Optical property of hexagonal (2H) silicon crystal

Abstract

Hexagonal (2H) silicon (Si) semiconductors have excellent mechanical properties and optically diverse applications due to their structure and quasi-direct bandgap. The 2H-Si has a relatively lower direct band gap of approximately 1.69 eV at the Γ-point in comparison with that of diamond-silicon (i.e. 3.4 eV), but it is not actually a direct bandgap semiconductor. Herein, we report an optical property of wide spectrum light emission in visible and infrared ranges from grown Si crystals with a 2H structure of a 0 = 0.3824 nm, c 0 = 0.6257 nm, and c 0 /a 0 = 1.6362 corresponding to theoretical predictions and experimental results. Obtained via high-resolution transmission electron microscopy measurements, the crystal structure of the grown 2H Si possesses the only stable form of the 2H structure with the characteristic quasi-direct bandgap, achieved using mixed-source hydride vapor phase epitaxy at about 1200 • C. Raman, photoluminescence, and electroluminescence spectra, Commission International de l' Eclairage chromaticity coordinates of light emission, lattice parameters, and the quality of the crystals were evaluated and found to correspond with the predicted results. The reported material has potential applications in optoelectronics.

Insights into the growth of hexagonal Si crystals using Al-based nano absorber

“…Therefore, the Si micro single-crystal light-emitting device is considered by the spectrum of EL rather than light emission by Joule heat like a filament. The main peak at 763 nm (1.625 eV) shows a characteristic similar to about 1.70 eV theoretically predicted as a quasidirect bandgap for the characteristic of the 2H-hexagonal Si structure [5,17,20,53,[61][62][63][64]. Figure 11(j) shows the Commission international de l'Eclairage (CIE) color coordinates for visible light emission of a Si single crystal.…”

“…A mixed-source HVPE approach was used to grow the Si crystals. Mixed source HVPE is a process that involves the mixing of metal raw materials in a single well of a boat [5]. Si, Ga, and metal Al were used as the mixed source in the current study, as shown in figure 1(a).…”

“…Recently, Bakkers et al succeeded in making Si with a hexagonal crystal structure, and announced results that are expected to have unique optical, electrical, and mechanical properties as well as superconducting properties compared to conventional cubic Si [60]. Also, Ahn et al experimentally obtained lattice constants of a 0 = 3.824 Å, c 0 = 6.257 Å, and c 0 /a 0 = 1.6362 for the 2H-hexagonal Si structure [5]. Compared to the values of Pandolfi et al [54] and Rödl et al [61], wherein the relationship between the lattice reactivity and the lattice constant of the 2H-hexagonal Si structure was evaluated, the values in this paper the difference in lattice constants are a 0 = 0.4% and c 0 = 0.2%.…”

“…adsorption, reaction, and desorption. Our previous studies indicate that the growth of hexagonal Si catalyzed by Al-based nano absorbers in hydride vapor phase epitaxy (HVPE) approaches also proceeds with the formation of Al-based nanoabsorbers, adsorption of Si atoms, and desorption of Al atoms [5]. Although the reaction rate cannot be determined because it occurs too rapidly, it is presumed to be affected by the degree of exchange of charge carriers such as electrons and holes [6].…”

Recrystallization of Si Nanoparticles in Presence of Chalcogens: Improved Electrical and Optical Properties

“…This problem can be solved by switching to other silicon allotropes, many of which possess intriguing optical and electrical properties [2][3][4][5], including direct and quasidirect transitions [6][7][8][9]. For example, hexagonal Si-IV was shown to exhibit intense luminescence on the edge of the visible spectrum, with an energy of 1.5 eV [10].…”