Open Access
Add to BibSonomyAbstract
An innovative solar cell based on inclined p-i-n nanowire array is designed and analyzed. The results show that the inclined geometry can sufficiently increase the conversion efficiency of solar cells by enhancing the absorption of light in the active region. By tuning the nanowire array density, nanowire diameter, nanowire length, as well as the proportion of intrinsic region of the inclined nanowire solar cell, a remarkable efficiency in excess of 16% can be obtained in GaAs. Similar results have been obtained in InP and Si nanowire solar cells, demonstrating the universality of the performance enhancement of inclined nanowire arrays.
© 2015 Optical Society of America
1. Introduction
Semiconductor nanowire arrays (NWAs) have attracted great attention in the field of photovoltaics due to their unique optical properties, such as anti-reflection and light-trapping [1,2,12,13 ]. In addition, the quasi-one-dimensional geometry of NW can lead to a reduction of materials usage and high tolerance of lattice-mismatch, enabling the realization of low-cost and high-performance solar cells [3,4,10,11,19 ]. For a NWA solar cell, the key part is the p(i)n junction, which absorbs the light and converts the photons into electron-hole pairs. Axial NW p-i-n junctions have been widely used in the NWA solar cell due to their high open-circuit voltage and technically feasibility for multi-junction NW solar cells [6,7 ]. For example, efficiencies of 13.8% and 7.58% have been obtained in InP and GaAs axial NW p-i-n array solar cells, respectively [5,8 ]. However, the axial p-i-n NWA solar cell has an intrinsic disadvantage. A great number of photocarriers are generated near the top of the NW, which typically belongs to the zero-electric-field and highly doped p(n) region. These photocarriers are quickly recombined and cannot contribute to the photocurrent, which strongly limit the conversion efficiency.
So far, much attention has been focused on the optimization of the parameters of NWA, e. g. D/P ratio, diameter, length, etc, for a better absorption of light [9,14,15,20,21 ]. However, as only the light absorbed by the intrinsic region of the p-i-n NW contributes to the photocurrent, an enhancement of light absorption in the intrinsic(active) region is critical for the improvement of conversion efficiency. In the case of a typical vertical axial p-i-n NWA, the incident light should pass through the p(n) region before absorbed by the active region, leading to a great loss of light. If the NWA is tilted from the substrate, much of the incident light can be directly absorbed by the active region without passing through the p(n) region, which is expected to greatly enhance the absorption of the active region and raise the efficiency. Tilted NWA can be obtained by growing typical <111> NWs on non-<111> substrate, e. g. <100> or <110>, or growing novel non-<111>-oriented NWs. For example, <111>, <112>, and <110>-oriented ZnSe NWs have been obtained on the GaAs (111) substrate [16]. <110> and <112>-oriented GaAs NWs have also been reported [17,18 ]. However, to our knowledge, there have been no theoretical or experimental reports on tilted NWA solar cells.
In this paper, a coupled three-dimensional (3-D) optoelectronic simulation is presented to investigate the photovoltaic performance of an inclined GaAs NWA solar cell. First, a comparison in light absorptance between the vertical and inclined NWAs is made by using finite-difference time-domain (FDTD) simulations. Second, the photo-generation profiles are incorporated into the electrical simulations to perform the calculation of the current density versus voltage (J-V) characteristics using finite element method (FEM), and a distinct enhancement in conversion efficiency is achieved in inclined NWA solar cells versus the vertical counterpart. Third, by tuning the nanowire array density, nanowire diameter, nanowire length, as well as the proportion of intrinsic region of the inclined nanowire solar cell, a remarkable efficiency in excess of 16% can be obtained in GaAs. In addition, the performance of NWA solar cells based on other two materials commonly used in solar cells, InP and Si, is also investigated, demonstrating the universality of the performance enhancement of inclined NWAs.
