Surface antireflection properties of GaN nanostructures with various effective refractive index profiles

Han, Lu; Zhao, Hongping

doi:10.1364/oe.22.031907

Cited by 28 publications

(13 citation statements)

References 27 publications

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“…The absorption at the turning point of the ultraviolet short‐wavelength is lower, while the light absorption at the turning point of the visible band is higher than that of the non‐close‐packed structure. Moreover, in the long‐wave absorption region of the close‐packed nano‐cone array, the partial oscillation was observed due to the more severe interference between the reflected waves from the surface structure …”

Section: Resultsmentioning

confidence: 99%

“…The effects of the filling factor f , the height H in the size and shape of the nano‐cone on the light absorption were analyzed in the wavelength range (200‐500 nm) and the incident angle α (0°‐70°). The fill factor f is defined as the fill percentage of the bottom cross‐sectional area of the nano‐cone occupying the area of the simulated area . The nano‐cone shapes listed here all have rotational symmetry, and the simulated area is a square with a side length L .…”

Section: Structure and Simulation Methodsmentioning

confidence: 99%

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The effective light‐harvesting performance of graded compositional Al _x Ga _1−x N nano‐cone arrays photocathode for ultraviolet detector—A numerical investigation and simulation

Liu

Zhangyang

et al. 2020

Int J Energy Res

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A graded compositional Al x Ga 1−x N nanomaterial with a built-in electric field has been proposed to improve the quantum efficiency of the negative electronic affinity photocathode. When the graded compositional Al x Ga 1−x N nano-cone array is applied to the ultraviolet (UV) detector, it is necessary to improve the effective light absorption, which is high absorption in the UV short-wavelength and high sensitivity in the threshold wavelength. Therefore, the light absorption of nano-cone arrays with different feature sizes and geometrical properties is accurately calculated innovatively based on the finite-difference time-domain method. Studies show that a non-close-packed six-sided pyramid structure with a fill factor of 42.44% and a height of 1000 nm has an absorption spectrum that better satisfies the response characteristics of the UV detector. Surface reflection depends to a large extent on the transformation of the angle of incidence. The optical absorption properties of the graded compositional Al x Ga 1−x N nano-cone array provide flexibility and reference value for the improvement of the absorption coefficient and other parameters in the actual quantum efficiency experiment of the UV photocathode with built-in electric field, which can realize the highest sensitivity of various designed UV detector optical system.

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Section: Resultsmentioning

confidence: 99%

Section: Structure and Simulation Methodsmentioning

confidence: 99%

The effective light‐harvesting performance of graded compositional Al _x Ga _1−x N nano‐cone arrays photocathode for ultraviolet detector—A numerical investigation and simulation

Liu

Zhangyang

et al. 2020

Int J Energy Res

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“…13). 27 FF is calculated as the area ratio of a single pattern to the unit-cell hexagon. The FF of as-received cone patterns is 0.69.…”

Section: Cpss Etched Inmentioning

confidence: 99%

AFM and SEM Study on Crystallographic and Topographical Evolutions of Wet-Etched Patterned Sapphire Substrate (PSS): Part II. Cone-Shaped PSS Etched in H₂SO₄and H₃PO₄Mixture with Varying Volume Ratio at 230°C

Shen

Zhang

Wang

et al. 2017

ECS J. Solid State Sci. Technol.

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Here we present a systematic study on crystallographic and topographical evolutions as well as etching rates of crystallographic planes of cone-shaped patterned sapphire substrate (PSS) etched in H 2 SO 4 and H 3 PO 4 mixture with a wide range of volume ratios (H 2 SO 4 :H 3 PO 4 = 1:0, 5:1, 3:1, 1:1, 1:3, and 0:1) at 230 • C. The Miller indexes of four major exposed crystallographic planes were determined as S 1 {11 0 5}, S 3 {45 1 38}, S 4 {11 0 12}, and S 6 {11 0 8}. The etching rates of crystallographic planes follow the order S 1 > S 3 > S 4 > c plane for H 2 SO 4 and H 3 PO 4 mixtures as well as S 1 > S 6 > c plane for H 3 PO 4 . A larger volume ratio (higher H 2 SO 4 concentration) favors a higher etching rate of c-plane and conversely lower etching rates of S 1 -, S 3 -, and S 4 -planes, thus causing a larger filling factor with the largest filling factor of 0.93 obtained at the volume ratio of 5:1. This work will contribute to revealing the etching mechanism and fabricating optimized PSS for enhanced performance of light-emitting diodes. GaN-based light-emitting diodes (LEDs), as high-brightness solidstate light sources, offer attractive advantages over conventional incandescent and fluorescent lamps.1 Nevertheless, a large mismatch in the refractive index as well as the lattice constant between GaN and sapphire crystals causes difficulty with low-light extraction efficiency (LEE) and internal quantum efficiency (IQE). 2,3 To solve these problems, patterned sapphire substrate (PSS), i.e., etched sapphire substrate with artificial periodical micro/nano structures, has been proposed and popularly used commercially. The geometrical shape and dimension of PSS strongly affect the LEE and IQE of LEDs.4-6 PSSs with various geometrical shapes, usually groove, 7 circular concave, 8 cone, 9 pyramid, 10 volcano, 11 or hemispheroid, 12 have been created using dry or wet etching methods.Wet etching of PSS, usually using H 2 SO 4 and H 3 PO 4 mixture at an elevated temperature, enables crystallographic specific etching. Compared with dry etching, more sophisticated patterns can be fabricated, such as pyramids or volcanos with multiple planes showing specific slant angles. [13][14][15][16] Efforts have been devoted to investigating the crystallographic and topographical evolutions of PSS to reveal the etching mechanism and fabricating optimized PSS. 13,[15][16][17] In Part I of this series, we reported the results about crystallographic and topographical evolutions of cone-shaped PSS (CPSS) etched in the H 2 SO 4 and H 3 PO 4 mixture (H 2 SO 4 :H 3 PO 4 = 3:1 at volume ratio) at 230• C. 15We also demonstrated that atomic force microscopy (AFM), thanks to its three-dimensional (3D) topography imaging capability, is an indispensable tool for fast and reliable topographic characterization of PSS samples. However, there is still much room left for systematic studies regarding crystallographic and topographical evolutions of PSS under a wide range of etching conditions such as different mixture ratios and etchant temperatu...

