suggests our understanding of carrier dynamics in InP nanowires is still limited, particularly for nominal undoped InP TSL nanowires where it shows a superior optical quality.
Here, we use a combination of micro-photoluminescence (μ-PL), time-resolved photoluminescence (TRPL) and temperature-dependent PL to study the optical emission and carrier dynamics of high-quality nominal undoped ZB InP TSL nanowires. Our InP TSL nanowires show a carrier lifetime (τ) of up to 7.1 ns at room temperature after wet chemical etching, and a well-defined donor-bound exciton emission (1.411 eV) at 10 K with an emission linewidth of 4.6 meV. Surface states act as non-radiative recombination trapping center, limiting emission efficiency at room temperature. At low temperature, carrier recombination is dominated by radiative recombination of bound excitons, leading to an increase of carrier lifetime with temperature.
2. Experimental
InP TSL nanowire growth was performed via Au seeded vapor-liquid-solid approach in a metalorganic chemical vapor deposition (MOCVD) reactor running at 100 mbar. Before growth, Au colloidal particles with diameter of ∼30 nm were deposited on clean InP(111)B substrates. Then, these Au functionalized InP(111)B substrate pieces were loaded in to reactor for InP TSL nanowire growth. Nanowires were nucleated at a lower temperature (450 °C) for 5 min before ramping up to a higher growth temperature (600 °C) for one hour. During the growth, trimethylindium (TMIn) and phosphine (PH3) flow were kept at 0.8×10−5 and 8.93×10−3 mol/min, respectively. Highly purified H2 gas was used as the carrier gas with total gas flow rate of 15 liters per minute. The InP TSL nanowire growth conditions are similar to our previous work [17]. After growth, the morphology and crystal structure were measured by scanning electron microscopy (SEM) and transmission electron microscopy (TEM, JEOL2100F), respectively. For surface chemical treatment, the InP nanowires were first transferred by mechanically scraping the InP substrate using marked Si/SiO2 pieces. These transferred nanowires were dipped into ammonia fluoride diluted commercial hydrofluoric acid (BHF 45:1) or diluted HF (1:45) for 50 s, before washing with DI water. All the optical properties of single nanowire were characterized using a home built micro-PL system. Linearly polarized pulsed laser excitation (at 522 nm) with a pulse duration of ∼300 fs and a repetition rate of 20.8 MHz was focused on the middle section of single nanowire through a 100x/60x objective lens at room temperature (low temperature). The average laser power of 1 mW corresponds to a pulse energy of 48 pJ at room temperature. Single nanowire TRPL was measured using a Si single photon avalanche diode (SPAD) with time-correlated single photon counting (TCSPC) provided by a PicoHarp 300 system with a time-resolution of around 70 ps. A liquid helium-cooled cryostat adapted to the micro-PL platform was used for temperature dependent PL experiments where a long working distance objective lens (60×) was used. The details and fundamental of transient PL spectroscopy is well explained by Atallah et al. [24]. Here, transient PL is measured from single nanowires using a 400 nm laser excitation in a quasi-confocal microscopy arrangement. The emitted light was collected using a single mode optical fiber and directed to a two-channel folded Mach-Zender interferometer equipped with two silicon-SPAD detectors. The time-resolved spectra were calculated by time-binning the emitted light and performing a Fourier analysis of the differential signal as a function of path length difference.