2. Device geometry and simulation methodology
Figure 1(a) illustrates a schematic drawing of the inclined NWA solar cell. The NWA consists of periodic GaAs axial p-i-n NWs with diameter D = 200 nm, period P = 400 nm and length L = 800 nm, as shown in Fig. 1(b). Both the n- and p-regions have a length of 160 nm and are uniformly doped to 1 × 1017 and 3 × 1018 cm−3, respectively. The GaAs substrate is n-doped with the carrier concentration fixed at 1 × 1017 cm−3. In the simulation, two cases in which NWs grow in <110> and <112> directions on <111> substrates are selected and the corresponding oblique angles are 35.3° and 19.5° respectively. A typical vertical <111> NWA solar cell is also investigated for comparison. The D/P ratio determined by the period of the square lattice (P) and the diameter of NWs (D) is set to 0.5 and the array is illuminated by sunlight from the top. The inset in Fig. 1(b) illustrates the illumination geometry for the transverse-electric (electric field of the light polarized perpendicular to the inclined direction of the wire) and transverse-magnetic (electric field of the light polarized parallel to the inclined direction of the wire) polarizations.
Fig. 1 (a) 3-D illustration of the inclined NWA solar cell. (b) Schematic drawings of GaAs NWs with orientation of <110> and <112> grow on <111> substrates. The inset illustrates the illumination geometry for the TE and TM polarizations.
Optical properties of the structures are investigated through Sentaurus Electromagnetic Wave (EMW) Solver module package. The inclined NWA and its vertical counterpart are theoretically analyzed by using 3-D FDTD simulations [22–24 ].The minimum cell size of the FDTD mesh is set to 5 nm, and the number of nodes per wavelength is 20 in all directions. By placing periodic boundary conditions, the simulations can be carried out in a single unit cell to model the periodic array structure. In order to save the resources and time required for the calculation, the thickness of the GaAs substrate is limited to 0.4 μm. However, by using a perfect match layer (PML) adjacent to the GaAs substrate, the transmission light is totally absorbed, which enables us to model a semi-infinite GaAs substrate [25]. The wavelength-dependent complex refractive index used in the simulations is obtained from Levinshtein’s work [28]. Normally, incident light is defined with power intensity and wavelength values from a discretized AM 1.5G solar spectrum. The AM 1.5G spectrum is divided into 62 discrete wavelength intervals, from 290 to 900 nm. The transverse electric (TE) and transverse magnetic (TM) mode contributions are superimposed to model the corresponding unpolarized feature of sunlight [29]. The total optical generation under AM 1.5G illumination can be modeled by superimposing the power-weighted single wavelength optical generation rates [21]. The optical generation rate Gph is obtained from the Poynting vector S:
whereis the reduced Planck's constant, ω is the angular frequency of the incident light, E is the electric field intensity at each grid point, and ε” is the imaginary part of the permittivity.For the electrical modeling, the 3-D optical generation profiles are incorporated into the finite-element mesh of the NWs in the electrical tool [30], which solves the carrier continuity equations coupled with Poisson’s equation self-consistently in 3D. The doping-dependent mobility, bandgap narrowing, and radiative, Auger and Shockley-Reed-Hall (SRH) recombination are taken into consideration in the device electrical simulation. The critical material parameters for device simulations are mostly obtained from the Levinshtein’s model [28].
3. Results and discussion
The 3-D total optical generation profiles under AM 1.5G illumination in half of the structure are shown in Fig. 2 . We can see that the majority of light absorption concentrates at the top and sidewall of the NWs in the vertical case. By contrast, in the inclined NWAs, more photogeneration events take place in the i-region as the incident light can be directly absorbed by the active i-region, and the phenomenon becomes more remarkable for larger tilt angle, as illustrated in Figs. 2(b) and 2(c), corresponding to the growth direction of <112> and <110> on <111> substrate, respectively. The recombination of photon-generated carriers is expected to be high in the top p-segment due to the high doping concentration [31–33 ] and an absence of electric-field for separating electron-holes, leading to a substantial loss of incident light. Therefore, performance enhancement can be achieved in the inclined NWAs due to a more efficient light absorption in i-region compared with their vertical counterpart. The diameter and D/P ratio of the NWAs are set to 200 nm and 0.5 in all the considered structures.
