Photoelectrochemical Etching Of Silicon Research Articles

Macroscale Transformation Optics Enabled by Photoelectrochemical Etching.

Photoelectrochemical etching of silicon can be used to form lateral refractive index gradients for transformation optical devices. This technique allows the fabrication of macroscale devices with large refractive index gradients. Patterned porous layers can also be lifted from the substrate and transferred to other materials, creating more possibilities for novel devices.

Macroporous silicon and its application in sensing

Abstract Periodic silicon nanostructures can be used for different kinds of gas sensors depending on the analyte concentration. First, we present an optical gas sensor based on the classical non-dispersive infrared technique for ppm-concentration using ultra-compact photonic crystal gas cells (Pergande et al., 2011) [1] . It is conceptually based on low group velocities inside a photonic crystal gas cell and anti-reflection layers coupling light into the device. Secondly, we report on silicon nanotip arrays (Gesemann et al., 2011) [2] , suitable for gas ionization in ion mobility microspectrometers (micro-IMS) having detection ranges in principle down to the ppt-range. Such instruments allow the detection of explosives, chemical warfare agents, and illicit drugs, e.g., at airports. Third of all, we describe the thermal emission properties of heated silicon photonic crystals (Gesemann et al., 2010) [3] , revealing a photonic stop gap effect or strong silicon oxide emission, depending on the setup. All silicon microstructures have been fabricated by photo-electrochemical etching of silicon.

Fabrication of one-dimensional photonic crystals by photoelectrochemical etching of silicon

The conditions of formation of deep periodic trenches by photoelectrochemical etching of n-Si (100) with linear seeds on the surface are analyzed. Criteria for the proper choice of the period of seed grooves and the etching current density in relation to the doping level of the substrate are formulated. Corrugation of walls is a characteristic feature of the obtained structures; this corrugation is caused by traces of merged macropores. Atomic-force microscopy is used to study roughness of the side-walls in relation to the etching conditions; the current density at which one can obtain the smoothest side-walls is determined. The roughness of the side walls in structures with periods of 7 and 9 μm on Si with the resistivity of 15 Ω cm amounts to ∼40 nm. It is shown that additional treatment of the structures in alkaline solutions can decrease the side-wall roughness by approximately a factor of 2.

Optical properties of one-dimensional photonic crystals fabricated by photo-electrochemical etching of silicon

The optical properties of one-dimensional photonic crystals (1D PCs), fabricated by electrochemical etching of periodic wall arrays on n-type (100) Si substrates, are investigated in this study. Several 1D PCs were fabricated with lattice periods varying from 4 to 7 μm and with trench depths in the range 160–210 μm. In-plane reflection spectra of the photonic structures at different depths were registered over a wide spectral range of 1.5–15 μm using Fourier Transform Infra-Red (FTIR) micro-spectroscopy. Some of the features observed in the reflection spectra of the structures investigated are believed to be as a result of interface roughness. A corrugated side-wall surface, an artifact of the fabrication technique, results in the degradation of optical reflection characteristics, principally mainly in the near IR spectral range, and the emergence of optical anisotropy. As a result of the periodicity, modulation of the reflection spectra, that is, the difference between the maxima and minima of the interference fringes, reached a value of 95% in the mid-infrared. The optical properties of the structures investigated indicate that they show promise for microphotonics applications.

Fabrication of self‐aligned gated silicon microtip array using electrochemical silicon etching

AbstractIn this paper we report a new approach to fabricate gated silicon microtip arrays for field emission applications using a single mask process. The key role in the fabrication process is played by the photoelectrochemical etching of silicon in HF‐based electrolytes. This technique is here exploited to produce highly uniform silicon microtip arrays. The fabrication process is detailed and the dependence of the tip geometry on the electrochemical etching parameters is discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A thick silicon dioxide fabrication process based on electrochemical trenching of silicon

Thick silicon dioxide films have recently been proposed for sensor applications (thermal isolation in high-temperature sensors, gas sensors, etc.). In this paper a simple and low cost method to produce thick silicon dioxide layers (thickness of several tens of microns) is reported. The process is based on the photoelectrochemical etching of silicon in HF solution. This technique is here used to produce deep high aspect ratio regular trenches, which are then completely oxidized to obtain a thick silicon dioxide layer.

Effect of irradiant wavelength during porous silicon formation

Photoelectrochemical etching of silicon using light assistance of various wavelengths has been studied. As the etching process proceeds, a blueshift is noted in the photoluminescence spectra. However, after a certain period of etching, under a fixed current density, a saturation point is reached, below which no further shift to higher energies is detected. This cutoff point occurs at approximately 2 eV, even if a much higher energy irradiant light source is used during the formation process. These results provide strong evidence for the surface-state mechanism of luminescence and render the pure quantum confinement model unlikely.

Photoelectrochemical etching of silicon

The state of the art of electrochemical and photoelectrochemical etching of silicon in HF is reviewed, which leads to interesting and novel surface morphologies. New results are presented concerning the change of electronic properties engendered by photoelectrochemical etching and the use of such modified surfaces as rectifying interfaces. It is emphasized that PEC-etching is thus a major new area of application of photoelectrochemistry.

Micromachining of three-dimensional silicon structures using photoelectrochemical etching

Photoelectrochemical etching of silicon in hydrofluonc acid solutions is proposed as a method for realising three-dimensional sensor and actuator elements. It is shown that high selectivity in etch rates between illuminated and dark areas can be obtained by a proper electrochemical bias. This can be implemented with an inert metal electrode, e.g. platinum. The technique could be useful for fabrication of beam and membrane structures for holographic gratings and for maskless small-volume production.