Effects of Photonic Band Structure and Unit Super-Cell Size in Graded Photonic Super-Crystal on Broadband Light Absorption in Silicon

Abstract

The newly discovered graded photonic super-crystal (GPSC) with a large size of unit cell can have novel optical properties that have not been explored. The unit super-cell in the GPSC can be designed to be large or small and thus the GPSC can have no photonic band gap or several gaps. The photonic band structures in Si GPSC can help predict the light absorption in Si. Photonic resonance modes help enhance the absorption of light in silicon; however, photonic band gaps decrease the absorption for light with a large incident angle. The Si device patterned in GPSC with a unit super-cell of 6a × 6a (a is a lattice constant in traditional photonic crystal) has a broadband high absorption with strong incident-angular dependence. The device with the unit super-cell of 12a × 12a has relatively low light absorption with weak incident-angle dependence. The Si GPSC with a unit super-cell of 8a × 8a combines both advantages of broadband high absorption and weak dependence of absorption on the incident angle.

Generation of over 1000 Diffraction Spots from 2D Graded Photonic Super-Crystals

“…The diffraction pattern indicates that GPSC can be formed with very high precision, and the GPSC structure show not only simple periodicity but also those with tens of different in size "atoms" or "molecules" in a unit cell. Simulations predicted a broadband light trapping enhancement in solar cells [16,27] or an enhanced broadband extraction efficiency in OLEDs [15,28] when solar cells or OLEDs are patterned in GPSC, respectively. These experimentally observed fractional diffraction orders help understand the mechanism of broadband enhancement in solar cells or OLEDs patterned in GPSC and promote GPSC applications in these devices.…”

“…GPSC has dual period and even dual symmetry: The square lattices in GPSC have a small period while graded regions have their own symmetry and period [12][13][14]. GPSCs can be used to enhance the broadband light trapping in an Si solar cell, broadband light extraction from organic light emitting diode, and to form a resonance cavity at the boundary of graded and less-graded regions [15][16][17]. By incorporating disorders in the location and radii of the holes in the 2D photonic crystal, topological properties appear in the photonic crystal [18,19].…”

Photonic Band Gaps and Resonance Modes in 2D Twisted Moiré Photonic Crystal

“…A change of the refractive index in dielectric materials in twisted photonic crystal will not only shift the central frequency of band gap but also change the band gap size. For the simulation of the photonic band gap of twisted photonic crystals in dielectric materials with a varying refractive index at different wavelengths, a MEEP program should be used [38,47]. However, the MEEP program is not good at simulating the photonic band structure at low frequencies.…”

Broadband Absorption in Patterned Metal/Weakly-Absorbing-Spacer/Metal with Graded Photonic Super-Crystal

“…A recently discovered graded photonic super-crystal (GPSC) can have a very large unit super-cell with two sets of motifs: the rod size (or hole size) decreases gradually along one direction in one set of motifs while the other set increases their sizes gradually [32][33][34][35][36][37][38][39][40][41]. The spatially gradient motifs are arranged on a square lattice with a small period, and graded regions in GPSC have a large period and their own symmetry.…”

“…The spatially gradient motifs are arranged on a square lattice with a small period, and graded regions in GPSC have a large period and their own symmetry. The GPSC can have dual period and dual symmetry [32][33][34][35][36][37][38][39][40][41][42]. Due to the gradient two-set motifs in the unit supercell, GPSCs can be used to enhance the broadband light trapping in an Si solar cell and broadband light extraction from an organic light emitting diode [37][38][39][40][41].…”