Fig. 2 The 3-D total optical generation profiles under AM 1.5G illumination in half of the structure, which correspond to the vertical NWAs (a) and inclined NWAs with growth direction along <112> (b) and <110> (c) on <111> substrates, respectively.
To further investigate the optical generation enhancement in inclined NWAs, absorption spectra are calculated, as presented in Fig. 3 . In the case of the inclined NWAs, the device structure is no longer isotropic in the x-y plane, leading to a divergence between the absorptance of TE and TM polarized light, while the vertical NWA is not sensitive to polarization. In an inclined NWA, TM polarization has higher absorption than TE polarization due to an enhanced optical antenna effect for each NW in TM polarization [34], and this is extremely evident in the absorption of i-region. Compared with the vertical NWA, inclined NWA shows an increase in light absorption which mainly comes from TM component of the light, or more accurately, the TM component of the light absorbed in i-region, as the absorption in i-region takes up large proportions of the overall absorption, which can be figured out in Fig. 3(b). As the principal enhancement in absorption happens in i-region, the increased photo-generated carriers can contribute to the conversion efficiency effectively. However, the absorption in the i-region at short wavelength region (λ<400 nm) of inclined NWA shows no advantage over that of the vertical counterpart, as the photo generations are concentrated near the top of the NWs and the reflection is more obvious in inclined NWA under TE polarization at that wavelength region. Furthermore, the enhancement effect in i-region of the NWs in <110> direction is higher than that of the NWs along <112> direction, which further validates the conclusion obtained from Fig. 2. The lower part of Fig. 3 shows the vertical cross sections of optical generation profiles at wavelength of 600 nm and 800 nm under TM polarization in NWAs, demonstrating the promoting effect of inclined NWs on light absorption.
Fig. 3 The absorption spectra of whole NW (solid lines) and i-region (dash lines) under TE polarization (a) and TM polarization (b) of the simulated GaAs inclined NWA in the case of <112> and <110> on <111> substrates compared with their vertical counterparts. (c) vertical cross sections of optical generation profiles at wavelength of 600 nm and 800 nm. The diameter and D/P ratio of the NWA are fixed at 200 nm and 0.5.
Further studies focus on the investigation of the potential increase in photovoltaic efficiency gains stemming from the absorption enhancement effect in inclined NWA. Previously simulated 3D photogeneration profiles are incorporated into the electrical tool [30] to calculate the terminal current-voltage characteristics of NWA solar cells. The J-V characteristics in Fig. 4 show that the effective light absorption enhancement in inclined NWA leads to an increase of the short-circuit current (Jsc). The inclined NWA with growth direction along <110> yields a Jsc of 19.4 mA/cm2 (3 mA/cm2 higher than the vertical one) and an open-circuit voltage (Voc) of 0.905 V (slight higher than the vertical NWA), resulting in a higher conversion efficiency (η) of 14.2% compared with 11.7% of vertical NWA. While the NWA grow in <112> direction yields a short-circuit current (Jsc) of 18.3 mA/cm2 and an open-circuit voltage (Voc) of 0.895 V, achieving conversion efficiency of 13.2%. The results imply that inclined NWA solar cell with a larger tilt angle has a better performance.
Fig. 4 The simulated J-V characteristics of the vertical NWA and inclined NWA with growth direction of <110> and <112> on <111> substrates. The Jsc and conversion efficiency are normalized to the substrate area and the detailed performance parameters are summarized in the figure.
As the light absorption of the NWAs is quite sensitive to structural parameters [9,14,15,20,21 ], it is necessary to investigate the photovoltaic characteristics of inclined NWAs under different D/P ratios and NW diameters for optimizing the device performance. To assess the effects of the D/P ratio on the performance of NWA solar cells, the absorptance and photovoltaic efficiency of both inclined and vertical NWAs are calculated under different D/P ratios, with the diameter of 200 nm. Since the photo-generated carriers in i-region account for most of the efficiency, the absorptance in i-region under various D/P ratios is plotted instead of the whole NWA, as shown in Fig. 5(a) . The results show that the absorption curve trends of inclined and vertical NWAs are quite similar: the absorptance increases with the D/P ratio when NWs are sparsely arranged and drops when the D/P ratio exceeds 0.5. It can be noticed that for all the considered D/P ratios, inclined NWAs have higher absorptance in i-region than the vertical ones and the maximum enhancement of 8% occurs at D/P ratio of 0.5. The efficiency curves coincide well with i-region absorptance curves, as the higher absorptance leads to higher Jsc. The highest efficiency of 14.2% occurs at D/P ratio of 0.5 in the case of <110> NWA grow on <111> substrate, 2.5% higher than the efficiency of vertical-aligned NWA with the same D/P ratio.