3. Results and discussions
The morphology of the InP nanowires is shown in Fig. 1(a-b). Nanowires grow vertically with a wide distribution of length and diameter. For the typical long nanowires studied in this work, the length is 8 ± 1.5 μm with a diameter of 215 ± 31 nm which is much larger than the size (30 nm) of the Au colloids. It is interesting to note the high lateral growth rate does not lead to a tapered morphology, which is explained as a facet transformation from {111}A/B to stable and non-polar {110} facets [25]. High-resolution SEM image (see Fig. 1(b)) of the nanowire shows a zigzag morphology, indicating the existence of regular rotational twin planes. TEM image together with the inset selective area diffraction pattern (SADP) in Fig. 1(c) confirms that the InP nanowire has a ZB structure with periodical twin planes. These periodical twin planes cover nearly the whole nanowire except for the bottom and tip of the nanowire due to local growth condition fluctuation. Figure 1(d) shows a strong photoluminescence emission peak at room temperature under excitation power density of 560 W/cm2 and integration time of 1 second, which is comparable to those used on the high quality WZ InP nanowire grown by SAE method [4]. These results indicate that the rotational twin planes do not appear to impact the emission efficiency, agreeing with previous optical characterization of InP TSL nanowires [19]. The emission peak energy is comparable with that expected from planar ZB InP, with a peak at 1.348 eV and a full width at half maximum (FWHM) of 46 meV. No additional peaks are observed in the excitation power regime.
Fig. 1. Structural and optical properties of InP TSL nanowires. (a) Tilted SEM images of the InP TSL nanowires with (b) a magnified image showing the zigzag morphology. (c) Low magnification TEM image together with the corresponding SADP along the [1$\overline{1}$0] zone axis showing the ZB TSL structure. (d) Room temperature micro-PL spectra at different excitation powers together with (e) the corresponding carrier decay spectra.
TRPL measured at the emission peak are shown in Fig. 1(e). The photoluminescence decay can be well fitted with a bi-exponential decay and the carrier decay curves stay nearly the same under different excitation fluence. The minority carrier lifetime (τmc) in III-V semiconductor can be defined as: $1/{\tau _{mc}} = 1/{\tau _{nr}} + 1/{\tau _r}$, where τnr and τr represent the nonradiative and radiative lifetime, respectively. For InP nanowires, normally the carrier lifetime is dominated by τnr at room temperature. Consequently, the carrier decay would not change with increasing of excitation power, which agree with our experiments. The bi-exponential fitting results in larger errors on the fitted values since more fitting parameters are used. The extracted carrier lifetime for the fast and slow decay process is 1 ± 0.1 ns and 3.4 ± 0.7 ns, respectively. Even the fast decay lifetime is comparable to defect-free WZ InP nanowires grown by the selective area method [4], again showing the high optical quality of the fabricated InP TSL nanowires. Usually if the carrier decay is limited by defects, the carrier decay would present an exponential decay shape, which is in contradiction to our experiments. This bi-exponential carrier decay is also frequently observed in III-V semiconductor nanowires [26,27], suggesting that there are multiple carrier trapping mechanisms occurring during the carrier decay process. Identifying these trapping processes is typically challenging, since it can be caused by quite a few reasons. First, a fast decay component may be related to Auger recombination [28]. This situation is ruled out because it would lead to faster radiative recombination under higher carrier density. Secondly, the nanowires may contain inhomogeneous planar defect/polytype distribution. However, this is not observed during our TEM studies. Thirdly, there exists a combination of free-carrier and trap-assisted recombination. However, this situation leads to two features in the emission spectrum which is not observed here. Fourthly, the InP nanowires contains different types of trap states, which are responsible for the fast and slow charge trapping, respectively. This explains the excitation independent bi-exponential decay behavior of our InP nanowires, which is also observed in recent published TRPL study on in-situ HCl etched InP nanowires [27]. Based on the above analysis, we propose that the carrier recombination dynamics in our ZB InP TSL nanowires at room temperature is governed by non-radiative recombination, which agree with InP nanowires grown at 440 °C [27], InP nanowire array grown by SAE method [22], but is contradiction to intrinsic InP nanowires grown at 390 °C [23].
