Silicon is an excellent material for microelectronics and integrated photonics1–3 with untapped potential for mid-IR optics4. Despite broad recognition of the importance of the third dimension5,6, current lithography methods do not allow fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realised with techniques like reactive ion etching. Embedded optical elements, like in glass7, electronic devices, and better electronic-photonic integration are lacking8. Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1 µm-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has a different optical index than unmodified parts, which enables numerous photonic devices. Optionally, these parts are chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface, i.e., “in-chip” microstructures for microfluidic cooling of chips, vias, MEMS, photovoltaic applications and photonic devices that match or surpass the corresponding state-of-the-art device performances.

We present the feasibility of integrating substoichiometric molybdenum oxide (MoOx) as hole‐selective rear contact into the production sequence of industrial scale p‐type crystalline silicon (c‐Si) solar cells. Thin films of MoOx are deposited directly on p‐type c‐Si by thermal evaporation at room temperature. It is found that Ag/MoOx/p‐type c‐Si rear contact structure exhibits low contact resistivity and modest surface recombination current density. The attained peak efficiency (η) of the fabricated solar cells is 17.65% with Voc of 626 mV, Jsc of 36.8 mA/cm2, and fill factor (FF) of 76.63%. Next, a complete loss analysis of a MoOx/p‐type Si heterojunction solar cell is carried out for the first time by using Quokka simulation software that employs characteristics of different layers which constitute the fabricated solar cell. Based on this loss analysis, the dominant loss mechanisms are defined and a roadmap to attain the desired highest possible efficiency from industrial scale p‐type c‐Si solar cells with full‐area MoOx hole‐collecting rear contact is explored.

Summary Substitution of highly doped layers with conventional transparent conductive electrodes as carrier collecting and selective contacts in conventional crystalline silicon (c‐Si) solar cell configurations is crucial in increasing affordability of solar cells by lowering material costs. In this study, oxide/metal/oxide (OMO) multilayers featuring molybdenum oxide (MoOx) and silver (Ag) thin films are developed by thermal evaporation technique, as dopant‐free hole transport transparent conductive electrodes (HTTCEs) for n‐type c‐Si solar cells. Semidopant‐free asymmetric heterocontact (semi‐DASH) solar cells on n‐type c‐Si utilizing OMO multilayers are fabricated. The effect of outer MoOx layer thickness and Ag deposition rate on the photovoltaic characteristics of the fabricated semi‐DASH solar cells are investigated. A comparison of front side pyramid textured and flat surface solar cells is performed to optimize the optical and electrical properties. Highest efficiency of 9.3% ± 0.2% is achieved in a pyramid textured semi‐DASH c‐Si solar cell with 15/10/30 nm of HTTCE structure.

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molecular identification technique that originates from the marriage of the high molecular specificity of Raman spectra and the ultra-high signal amplification property of plasmonic metal nanostructures. [1][2][3][4][5][6][7][8] SERS technique shows great promise in a wide variety of fields including biosensing, gas phase chemical detection, and single molecule detection. [9][10][11][12][13][14][15] Besides the high and spatially uniform enhancement factor (EF); chemical stability, reproducibility, precision, and fast fabrication in large areas with less debris are demanded for ideal SERS substrates. [16,17] Even though metallic nanoparticles exhibit high SERS EFs, they do not offer proper particle stability, and use in large areas. [18][19][20] Femtosecond laserbased techniques offer the fabrication of highly sensitive SERS substrates with low detection limits. [21][22][23] On the contrary to wet chemical synthesis procedures, uniformity, robustness, and reproducibility are provided by laser-assisted periodic nanostructures. Without any lithographic processes, the number of processes to fabricate highly sensitive SERS sensing devices is also reduced. [24][25][26] Generation of laser-induced periodic surface structuring (LIPSS) by using the direct laser writing technique with ultrafast (femtosecond -fs) laser sources [27] is a fast and low-cost method compared to other well-established techniques such as laser interference lithography, [28] photolithography, electron beam lithography, and nanoimprint lithography. [29] Controlling the irradiation wavelength, the number of pulses on the spot, the polarization direction of the beam, repetition rate, the fluence of the ultrafast laser, and the scanning speed leads to the formation of the nano ripples on semiconductors and metals. [30][31][32][33][34] Nanoripples formed by an fs-laser can be classified into two, Low Spatial Frequency LIPSS (LSFL) and High Spatial Frequency LIPSS (HSFL). [35] Furthermore, both types of structures, formed on metal and semiconductor surfaces, have potential benefits as a SERS substrate as well. [36][37][38][39][40][41] LSFL structures exhibit periods close to irradiation wavelength, meanwhile; HSFL structures have periods smaller than half of the irradiation wavelength. [35,[42][43][44][45][46] The formation mechanism of LSFL structures was first introduced by Sipe theory in 1982. [47] With the appropriate energy exposure and the high number of free carriers on the surface, the dielectric A novel method of fabricating large-area, low-cost surface-enhanced Raman spectroscopy (SERS) substrates is introduced which yields densely nanostructured surfaces utilizing laser-induced periodic surface structuring (LIPSS) of crystalline silicon (Si). Two different interaction regimes yield low spatial frequency (LSFL) and high spatial frequency (HSFL) LIPSS patterns. Nanostructuring of Si surface is followed by deposition of a thin noble metal layer to complete the fabrication procedure. A 50-70 nm thick Ag layer is shown to maximize the SERS perform...