Fig. 5 The absorption of i-region under different D/P ratios (a) and radius (b). The conversion efficiency under different D/P ratios (c) and radius (d).
To find out an optimized geometry, the absorptance and conversion efficiency of i-region under different diameters at a fixed D/P ratio of 0.5 (at which the highest efficiency is obtained among various D/P ratios) are calculated. In order to make a fair comparison, the diameters are measured perpendicular to the NWs axis. The highest absorption in all of the calculated NWAs occurs around radius of 85 nm and the dependence of absorption on diameter in inclined NWs is similar with that in vertical NWs, which can be explained by guided-resonance modes in NWs [15,25–27 ]. In the case of NWs with smaller diameter, fewer modes can be coupled into the NW, which leads to insufficient absorption. By contrast, NWs with larger diameters can support more modes, leading to an increased absorption. However, as the diameter of NWs further increases, both the reflection at the top surface of NWA and the transmission at long wavelength region increase. The enhanced absorption in i-region in inclined NWAs is obvious under all of the diameters and so is the efficiency, with the maximum enhancement in absorption of 5% and efficiency of 1.3%.
As the optical generation in i-region determines the final efficiency, the length of i-region is expected to have a great influence on the performance of NWAs. With the increase of the length of i-region, the conversion efficiency monotonically increases in all the device structures considered, as illustrated in Fig. 6 . For a fixed NW length of 800 nm, as the proportion of i-region increases from 35% to 85%, the efficiency of vertical and inclined NWs grown along <110> and <112> increases by 5.15%, 5.1% and 4.6%, respectively. The results agree well with Wallentin et al.’s report, in which the reduction of the nominal n-segment length leads to less recombination loss, and an enhanced average Jsc [5]. However, longer i-region means shorter top n-/p-region, leading to more difficulties for making contacts.
Fig. 6 The conversion efficiency with different proportions of i region (a) and lengths of NW (b). The diameter and D/P ratio of the NWA are fixed at 200 nm and 0.5.
The influence of NW lengths on conversion efficiency has also been discussed. We calculate the efficiency with different NW lengths ranging from 800 nm to 2500 nm. The length of p(n) region is fixed at 160 nm, at which the difficulty for making contacts in experiments can be reduced. The efficiencies increase significantly with the length of the NW in both inclined and vertical NWAs due to more sufficient light absorption in longer NWs, and the efficiency increases more quickly in NWAs with smaller tilt angles.
The simulation model mentioned above does not include surface recombination, however, with the large surface/volume ratio, the electronic properties of NW based devices are heavily affected by surface recombination, especially for GaAs, which has a high surface recombination velocity (SRV) of 106-107 cm/s. It has been reported that the SRV of GaAs nanowires can be reduced to 103 cm/s by growing a AlGaAs capping shell or soaking the sample in ammonium polysulfide solution (NH4)2Sx for passivation [35–37 ]. To access the damage induced by surface recombination, we calculate the performance of solar cells with various SRVs. As illustrated in Fig. 7 , both Jsc and Voc decrease significantly with a SRV higher than 104 cm/s for all of the NWAs. The results conform with that reported by Wang et al. [38]. In resisting the damage induced by surface recombination, the inclined NWAs show no advantage over their vertical counterparts, the efficiency decreases by 7.99% in vertical NWAs, 8.96% in inclined NWA grown along <112> direction and 9.5% in NWA grown along <110> direction. As in axial pin junctions, with the i-region exposes to the surface, the inclined NWAs are more vulnerable to surface recombination due to their higher absorption in i-region. However, the efficiency in inclined NWAs is still higher than that of the vertical NWAs, even with a high SRV of 107 cm/s. And from the calculated results we can conclude that surface passivation is important for achieving high-performance GaAs nanowire solar cells.
