Reflectance Characteristics of Silicon Surface Fabricated with the Arrays of Uniform Inverted Pyramid Microstructures in UV-Visible Range

Abstract

In this paper, inverted pyramidal microstructures are designed and fabricated on silicon (Si) surface. The characteristics of surface reflectance are simulated using two-dimensional (2D) finite-difference time-domain (FDTD) method by varying the spacing (S) and width (W) of the pyramidal microstructures. The results showed that the effect of S is more significant compared to W where the reflectance of the irradiated light has been increased gradually with the increase of S from 0 to 3 µm, and the difference is around 9.6%. Due to the etching constraint, S= 3 µm is chosen for the fabrication. Textured structure is fabricated by the anisotropic etching of tetramethyl-ammonium hydroxide (TMAH) with additional of isopropyl alcohol (IPA). Long etching time of 120 min is required to form uniform arrays of pyramidal microstructures with smooth and well-terminated four sidewalls at (111) plane. Due to the undercut etching under SiO 2 mask, it results to the formation of slightly larger W and smaller S in the fabricated structures. The measured average reflectance in UVvisible range for the Si with inverted pyramidal microstructures is very low down to 10.4%. The discrepancy between the measured and simulated values is speculated to be due to the use of 2D FDTD instead of three-dimensional (3D) FDTD. ABSTRAKDalam kertas ini, mikrostruktur piramid songsang Si bersaiz mikro telah direka bentuk dan difabrikasi di atas permukaan silikon (Si). Ciri pantulan permukaan telah disimulasi menggunakan kaedah domain-masa perbezaan-terhingga (FDTD) dua-dimensi (2D) dengan membezakan jarak dan lebar mikrostruktur piramid. Data menunjukkan kesan jarak (S) adalah lebih ketara jika dibandingkan dengan kesan lebar (W) terhadap pantulan permukaan. Pantulan cahaya yang disinarkan telah meningkat secara beransur-ansur dengan peningkatan S daripada 0 kepada 3 µm dan perbezaan adalah sekitar 9.6%. Disebabkan kekangan punaran, S= 3 µm telah dipilih untuk difabrikasi. Tekstur telah difabrikasi dengan cara punaran anisotropik oleh tetra metil ammonium hidroksida (TMAH) berserta campuran alkohol isopropil (IPA). Punaran pada tempoh yang lama iaitu 120 min diperlukan untuk membentuk jajaran mikrostruktur piramid yang seragam dengan empat sisi tepi pada satah (111) yang licin berserta penamatan yang baik. Disebabkan potongan bawah punaran di bawah topeng SiO 2 , ia membentuk W yang sedikit lebih besar dan S yang lebih kecil bagi struktur yang telah difabrikasi. Purata pantulan dalam julat UV-nampak yang telah diukur bagi Si dengan mikrostruktur piramid songsang adalah sangat rendah iaitu 10.4%. Percanggahan antara nilai yang diukur dengan nilai yang disimulasi telah dispekulasi disebabkan penggunaan FDTD 2D dan bukannya FDTD tiga-dimensi (3D).

Effect of Various Wafer Surface Etching Processes on c-Si Solar Cell Characteristics

“…In the etching process using KOH and MACE, a nano-structured pyramid is formed on a wafer surface-etched with KOH using a Ag metal catalyst. After forming a pyramid structure on the wafer surface using the five methods, the average reflectance of the wavelength of 400~1000 nm was measured with a UV/VIR spectrometer, and the pyramid structure was confirmed through field emission scanning electron microscope (FE-SEM) images [20]. In order to analyze the characteristics according to the pyramid structure when fabricating the wafer surface-etched through five methods into cells, an emitter formation process was performed using a furnace.…”