In our InP TSL nanowires, the nonradiative carrier trapping centers could be rotational twin planes, surface states or point defects. To determine whether the trapping centers are located at the surface, the as-grown InP TSL nanowires were chemically etched by diluted HF (or BHF) to reduce the surface state density without damaging its crystal quality. TEM images in Fig. 2(a-b) compare the crystal structure and surface before and after chemical treatment. Chemical treatment does not alter the crystal quality of the InP TSL nanowires, only reducing the thickness of the amorphous layer around the nanowire. This suggests that the wet chemical treatment could be helpful to clean/passivate the nanowire surface, as demonstrated by the PL and TRPL experiments comparison in Fig. 2(c-d). The photon emission intensity is enhanced and the photoluminescence decay is slower although the previously observed bi-exponential decay characteristic is still evident. The fast decay process (τ1) is nearly unchanged while the lifetime of the slow decay process (τ2) increases substantially to 7.1 ns, indicating that the fast component is not related to surface trapping but the slow component is. Taking the surface recombination into consideration, ${\tau _{mc}}$ can be written as: ${\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 {{\tau_{mc}}}}} \right.}\!\lower0.7ex\hbox{${{\tau _{mc}}}$}} = {\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 {{\tau_b}}}} \right.}\!\lower0.7ex\hbox{${{\tau _b}}$}} + {\raise0.7ex\hbox{${4S}$} \!\mathord{\left/ {\vphantom {{4S} d}} \right.}\!\lower0.7ex\hbox{$d$}}$ [29], where $\tau_{b}$, S and d represent bulk minority carrier lifetime, surface recombination velocity and nanowire diameter, respectively. The obtained diameter of the TSL nanowires is quite close to each other. Thus, we are not able to get the SRV data by comparing the lifetime at different diameters [4]. By assuming all non-radiative recombination happens at the nanowire surface, the bulk minority carrier lifetime contribution could be ignored and an upper limit for the SRV (Smax) can be then calculated by ${\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 {{\tau_{mc}}}}} \right.}\!\lower0.7ex\hbox{${{\tau _{mc}}}$}} = {\raise0.7ex\hbox{${4{S_{max}}}$} \!\mathord{\left/ {\vphantom {{4{S_{max}}} d}} \right.}\!\lower0.7ex\hbox{$d$}}$. Since the surface chemical treatment only effect τ2, τ2 is used to calculate the Smax in our nanowire, resulting in Smax reduction from ∼1200 to 800 cm/s. Considering the rather low SRV of InP [2], this value remains large and may be further reduced.
Fig. 2. Effect of chemical etching on InP TSL nanowires. Structural comparison before (a) and after (b) HF etching for 50 s. The red arrows in a and b point out the surface status before and after wet etching. (c) PL emission, (d) carrier lifetime and (e) IQE comparison of the InP TSL nanowires, before and after chemical etching. τ1 and τ2 in (d) represent the extracted lifetime for fast and slow carrier decay processes, respectively.
More quantitatively, internal quantum efficiency (IQE) can be extracted from the power dependent PL experiments (see Fig. 2(e)) using a method we have described before [30]. Briefly, the relationship between the measured PL intensity and the excitation power can be written as:
Where I is the integrated photon intensity. nrad and n0 indicate the density of carriers during radiative recombination and initial carrier density generated by optical pumping, respectively. n0 is directly proportional to the excitation power. Using Eq. (1), the PL intensity (I(P)) can be fitted as a function of excitation power to extract nrad. Then IQE is calculated by $IQE = {n_{rad}}/{n_0}$. The obtained data in Fig. 2(e) demonstrates the enhanced quantum yield in TSL after chemical etching.
Since chemical etching only changes the surface properties of InP nanowires [31] without modifying the density of both twin planes and point defects inside these nanowires, the improvement of optical performance demonstrates that surface states are the dominating non-radiative trapping centers. Chemical etching or in-situ passivation of the InP surface could further enhance its emission efficiency, as demonstrated in InGaAs/InP core/shell nanowires [32]. These results suggest that the point defect density due to lateral epilayer growth is quite low and the as-grown InP nanowires under the present growth conditions have a high crystal purity.