Fig. 7 The Jsc (a), Voc (b) and conversion efficiency (c) of the solar cells with various SRVs for both inclined and vertical NWAs. The diameter and D/P ratio of the NWAs are fixed at 200 nm and 0.5.
To demonstrate the universality of the photovoltaic enhancement of the inclined NWAs, devices based on other semiconductor materials are also investigated. We choose InP, suitable for the solar spectrum with a direct band gap of 1.34 eV, and Si, the most commonly used material in solar cells at present for study. The results show an excellent agreement with the calculation result of the GaAs NWs, as shown in Fig. 8 , indicating a universal applicability of the structure. It can be concluded that the increase of Jsc is the key factor for the efficiency enhancement in inclined NWA solar cells compared with their vertical counterparts, which can be explained by the improved absorption in i-region.
Fig. 8 The simulated J-V characteristics of the vertical NWA and inclined NWA with growth direction of <110> and <112> on <111>, composed of InP (a) and Silicon (b), the detailed performance parameters are summarized in the figure. The diameter and D/P ratio of the NWA are fixed at 200 nm and 0.5.
4. Conclusion
In summary, we have studied the photovoltaic performance of the inclined p-i-n GaAs NWA based solar cells. Compared with the vertical NWA, the inclined NWA can absorb sunlight more efficiently in active i-region and achieve higher conversion efficiency. To optimize the device performance, the efficiency under different D/P ratios, NW diameters, NW lengths and proportion of intrinsic region are calculated. The other two kinds of generally studied materials of solar cells, InP and Si, are also taken into account in this article, demonstrating the universality of the photovoltaic enhancement of the inclined NWAs. Judging from the calculation result in this paper, we can conclude that inclined NWAs are expected to be a promising solution for optimizing the axial pin junction NWA solar cells.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (NSFC) (61376019, 61504010 and 61511130045), the Natural Science Foundation of Beijing (4142038), the Specialized Research Fund for the Doctoral Program of Higher Education (20120005110011), the Fundamental Research Funds for the Central Universities (2015RC13), and the Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), P. R. China.
References and links
1. X. Cao, P. Chen, and Y. Guo, “Decoration of textured ZnO nanowires array with CdTe quantum dots: enhanced light-trapping effect and photogenerated charge separation,” J. Phys. Chem. C 112(51), 20560–20566 (2008). [CrossRef]
2. E. Garnett and P. Yang, “Light trapping in silicon nanowire solar cells,” Nano Lett. 10(3), 1082–1087 (2010). [CrossRef] [PubMed]
3. J. A. Czaban, D. A. Thompson, and R. R. LaPierre, “GaAs core--shell nanowires for photovoltaic applications,” Nano Lett. 9(1), 148–154 (2009). [CrossRef] [PubMed]
4. E. C. Garnett and P. Yang, “Silicon nanowire radial p-n junction solar cells,” J. Am. Chem. Soc. 130(29), 9224–9225 (2008). [CrossRef] [PubMed]
5. J. Wallentin, N. Anttu, D. Asoli, M. Huffman, I. Aberg, 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] [PubMed]
