Formation of Hierarchical Pyramid-structured Si with Nanoholes by Using Thermally Dewetted Ag Thin Films
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Formation of Hierarchical Pyramid-structured Si with Nanoholes by Using Thermally Dewetted Ag Thin Films Hanbin Lee and Hyo Jung Kim∗ School of Chemical Engineering, Pusan National University, Busan 46241, Korea (Received 11 August 2020; revised 26 August 2020; accepted 27 August 2020) Si surface texturing generally requires an etching process to improve the anti-reflection and the self-cleaning properties of the surface. Among the various etching techniques for surface texturing, the wet etching method has been widely adopted as a relatively simple and inexpensive manufacturing method. In this study, we report the effects of hierarchical pyramid-structured Si with nanoholes formed using a chemical wet etching process with thermally dewetted Ag thin films. First, alkaline etching was performed on a Si wafer to fabricate micrometer-sized random pyramid structures. Then, Ag thin film was thermally grown on the pyramid-structured Si. Finally, nanopores were formed on the random pyramid structure via metal-assisted chemical etching. The final morphology of Si was a hierarchical random pyramid structure with nanoholes, exhibiting both anti-reflection and superhydrophobicity. The average reflectance decreased to ∼4%, and the contact angle increased to 170.5◦ , allowing these surfaces to be used in various wettability-controlled optoelectronic devices, such as Si solar cells for where light trapping and self-cleaning are essential. Keywords: Anti-reflection, Superhydrophobic, Metal-assisted chemical etching, Thermally dewetted Ag DOI: 10.3938/jkps.77.598
I. INTRODUCTION Nanostructured surfaces are attracting attention for their promising applications in industry owing to their unique properties, such as superhydrophobicity and anti-reflection, which are related to anti-pollution, biocompatibility, anti-oxidation, and the improved performance of various optical and optoelectronic devices [1–4]. Therefore, considerable effort has been made to achieve nanostructured superhydrophobic and/or anti-reflection surfaces [5]. From an industrial point of view, simultaneously implementing superhydrophobic and anti-reflection functions on a Si surface is more resourceful than implementing each separately when they are integrated with other electronic components. Various methods can be used to create nanostructured surfaces on Si, and metalassisted wet chemical etching (MACE) is the most costeffective and optically interesting [6]. The MACE of Si is a controllable room temperature wet chemistry technology that uses a nanoscale metal film to etch the Si surface and produce various nanoscale and microscale surface features. MACE is used to produce black Si [7], whose surface morphology provides a graded refractive index between the Si surface and air. In addition, MACE can create a homogeneous “black Si” structure regardless of the wafer’s surface condition. In conventional MACE, the metal is placed in an etching solution and ∗ E-mail:
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pISSN:0374-4884/eISSN:1976-8524
accelerates the localized etching of the Si surface. Despite th
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