The recombination mechanism in InP TSL nanowires is further studied by transient PL spectroscopy, as shown in Fig. 3. During the first 10 ns after excitation, only bandgap emission is observed and no peak energy shift could be distinguished. Moreover, the early (<1.6 ns) and late (>1.6 ns) emission spectra comparison in Fig. 3(c) shows no differences. These results rule out multiple paths of emission. The periodical twin planes do not cause any mini-bands that could be detected by PL spectroscopy at room temperature [28]. Instead, these TSL nanowires only present pure ZB emission behavior.
Fig. 3. Single nanowire transient spectrum of InP TSL nanowires. (a) 2D time-energy emission map. At each time, the emission is fitted using a Gaussian, with the extracted center position shown in (b). (c) The integrated early (before 1.6 ns) and late (after 1.6 ns) spectra are shown.
Recombination due to deep centers in nanowires can be studied by temperature-dependent PL and TRPL [33]. Here, the obtained PL spectra and extracted carrier lifetime on a single nanowire with a fixed excitation power are shown in Fig. 4. The emission intensity gradually increases upon cooling as a result of improved quantum efficiency. The emission peak becomes narrower and undergoes a blue shift between the temperatures of 275 K and 100 K. Using the Varshni equation [34], the peak energy is fitted as indicated by the black curve in Fig. 4(d). The fitting becomes poor at temperatures below 50 K due to the dominance of donor-bound exciton emission. The PL spectrum taken at 10 K (Fig. 4(b)) shows a main peak at 1.411 eV, which is about 7 meV lower than the free exciton emission and is ascribed to donor-bound exciton emission due to an unintentional donor incorporation [35]. The FWHM (4.6 meV) is slightly narrower than un-etched InP TSL nanowire (6 meV) measured at a low excitation power and 4 K [19]. No lower energy peak (below 1.4 eV) is observed which has previously been attributed to acceptor-related emission or ZB/WZ heterostructure [36,37]. The absence of impurity related peak indicates that both core and the unintentional formed shell of the grown InP TSL nanowires contain a low density of defects that could be detected by PL technique. Consequently, removing the shell by wet etching to distinguish the optical performance between the InP core and the shell is not applied here. In addition to the bound-exciton emission, free exciton emission forms a small shoulder with an energy of 1.419 eV [35].
Fig. 4. Temperature dependent PL and TRPL of a single InP TSL nanowire. (a) Normalized PL spectra taken in the temperature range of 10-300 K. (b) PL spectrum at 10 K showing the strong donor bounded exciton emission with a small emission shoulder of free exciton. (c) Temperature dependent TRPL and (d) extracted carrier lifetime, bandgap and FWHM as a function of temperature.
The temperature dependent PL and TRPL can be roughly divided into three regimes:
- (1) From 10 up to ∼75 K, excitons are stable and free carriers rapidly form excitons. An unknown intrinsic point defects during InP nanowire growth play a primary role and the emission is dominated mainly by donor bound exciton emission with its energy nearly unchanged at around 1.411 eV. The near-band emission intensity becomes stronger and finally dominates over bound-exciton emission at ∼70 K. The PL intensity decay can be fitted with mono-exponential function. By comparing the integrated PL intensity at different temperatures, together with the PL lifetime, both τnr and τr can be extracted [38]. However, the absolute value for measured PL intensity for the nanowire at different temperatures could not be quantitatively determined due to the unavoidable system drift. The temperature-dependent TRPL can however be used to provide an insight into the recombination mechanism in our InP TSL nanowires. At 10 K, the extracted bound-exciton lifetime is 1.4 ns which is similar to those measured in bulk ZB InP [39], etched ZB InP nanowires [19] and is much longer than the ZB InP nanowires grown at lower temperature (400 °C) using a similar method [40]. By increasing the temperature to 80 K, the measured carrier lifetime monotonically increases to 3.6 ns. This observation is similar to those in high-quality GaAs, GaN and InP semiconductors [41–43], where τr increases and τnr decreases with temperature. We therefore believe that the carrier recombination in this range is governed by radiative bound-exciton recombination, in agreement with previous report on InP TSL nanowires [19]. Consequently, a shorter lifetime implies a higher quantum efficiency, which matches well with the qualitative enhanced emission intensity at lower temperatures.