6. M. Heurlin, P. Wickert, S. Fält, M. T. Borgström, K. Deppert, L. Samuelson, and M. H. Magnusson, “Axial InP nanowire tandem junction grown on a silicon substrate,” Nano Lett. 11(5), 2028–2031 (2011). [CrossRef] [PubMed]
7. N. Huang, C. Lin, and M. L. Povinelli, “Limiting efficiencies of tandem solar cells consisting of III-V nanowire arrays on silicon,” J. Appl. Phys. 112(6), 064321 (2012). [CrossRef]
8. M. Yao, N. Huang, S. Cong, C. Y. Chi, M. A. Seyedi, Y. T. Lin, Y. Cao, M. L. Povinelli, P. D. Dapkus, and C. Zhou, “GaAs nanowire array solar cells with axial p-i-n junctions,” Nano Lett. 14(6), 3293–3303 (2014). [CrossRef] [PubMed]
9. J. Kupec, R. L. Stoop, and B. Witzigmann, “Light absorption and emission in nanowire array solar cells,” Opt. Express 18(26), 27589–27605 (2010). [CrossRef] [PubMed]
10. L. Tsakalakos, J. Balch, J. Fronheiser, B. A. Korevaar, O. Sulima, and J. Rand, “Silicon nanowire solar cells,” Appl. Phys. Lett . 91(23), 233117 (2007). [CrossRef] [PubMed]
11. R. Yan, D. Gargas, and P. Yang, “Nanowire photonics,” Nat. Photonics 3(10), 569–576 (2009). [CrossRef]
12. J. Zhu, Z. Yu, G. F. Burkhard, C. M. Hsu, S. T. Connor, Y. Xu, Q. Wang, M. McGehee, S. Fan, and Y. Cui, “Optical absorption enhancement in amorphous silicon nanowire and nanocone arrays,” Nano Lett. 9(1), 279–282 (2009). [CrossRef] [PubMed]
13. A. Convertino, M. Cuscuna, S. Rubini, and F. Martelli, “Optical reflectivity of GaAs nanowire arrays: experiment and model,” J. Appl. Phys. 111(11), 114302 (2012). [CrossRef]
14. L. Hu and G. Chen, “Analysis of optical absorption in silicon nanowire arrays for photovoltaic applications,” Nano Lett. 7(11), 3249–3252 (2007). [CrossRef] [PubMed]
15. Z. Gu, P. Prete, N. Lovergine, and B. Nabet, “On optical properties of GaAs and GaAs/AlGaAs core-shell periodic nanowire arrays,” J. Appl. Phys. 109(6), 064314 (2011). [CrossRef]
16. Y. Cai, S. K. Chan, I. K. Sou, Y. F. Chan, D. S. Su, and N. Wang, “The size-dependent growth direction of ZnSe nanowires,” Adv. Mater. 18(1), 109–114 (2006). [CrossRef]
17. X. Zhang, V. G. Dubrovskii, N. V. Sibirev, G. E. Cirlin, C. Sartel, M. Tchernycheva, J. C. Harmand, and F. Glas, “Growth of inclined GaAs nanowires by molecular beam epitaxy: theory and experiment,” Nanoscale Res. Lett. 5(10), 1692–1697 (2010). [CrossRef] [PubMed]
18. Z. H. Wu, X. Mei, D. Kim, M. Blumin, H. E. Ruda, J. Q. Liu, and K. L. Kavanagh, “Growth, branching, and kinking of molecular-beam epitaxial< 110> GaAs nanowires,” Appl. Phys. Lett. 83(16), 3368–3370 (2003). [CrossRef]
19. C. Colombo, M. Heiß, M. Grätzel, and A. F. Morra, “Gallium arsenide pin radial structures for photovoltaic applications,” Appl. Phys. Lett. 94(17), 173108 (2009). [CrossRef]
20. N. Anttu, A. Abrand, D. Asoli, M. Heurlin, I. Åberg, L. Samuelson, and M. Borgström, “Absorption of light in InP nanowire arrays,” Nano Res. 7(6), 816–823 (2014). [CrossRef]
21. L. Wen, Z. Zhao, X. Li, Y. Shen, H. Guo, and Y. Wang, “Theoretical analysis and modeling of light trapping in high efficicency GaAs nanowire array solar cells,” Appl. Phys. Lett. 99(14), 143116 (2011). [CrossRef]
22. W. Q. Xie, W. F. Liu, J. I. Oh, and W. Z. Shen, “Optical absorption in c-Si/a-Si: H core/shell nanowire arrays for photovoltaic applications,” Appl. Phys. Lett. 99(3), 033107 (2011). [CrossRef]
