Wurtzite silicon as a potential absorber in photovoltaics: Tailoring the optical absorption by applying strain

Rödl, Claudia; Sander, Tobias; Bechstedt, F.; Vidal, Julien; Olsson, Pär; Laribi, Sana; Guillemoles, Jean‐François

doi:10.1103/physrevb.92.045207

Cited by 62 publications

(59 citation statements)

References 37 publications

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“…The corresponding spectra of the two bulk phases are also shown (left panel of Figure 3) both at IP-RPA (orange curve) and BSE (blue curve) level of approximation to verify the consistency of our results with those published in Ref. 23 As for the bulk, it is clear that also nanowires with the hexagonal-diamond phase present larger absorption in the visible region with respect to the cubic-diamond phase with a bigger overlap close to the maximum of the solar reference spectrum, possibly suggesting an improved power conversion efficiency. A graphical representation of this behavior is clearly shown in Figure 4, where a comparison between the absorption coefficients of bulk cubic and bulk hexagonal Si is presented.…”

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confidence: 86%

“…20,21 This experimental scenario suggests that exploiting polytypism in group IV NWs could be an efficient way to enhance NWs optoelectronic performances while retaining the compatibility with existent Si technology. As regards as Si NWs, recent experimental and theoretical investigations seem to confirm this prediction: cathodoluminescence measurements on hexagonal-diamond Si NWs 22 show that these structures can emit visible light with a higher efficiency than cubicdiamond NWs; on the other hand, results of ab initio calculations 23 have demonstrated that strained hexagonal-diamond bulk Si could be employed as an active layer in photovoltaic devices with absorption properties that are more favorable than those of cubic-diamond Si.…”

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confidence: 92%

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Crystal Phase Effects in Si Nanowire Polytypes and Their Homojunctions

Amato¹,

Kaewmaraya²,

Zobelli³

et al. 2016

Nano Lett.

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Recent experimental investigations have confirmed the possibility to synthesize and exploit polytypism in group IV nanowires. Driven by this promising evidence, we use first-principles methods based on density functional theory and many-body perturbation theory to investigate the electronic and optical properties of hexagonal-diamond and cubic-diamond Si NWs as well as their homojunctions. We show that hexagonal-diamond NWs are characterized by a more pronounced quantum confinement effect than cubic-diamond NWs. Furthermore, they absorb more light in the visible region with respect to cubic-diamond ones and, for most of the studied diameters, they are direct band gap materials. The study of the homojunctions reveals that the diameter has a crucial effect on the band alignment at the interface. In particular, at small diameters the band-offset is type-I whereas at experimentally relevant sizes the offset turns up to be of type-II. These findings highlight intriguing possibilities to modulate electron and hole separations as well as electronic and optical properties by simply modifying the crystal phase and the size of the junction.

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confidence: 86%

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confidence: 92%

Crystal Phase Effects in Si Nanowire Polytypes and Their Homojunctions

Amato¹,

Kaewmaraya²,

Zobelli³

et al. 2016

Nano Lett.

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“…Unfortunately, one of the biggest drawbacks for silicon's use in solar energy conversion is its indirect band gap. Theoretical [2,3] and experimental [4][5][6] efforts are looking at the properties of exotic phases of silicon and their potential as improved photovoltaic (PV) absorbers.The phase diagram of silicon [7] reveals several polytypes at elevated pressures. At a pressure of ∼11 GPa, Si-I begins to transition to Si-II which has a body-centered tetragonal crystal structure and metallic electronic structure [8].…”