- (2) From ∼75 to ∼155 K the carrier decay rate is relatively constant. The FWHM of the PL spectrum only slightly changes with temperature. In this region, excitons are thermally dissociated, and surface states become increasingly important. These two factors compete with each other, leading to a slow change of carrier lifetime.
- (3) Above 155 K, the carrier decay shape becomes bi-exponential with a shorter lifetime. In addition, the FWHM increases. We suggest that in this regime, all excitons are separated into free carriers due to thermal energy. Consequently, free-carrier recombination is responsible for emission. Surface states are the dominating factor in determining the carrier lifetime. Consequently, increasing the temperature leads to a drop in both carrier lifetime and emission intensity.
4. Conclusion
In conclusion, we report the carrier dynamic processes in nominal undoped InP TSL nanowires, which also have excellent optical properties. Photon emission at room temperature is limited by non-radiative recombination at the nanowire surface but with a long carrier lifetime of around 3 ns. Chemical etching is shown to boost the emission by reducing the surface states. In comparison, surface trapping effects are negligible at low temperatures and emission is dominated by donor-bound exciton. Surface-recombination is the main factor limiting the further enhancement of its optical performance at room temperature. Consequently, surface passivation is still needed for high quality InP nanowires.
Funding
National Natural Science Foundation of China (51702368, 61974166); Natural Science Foundation of Hunan Province (2018JJ3684); Australian Research Council; Open Project of the State Key Laboratory of Luminescence and Applications (SKLA-2018-07); Innovation-Driven Project of Central South University (2018CX045); Royal Society Paul Instrument Fund (PI150018); Independent Exploration and Innovation Project for Postgraduates of Central South University (2018ttzs103).
Acknowledgements
The Australian National Fabrication Facility, ACT Node and the Australian Microscopy and Microanalysis Research Facility are acknowledged for access to facilities used in this work.
Disclosures
The authors declare no conflicts of interest.
References
1. L. Güniat, P. Caroff, and A. F. i. Morral, “Vapor Phase Growth of Semiconductor Nanowires: Key Developments and Open Questions,” Chem. Rev. 119(15), 8958–8971 (2019). [CrossRef]
2. H. J. Joyce, J. Wong-Leung, C.-K. Yong, C. J. Docherty, S. Paiman, Q. Gao, H. H. Tan, C. Jagadish, J. Lloyd-Hughes, L. M. Herz, and M. B. Johnston, “Ultralow Surface Recombination Velocity in InP Nanowires Probed by Terahertz Spectroscopy,” Nano Lett. 12(10), 5325–5330 (2012). [CrossRef]
3. K. Oda, “Toxicity of a Low Level of Indium Phosphide (InP) in Rats after Intratracheal Instillation,” Ind. Health 35(1), 61–68 (1997). [CrossRef]
4. Q. Gao, D. Saxena, F. Wang, L. Fu, S. Mokkapati, Y. Guo, L. Li, J. Wong-Leung, P. Caroff, H. H. Tan, and C. Jagadish, “Selective-Area Epitaxy of Pure Wurtzite InP Nanowires: High Quantum Efficiency and Room-Temperature Lasing,” Nano Lett. 14(9), 5206–5211 (2014). [CrossRef]
