Stable hexagonal-wurtzite silicon phase by laser ablation

Zhang, Yan; Iqbal, Zafar; Vijayalakshmi, S.; Grebel, Haim

doi:10.1063/1.125140

Cited by 51 publications

(42 citation statements)

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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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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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Recovery of hexagonal Si-IV nanowires from extreme GPa pressure

Smith

Zhou

Roder

et al. 2016

Journal of Applied Physics

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“…Figure 1 shows the atomic structure of the relaxed WZ-Si and the corresponding band-structure. The cell parameters and band gap properties of WZ-Si obtained from the present work are listed in Table I, together with data reported in the literature [12,22,23,24]. The relaxed WZ-Si is an indirect band-gap semiconductor with a calculated band gap of 0.47 eV between the valence-band maximum (VBM) and the conduction-band minimum (CBM) at M, and a direct band gap of 1.02 eV at Γ, respectively.…”

Section: A Balanced Structure Of Wuzite-simentioning

confidence: 99%

Band Gap Engineering of Wurtzite Silicon by Uniaxial Pressure

Cui¹

2017

IJIRCST

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Abstract-Electronic properties of wurtzite silicon (WZ-Si) are investigated by first-principle calculation. It is found that WZ-Si is an indirect band-gap semiconductor at ambient condition. A uniaxial strain along the c-direction can reduce the direct energy gap at Γ significantly. Calculated pressure needed to compress WZ-Si is not too high, which shows strained WZ-Si would be potential in practical use. The effective mass of electron is found strongly dependent on strain which could be used to tailor the transport properties.

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“…w-Si material is rarely studied by spectroscopic measurements, because it cannot be obtained in a stable phase. Zhang et al (Zhang et al, 1999) produced stable w-Si phase by laser ablation. Its identification by electron diffraction has been confirmed by micro Raman spectroscopy.…”

Section: Stabilization Of Wurtzite Simentioning

confidence: 99%