23. M. Zanuccoli, I. Semenihin, J. Michallon, E. Sangiorgi, and C. Fiegna, “Advanced electro-optical simulation of nanowire-based solar cells,” J. Comput. Electron. 12(4), 572–584 (2013). [CrossRef]
24. N. Huang, C. Lin, and M. L. Povinelli, “Limiting efficiencies of tandem solar cells consisting of III-V nanowire arrays on silicon,” J. Appl. Phys. 112(6), 064321 (2012). [CrossRef]
25. L. Wen, X. Li, Z. Zhao, S. Bu, X. Zeng, J. H. Huang, and Y. Wang, “Theoretical consideration of III-V nanowire/Si triple-junction solar cells,” Nanotechnology 23(50), 505202 (2012). [CrossRef] [PubMed]
26. K. D. Song, T. J. Kempa, H. G. Park, and S. K. Kim, “Laterally assembled nanowires for ultrathin broadband solar absorbers,” Opt. Express 22(S3Suppl 3), A992–A1000 (2014). [CrossRef] [PubMed]
27. K. T. Fountaine, W. S. Whitney, and H. A. Atwater, “Resonant absorption in semiconductor nanowires and nanowire arrays: relating leaky waveguide modes to Bloch photonic crystal modes,” J. Appl. Phys. 116(15), 153106 (2014). [CrossRef]
28. M. Levinshtein, S. Rumyantsev, and M. Shur, Handbook Series on Semiconductor Parameters, Ternary, and Quaternary III–V Compounds (World Scientific, 1999), Vol. 2.
29. G. Mariani, Z. Zhou, A. Scofield, and D. L. Huffaker, “Direct-bandgap epitaxial core-multishell nanopillar photovoltaics featuring subwavelength optical concentrators,” Nano Lett. 13(4), 1632–1637 (2013). [PubMed]
30. Sentaurus TCAD Software Suite, Version D-2013.03, Synopsys Inc, (2013).
31. D. J. Roulston, N. D. Arora, and S. G. Chamberlain, “Modeling and measurement of minority-carrier lifetime versus doping in diffused layers of n+-p silicon diodes,” IEEE Trans. Electron. Dev. 29(2), 284–291 (1982). [CrossRef]
32. J. G. Fossum and D. S. Lee, “A physical model for the dependence of carrier lifetime on doping density in nondegenerate silicon,” Solid-State Electron. 25(8), 741–747 (1982). [CrossRef]
33. J. G. Fossum, R. P. Mertens, D. S. Lee, and J. F. Nijs, “Carrier recombination and lifetime in highly doped silicon,” Solid-State Electron. 26(6), 569–576 (1983). [CrossRef]
34. K. D. Song, T. J. Kempa, H. G. Park, and S. K. Kim, “Laterally assembled nanowires for ultrathin broadband solar absorbers,” Opt. Express 22(S3), A992–A1000 (2014). [CrossRef] [PubMed]
35. O. Demiche, M. Heiss, J. Bleuse, H. Mariette, and A. F. I. Morral, “Impact of surfaces on the optical properties of GaAs nanowires,” Appl. Phys. Lett. 97(20), 201907 (2010). [CrossRef]
36. C. C. Chang, C. Y. Chi, M. Yao, N. Huang, C. C. Chen, J. Theiss, A. W. Bushmaker, S. Lalumondiere, T. W. Yeh, M. L. Povinelli, C. Zhou, P. D. Dapkus, and S. B. Cronin, “Electrical and optical characterization of surface passivation in GaAs nanowires,” Nano Lett. 12(9), 4484–4489 (2012). [CrossRef] [PubMed]
37. N. Tajik, Z. Peng, P. Kuyanov, and R. R. LaPierre, “Sulfur passivation and contact methods for GaAs nanowire solar cells,” Nanotechnology 22(22), 225402 (2011). [CrossRef] [PubMed]
38. X. Wang, M. R. Khan, M. Lundstrom, and P. Bermel, “Performance-limiting factors for GaAs-based single nanowire photovoltaics,” Opt. Express 22(S2), A344–A358 (2014). [CrossRef]