5. J. Wallentin, N. Anttu, D. Asoli, M. Huffman, I. Åberg, M. H. Magnusson, G. Siefer, P. Fuss-Kailuweit, F. Dimroth, B. Witzigmann, H. Q. Xu, L. Samuelson, K. Deppert, and M. T. Borgström, “InP Nanowire Array Solar Cells Achieving 13.8% Efficiency by Exceeding the Ray Optics Limit,” Science 339(6123), 1057–1060 (2013). [CrossRef]
6. M. Yoshimura, E. Nakai, K. Tomioka, and T. Fukui, “Indium Phosphide Core–Shell Nanowire Array Solar Cells with Lattice-Mismatched Window Layer,” Appl. Phys. Express 6(5), 052301 (2013). [CrossRef]
7. N. Kornienko, N. A. Gibson, H. Zhang, S. W. Eaton, Y. Yu, S. Aloni, S. R. Leone, and P. Yang, “Growth and Photoelectrochemical Energy Conversion of Wurtzite Indium Phosphide Nanowire Arrays,” ACS Nano 10(5), 5525–5535 (2016). [CrossRef]
8. S. J. Gibson, B. van Kasteren, B. Tekcan, Y. Cui, D. van Dam, J. E. M. Haverkort, E. P. A. M. Bakkers, and M. E. Reimer, “Tapered InP nanowire arrays for efficient broadband high-speed single-photon detection,” Nat. Nanotechnol. 14(5), 473–479 (2019). [CrossRef]
9. K. Peng, P. Parkinson, J. L. Boland, Q. Gao, Y. C. Wenas, C. L. Davies, Z. Li, L. Fu, M. B. Johnston, H. H. Tan, and C. Jagadish, “Broadband Phase-Sensitive Single InP Nanowire Photoconductive Terahertz Detectors,” Nano Lett. 16(8), 4925–4931 (2016). [CrossRef]
10. D. Zheng, J. Wang, W. Hu, L. Liao, H. Fang, N. Guo, P. Wang, F. Gong, X. Wang, Z. Fan, X. Wu, X. Meng, X. Chen, and W. Lu, “When Nanowires Meet Ultrahigh Ferroelectric Field-High-Performance Full-Depleted Nanowire Photodetectors,” Nano Lett. 16(4), 2548–2555 (2016). [CrossRef]
11. G. Zhang, M. Takiguchi, K. Tateno, T. Tawara, M. Notomi, and H. Gotoh, “Telecom-band lasing in single InP/InAs heterostructure nanowires at room temperature,” Sci. Adv. 5(2), eaat8896 (2019). [CrossRef]
12. V. Gautam, S. Naureen, N. Shahid, Q. Gao, Y. Wang, D. Nisbet, C. Jagadish, and V. R. Daria, “Engineering Highly Interconnected Neuronal Networks on Nanowire Scaffolds,” Nano Lett. 17(6), 3369–3375 (2017). [CrossRef]
13. M. E. Reimer, G. Bulgarini, N. Akopian, M. Hocevar, M. B. Bavinck, M. A. Verheijen, E. Bakkers, L. P. Kouwenhoven, and V. Zwiller, “Bright single-photon sources in bottom-up tailored nanowires,” Nat. Commun. 3(1), 737 (2012). [CrossRef]
14. M. A. M. Versteegh, M. E. Reimer, K. D. Jöns, D. Dalacu, P. J. Poole, A. Gulinatti, A. Giudice, and V. Zwiller, “Observation of strongly entangled photon pairs from a nanowire quantum dot,” Nat. Commun. 5(1), 5298 (2014). [CrossRef]
15. P. Mohan, J. Motohisa, and T. Fukui, “Controlled growth of highly uniform, axial/radial direction-defined, individually addressable InP nanowire arrays,” Nanotechnology 16(12), 2903–2907 (2005). [CrossRef]
16. R. E. Algra, M. A. Verheijen, M. T. Borgstrom, L. F. Feiner, G. Immink, W. J. van Enckevort, E. Vlieg, and E. P. Bakkers, “Twinning superlattices in indium phosphide nanowires,” Nature 456(7220), 369–372 (2008). [CrossRef]