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confidence: 99%

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confidence: 99%

Recovery of hexagonal Si-IV nanowires from extreme GPa pressure

Smith

Zhou

Roder

et al. 2016

Journal of Applied Physics

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We use Raman spectroscopy in tandem with transmission electron microscopy and DFT simulations to show that extreme (GPa) pressure converts the phase of silicon nanowires from cubic (Si-I) to hexagonal (Si-IV) while preserving the nanowire's cylindrical morphology. In situ Raman scattering of the TO mode demonstrates the high-pressure Si-I to Si-II phase transition near 9 GPa. Raman signal of the TO phonon shows a decrease in intensity in the range 9 to 14 GPa. Then, at 17 GPa, it is no longer detectable, indicating a second phase change (Si-II to Si-V) in the 14 to 17 GPa range. Recovery of exotic phases in individual silicon nanowires from diamond anvil cell experiments reaching 17 GPa is also shown. Raman measurements indicate Si-IV as the dominant phase in pressurized nanowires after decompression. Transmission electron microscopy and electron diffraction confirm crystalline Si-IV domains in individual nanowires. Computational electromagnetic simulations suggest that heating from the Raman laser probe is negligible and that near-hydrostatic pressure is the primary driving force for the formation of hexagonal silicon nanowires.Silicon is the second most abundant element in the Earth's crust [1] and the foundation of the modern electronics industry. It is used for integrated circuits in information technology and as an energy conversion material in photovoltaics. Unfortunately, one of the biggest drawbacks for silicon's use in solar energy conversion is its indirect band gap. Theoretical [2,3] and experimental [4][5][6] efforts are looking at the properties of exotic phases of silicon and their potential as improved photovoltaic (PV) absorbers.The phase diagram of silicon [7] reveals several polytypes at elevated pressures. At a pressure of ∼11 GPa, Si-I begins to transition to Si-II which has a body-centered tetragonal crystal structure and metallic electronic structure [8]. As pressure increases past approximately 15 GPa, Si-V begins to emerge with a primitive hexagonal phase [9][10][11]. But neither Si-II nor Si-V are stable at atmospheric pressure and, therefore, have not been observed experimentally outside of high pressures. Si-III (body-centered cubic) and Si-IV (diamond hexagonal), however, are stable at atmospheric pressure and have been synthetisized [4,12,13] as well as recovered from high-pressure phase transitions [14,15]. While Si-III is a semimetal [14] and could have applications in electronics, Si-IV is a semiconductor with a reported indirect band gap near 0.8-0.9 eV and direct transition at 1.5 eV [13]. The direct transition for Si-IV makes * peterpz@uw.edu FIG. 1. Schematic of the diamond anvil cell (DAC) and components for Raman scattering measurements. A holographic laser bandpass (HLB) filter is used to pass the 532 nm Raman probe into a 50x objective which focused the beam into DAC. Nanowire Raman scattering and ruby photoluminescence were collected with the same objective and sent to a spectrometer or CCD for imaging. A 532 nm notch filter (NF) was used to eliminate strong Rayleigh scat...

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“…Это позволило бы использовать кремний -основной материал современ-ной микроэлектроники -в оптоэлектронных интегральных схемах нового поколения, так как обычный алмазоподобный кремний из-за своей непрямозонной структуры обладает низкой излучательной способностью. Теоретические предсказания [1,2] и некоторые экспери-ментальные работы [3] дают основания предполагать, что по крайней мере некоторые гексагональные фазы Si, даже если они не обладают прямозонной энергетической структурой, способны обеспечить более эффективное возбуждение люминесценции по сравнению с алмазопо-добной кубической фазой.…”

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Формирование Гексагональной Фазы Кремния 9R При Ионной Имплантации

Королев¹,

Никольская²,

Кривулин³

et al. 2017

Письма В Журнал Технической Физики

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С помощью метода просвечивающей электронной микроскопии в приграничном слое кремния структуры SiO2/Si, подвергнутой ионной имплантации и термической обработке, обнаружено образование включений гексагонального кремния (политип 9R). Образование гексагональной фазы обусловлено механическими напряжениями, возникающими в гетерофазной системе в процессе ионной имплантации. DOI: 10.21883/PJTF.2017.16.44937.16852

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Wurtzite silicon as a potential absorber in photovoltaics: Tailoring the optical absorption by applying strain

Cited by 62 publications

References 37 publications

Crystal Phase Effects in Si Nanowire Polytypes and Their Homojunctions

Crystal Phase Effects in Si Nanowire Polytypes and Their Homojunctions

Recovery of hexagonal Si-IV nanowires from extreme GPa pressure

Формирование Гексагональной Фазы Кремния 9R При Ионной Имплантации

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