Photoelectrochemistry of silicon in HF solution

Abstract

Photoelectrochemical, photoelectrocatalytic and electrochemical processes of silicon anodic oxidation and hydrogen evolution in aqueous HF solution are discussed in terms of thermodynamic stability of Si, oxides SiO, SiO 2 and Si surface hydrides. It is shown that photoelectrochemical oxidation of n-type low resistivity silicon to SiO 2 is catalyzed by Si + photo-hole formation, whereas in the case of p-type Si, the feasibility of this reaction is predetermined by p-type conductivity. It is suggested that anodic oxidation of Si goes through the stage of SiO oxide formation and its subsequent oxidation to SiO 2. Such mechanism accounts for chemical inertness of Si phase in HF solutions as well as for selective, anisotropic and isotropic etching of Si within E ranges from-0.5 V to 0.35 V, 0.35-0.8 V, and E > 0.8 V, respectively. Hydrogen evolution reaction (HER) on Si surface proceeds at very large overpotential (≥ 0.5 V) through the stage of surface Si hydride formation: Si + H 2 O + e − → (SiH) surf + OH − (the rate determining step) and (SiH) surf + H 2 O + e − → Si + H 2 + OH −. Illumination related effects of surface reactions relevant to selective and anisotropic etching and nano/microstructuring of Si surface are discussed. Keywords Methods of nanofabrication and processing • Nanostructured materials in electrochemistry • Semiconductor materials in electrochemistry • Thermodynamics of solutions • HER • electrodissolution of Si

Control of surface charge for high‐fidelity nanostructuring of materials

“…In practical implementation of the proposed charge removal method, the placement of three‐dimensional electrodes above the surface of the sample can be envisaged for collection of electrons freed from the surface by UV illumination; some of the electrons can be required for compensation of the surface positive charge due to ion milling. Also, chemical modifications can be expected due to photochemical reactions; the equivalence of electrical potential (or charging) and light‐induced absorption for surface chemical modifications has been recently demonstrated in Si . The proposed method should be useful for applications in plasmonics and sensing where nano‐grooves with sub‐20 nm resolution have to be made for strong light enhancement and for texturing of TiO 2 solar cells for solar hydrogen generation .…”

“…7, No. 6 (2013) 1053 potential (or charging) and light-induced absorption for surface chemical modifications has been recently demonstrated in Si [25]. The proposed method should be useful for applications in plasmonics and sensing where nano-grooves with sub-20 nm resolution have to be made for strong light enhancement [5] and for texturing of TiO 2 solar cells for solar hydrogen generation [26].…”

Black-Si as Photoelectrode

“…Also, an increase of surface area of Black-Si due to its nanotexture [16] is another advantage for a large current operation of photo-electrochemical cell. Complex pathways of (photo)electrochemical modification of Si are possible in acidic solutions due to the different valence states of Si [17]. In basic solutions, Si is usually stable at room temperature [18], hence, is promising as an electrode.…”

Towards Safer Primers: A Review

“…Porous silicon is created by electrochemical etching and is a highly tunable system for ignition properties and integration into semiconductor based devices [88,89]. Since silicon can be in very different valence states at different oxidation levels, that can be exploited in (photo-)electro-chemical etching methods to deliver different surface morphologies [90]. Surface nano-/micro-roughening can be electrochemically controlled on laser-ablated surfaces of Si [91].…”