17. X. Yuan, Y. Guo, P. Caroff, J. He, H. H. Tan, and C. Jagadish, “Dopant-Free Twinning Superlattice Formation in InSb and InP Nanowires,” Phys. Status Solidi RRL 11(11), 1700310 (2017). [CrossRef]
18. Q. Xiong, J. Wang, and P. C. Eklund, “Coherent Twinning Phenomena: Towards Twinning Superlattices in III−V Semiconducting Nanowires,,” Nano Lett. 6(12), 2736–2742 (2006). [CrossRef]
19. T. T. Vu, T. Zehender, M. A. Verheijen, S. R. Plissard, G. W. Immink, J. E. Haverkort, and E. P. Bakkers, “High optical quality single crystal phase wurtzite and zincblende InP nanowires,” Nanotechnology 24(11), 115705 (2013). [CrossRef]
20. R. L. Woo, R. Xiao, Y. Kobayashi, L. Gao, N. Goel, M. K. Hudait, T. E. Mallouk, and R. F. Hicks, “Effect of Twinning on the Photoluminescence and Photoelectrochemical Properties of Indium Phosphide Nanowires Grown on Silicon (111),” Nano Lett. 8(12), 4664–4669 (2008). [CrossRef]
21. Z. Liu, I. Papadimitriou, M. Castillo-Rodrígueza, C. Wang, G. Esteban-Manzanares, X. Yuan, H. H. Tan, J. M. Molina-Aldareguía, and J. Llorca, “Mechanical behavior of InP twinning superlattice nanowires,” Nano Lett. 19(7), 4490–4497 (2019). [CrossRef]
22. L. E. Black, A. Cavalli, M. A. Verheijen, J. E. M. Haverkort, E. P. A. M. Bakkers, and W. M. M. Kessels, “Effective Surface Passivation of InP Nanowires by Atomic-Layer-Deposited Al2O3 with POx Interlayer,” Nano Lett. 17(10), 6287–6294 (2017). [CrossRef]
23. W. Zhang, S. Lehmann, K. Mergenthaler, J. Wallentin, M. T. Borgstrom, M. E. Pistol, and A. Yartsev, “Carrier Recombination Dynamics in Sulfur-Doped InP Nanowires,” Nano Lett. 15(11), 7238–7244 (2015). [CrossRef]
24. T. L. Atallah, A. V. Sica, A. J. Shin, H. C. Friedman, Y. K. Kahrobai, and J. R. Caram, “Decay-Associated Fourier Spectroscopy: Visible to Shortwave Infrared Time-Resolved Photoluminescence Spectra,” J. Phys. Chem. A 123(31), 6792–6798 (2019). [CrossRef]
25. J. V. Knutsson, S. Lehmann, M. Hjort, P. Reinke, E. Lundgren, K. A. Dick, R. Timm, and A. Mikkelsen, “Atomic Scale Surface Structure and Morphology of InAs Nanowire Crystal Superlattices: The Effect of Epitaxial Overgrowth,” ACS Appl. Mater. Interfaces 7(10), 5748–5755 (2015). [CrossRef]
26. C. Himwas, S. Collin, P. Rale, N. Chauvin, G. Patriarche, F. Oehler, F. H. Julien, L. Travers, J. C. Harmand, and M. Tchernycheva, “In situ passivation of GaAsP nanowires,” Nanotechnology 28(49), 495707 (2017). [CrossRef]
27. X. Su, X. Zeng, H. Nemec, X. Zou, W. Zhang, M. T. Borgstrom, and A. Yartsev, “Effect of hydrogen chloride etching on carrier recombination processes of indium phosphide nanowires,” Nanoscale 11(40), 18550–18558 (2019). [CrossRef]
28. C. K. Yong, J. Wong-Leung, H. J. Joyce, J. Lloyd-Hughes, Q. Gao, H. H. Tan, C. Jagadish, M. B. Johnston, and L. M. Herz, “Direct observation of charge-carrier heating at WZ-ZB InP nanowire heterojunctions,” Nano Lett. 13(9), 4280–4287 (2013). [CrossRef]
29. S. Breuer, C. Pfuller, T. Flissikowski, O. Brandt, H. T. Grahn, L. Geelhaar, and H. Riechert, “Suitability of Au- and self-assisted GaAs nanowires for optoelectronic applications,” Nano Lett. 11(3), 1276–1279 (2011). [CrossRef]