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“…[ 18,19 ] The light‐absorption process of NWA can also produce a strong light‐gathering effect, which has also been proven in solar cells. [ 20,21 ] The degree of light management is very sensitive to the surface shape of the nanostructure, and light capture can be improved by changing the structural parameters. For example, for Si nanowire solar cell devices, the performance of Si arrays with a certain inclined angle is better than that of vertical arrays.…”

Section: Introductionmentioning

confidence: 99%

Enhancement of Electron Collection and Light Trapping of Inclined GaN and AlGaN Nanowire Arrays

Liu

Zhangyang

2021

Energy Tech

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The structural design of excellent absorption and electron collection is the main challenge of the nanowire array (NWA) photocathode. Herein, the light trapping and photoemission performance of GaN and graded compositional AlGaN‐inclined NWA are systematically researched. The finite‐difference time domain method (FDTD) is used to calculate the light absorption under different inclined angles and array spacings. The results show that the NWA with an inclined angle of 0.4°–0.6° has greater light‐trapping capacity, which obtains up to 97% light absorption at a wavelength of 267 nm. The inclined graded compositional AlGaN NWA with a built‐in electric field has better photoemission performance. The external electric field further improves the electron collection capacity of the NWA cathode. The inclined AlGaN NWA cathode with the best parameters θ = 0.6°, L = 180 nm, and Eout = 2 V μm−1 obtains a quantum efficiency of 47.57% and collection efficiency of 31.09%. The study of the inclined graded compositional AlGaN NWA cathode assisted by the electric field provides an effective method for further utilization of incident light and emitted electrons.

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Surface antireflection properties of GaN nanostructures with various effective refractive index profiles

Cited by 28 publications

References 27 publications

The effective light‐harvesting performance of graded compositional Al _x Ga _1−x N nano‐cone arrays photocathode for ultraviolet detector—A numerical investigation and simulation

The effective light‐harvesting performance of graded compositional Al _x Ga _1−x N nano‐cone arrays photocathode for ultraviolet detector—A numerical investigation and simulation

AFM and SEM Study on Crystallographic and Topographical Evolutions of Wet-Etched Patterned Sapphire Substrate (PSS): Part II. Cone-Shaped PSS Etched in H₂SO₄and H₃PO₄Mixture with Varying Volume Ratio at 230°C

Enhancement of Electron Collection and Light Trapping of Inclined GaN and AlGaN Nanowire Arrays

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Surface antireflection properties of GaN nanostructures with various effective refractive index profiles

Cited by 28 publications

References 27 publications

The effective light‐harvesting performance of graded compositional Al x Ga 1−x N nano‐cone arrays photocathode for ultraviolet detector—A numerical investigation and simulation

The effective light‐harvesting performance of graded compositional Al x Ga 1−x N nano‐cone arrays photocathode for ultraviolet detector—A numerical investigation and simulation

AFM and SEM Study on Crystallographic and Topographical Evolutions of Wet-Etched Patterned Sapphire Substrate (PSS): Part II. Cone-Shaped PSS Etched in H2SO4and H3PO4Mixture with Varying Volume Ratio at 230°C

Enhancement of Electron Collection and Light Trapping of Inclined GaN and AlGaN Nanowire Arrays

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About

The effective light‐harvesting performance of graded compositional Al _x Ga _1−x N nano‐cone arrays photocathode for ultraviolet detector—A numerical investigation and simulation

The effective light‐harvesting performance of graded compositional Al _x Ga _1−x N nano‐cone arrays photocathode for ultraviolet detector—A numerical investigation and simulation

AFM and SEM Study on Crystallographic and Topographical Evolutions of Wet-Etched Patterned Sapphire Substrate (PSS): Part II. Cone-Shaped PSS Etched in H₂SO₄and H₃PO₄Mixture with Varying Volume Ratio at 230°C