30. X. Yuan, L. Li, Z. Li, F. Wang, N. Wang, L. Fu, J. He, H. H. Tan, and C. Jagadish, “Unexpected benefits of stacking faults on the electronic structure and optical emission in wurtzite GaAs/GaInP core/shell nanowires,” Nanoscale 11(18), 9207–9215 (2019). [CrossRef]
31. M. Hjort, J. Wallentin, R. Timm, A. A. Zakharov, U. Håkanson, J. N. Andersen, E. Lundgren, L. Samuelson, M. T. Borgström, and A. Mikkelsen, “Surface Chemistry, Structure, and Electronic Properties from Microns to the Atomic Scale of Axially Doped Semiconductor Nanowires,” ACS Nano 6(11), 9679–9689 (2012). [CrossRef]
32. A. Higuera-Rodriguez, B. Romeira, S. Birindelli, L. E. Black, E. Smalbrugge, P. J. van Veldhoven, W. M. Kessels, M. K. Smit, and A. Fiore, “Ultralow Surface Recombination Velocity in Passivated InGaAs/InP Nanopillars,” Nano Lett. 17(4), 2627–2633 (2017). [CrossRef]
33. P. Corfdir, C. Hauswald, J. K. Zettler, T. Flissikowski, J. Lähnemann, S. Fernández-Garrido, L. Geelhaar, H. T. Grahn, and O. Brandt, “Stacking faults as quantum wells in nanowires: Density of states, oscillator strength, and radiative efficiency,” Phys. Rev. B 90(19), 195309 (2014). [CrossRef]
34. Y. P. Varshni, “Temperature dependence of the energy gap in semiconductors,” Physica 34(1), 149–154 (1967). [CrossRef]
35. P. J. Dean and M. S. Skolnick, “Donor discrimination and bound exciton spectra in InP,” J. Appl. Phys. 54(1), 346–359 (1983). [CrossRef]
36. J. Bao, D. C. Bell, F. Capasso, J. B. Wagner, T. Mårtensson, J. Trägårdh, and L. Samuelson, “Optical Properties of Rotationally Twinned InP Nanowire Heterostructures,” Nano Lett. 8(3), 836–841 (2008). [CrossRef]
37. N. Akopian, G. Patriarche, L. Liu, J. C. Harmand, and V. Zwiller, “Crystal phase quantum dots,” Nano Lett. 10(4), 1198–1201 (2010). [CrossRef]
38. T. Onuma, K. Hazu, A. Uedono, T. Sota, and S. F. Chichibu, “Identification of extremely radiative nature of AlN by time-resolved photoluminescence,” Appl. Phys. Lett. 96(6), 061906 (2010). [CrossRef]
39. U. Heim, “Lifetimes of bound excitons in InP,” Phys. Status Solidi B 48(2), 629–633 (1971). [CrossRef]
40. S. Paiman, Q. Gao, H. H. Tan, C. Jagadish, K. Pemasiri, M. Montazeri, H. E. Jackson, L. M. Smith, J. M. Yarrison-Rice, X. Zhang, and J. Zou, “The effect of V/III ratio and catalyst particle size on the crystal structure and optical properties of InP nanowires,” Nanotechnology 20(22), 225606 (2009). [CrossRef]
41. H. Kim, A. Murayama, J. Kim, and J. Song, “Temperature dependence of the radiative recombination time in laterally coupled GaAs quantum dots,” Appl. Surf. Sci. 457, 497–500 (2018). [CrossRef]
42. W. Yang, J. Li, Y. Zhang, P.-K. Huang, T.-C. Lu, H.-C. Kuo, S. Li, X. Yang, H. Chen, D. Liu, and J. Kang, “High density GaN/AlN quantum dots for deep UV LED with high quantum efficiency and temperature stability,” Sci. Rep. 4(1), 5166 (2015). [CrossRef]
43. R. Roßbach, W. M. Schulz, M. Reischle, G. J. Beirne, M. Jetter, and P. Michler, “Red to green photoluminescence of InP-quantum dots in AlxGa1-xInP,” J. Cryst. Growth 298, 595–598 (2007). [CrossRef]
