Alkali Etchant Research Articles

Honeycomb-like gallium nitride prepared via dual-ion synergistic etching mechanism using amino acid as etchant

Amino acid, taking the glycine (Gly) for example, was used for the first time as etchant to assemble honeycomb-like structure on gallium nitride (GaN) by photo-electrochemical etching (PECE) technique. Conspicuously, a novel dual-ion dissolution etching mechanism model was proposed, of which could extensively promote to almost all amino acids and their derivatives as well. Importantly, double ions of amino acids are of a synergistic effect with amino and carboxyl groups, which facilitate the generation and stabilization of the honeycomb-like structure with uniform pore size (~26.5 nm), high pore density and superior reusability, and the intermolecular hydrogen bonding can maintain the honeycomb-like structure without being destroyed. From the point of view of costs, scale-up production, biocompatibility and environmental friendliness, Gly has obvious advantages over the traditional strong acid and alkali etchant.

Field Emission Properties of Polymer Graphite Tips Prepared by Membrane Electrochemical Etching.

This paper investigates field emission behavior from the surface of a tip that was prepared from polymer graphite nanocomposites subjected to electrochemical etching. The essence of the tip preparation is to create a membrane of etchant over an electrode metal ring. The graphite rod acts here as an anode and immerses into the membrane filled with alkali etchant. After the etching process, the tip is cleaned and analyzed by Raman spectroscopy, investigating the chemical composition of the tip. The topography information is obtained using the Scanning Electron Microscopy and by Field Emission Microscopy. The evaluation and characterization of field emission behavior is performed at ultra-high vacuum conditions using the Field Emission Microscopy where both the field electron emission pattern projected on the screen and current–voltage characteristics are recorded. The latter is an essential tool that is used both for the imaging of the tip surfaces by electrons that are emitted toward the screen, as well as a tool for measuring current–voltage characteristics that are the input to test field emission orthodoxy.

Migration behavior of alkali and alkaline-earth cations in soda-lime silicate glass surface by electrical nanoimprint

One dimensional pattern of 500nm period was formed on a soda-lime silicate glass by the electrical nanoimprint below the glass transition temperature. The imprinted glass surface was analyzed using a transmission electron microscopy and an energy-dispersive X-ray spectroscopy with the cryogenic system. The concentrated parabolic layers of Ca2+ and Mg2+ were formed separately in the Na+ deficient layer. The deficient area both of such alkali and alkaline-earth cations was preferentially removed in an alkali etchant, resulting the enhancement of the aspect ratio of the one-dimensional relief pattern. Therefore, the distribution control of alkaline-earth cations was important for the fabrication of sub-micron scale patterns with high aspect ratio on the glass surface.

KOH anisotropic etching of Si wafers for light-emitting diode electrode arrays

The formation of Si trenches with anisotropic wet etching of (100) Si wafers for light-emitting diode electrode arrays has been investigated. An alkali etchant, potassium hydroxide (KOH), was used as the anisotropic etchant for the Si etching in this study. Experimental results show that the KOH etching process not only etches the Si surface, but also etches the SiO2 film on the wafer surface. Electrode arrays of 25 columns by 25 rows, providing a total of 625 trenches in the Si wafer, were produced with well-controlled anisotropy. Finally, Silvaco TCAD software was used to simulate the thermal power variation of the LED die in the Si trench. Heat distribution simulation analysis showed that this design improves the heat dissipation problem in subsequent manufacturing processes, such as assembly and packaging.

Efficiency improved by acid texturization for multi-crystalline silicon solar cells

In this paper, we will show that efficiency of multi-crystalline silicon (mc-Si) solar cells may be improved by acid texturization. In order to enhance overall efficiency of mc-Si for solar-cell applications, the surface treatment of texturization with wet etching using appropriate solutions can improve incident light into the cell. Alkali etchant cannot produce uniformly textured surface to generate enough open circuit voltage ( V OC) and high efficiency of the mc-Si due to the unavoidable grain randomly oriented with higher steps formed during etching process. Optimized acid etching conditions can be obtained by decreasing the reflectance ( R) for mc-Si substrate below levels generated by alkali etching. Short-circuit current ( I SC) measurements on acid textured cells reveal that current gain can be significantly enhanced by reducing reflection. The optimal acid etching ratio HF:HNO 3:H 2O = 15:1:2.5 with etching time of 60 s and lowering 42.7% of the R value can improve 112.4% of the conversion efficiency ( η) of the developed solar cell. In order to obtain more detailed information of different defect region, high-resolution light beam induced current (LBIC) is applied to measure the internal quantum efficiency (IQE) and the lifetime of minority carriers. Thus, the acid texturing approach is instrumental to achieve high efficiency in mass production using relatively low-cost mc-Si as starting material with proper optimization of the fabrication steps.

등방성 에칭용액을 이용한 다결정 실리콘의 표면조직화

Surface Texturing is very important process for high cell efficiency in crystalline silicon solar cell. Anisotropic texturing with an alkali etchant was known not to be able to produce uniform surface morphology in multi-crystalline silicon (mc-Si), because of its different etching rate with random crystal orientation. In order to reduce surface reflectance of mc-Si wafer, the general etching tendency was studied with HF/HNO₃/De-ionized Water acidic solution. And the surface structures of textured mc-Si in various HF/HNO₃ ratios were compared. The surface morphology and reflectance of textured silicon wafers were measured by FE-SEM and UVvisible spectrophotometer, respectively. We obtained average reflectance of 16~19% for wavelength between 400 ㎚ and 900 ㎚ depending on different etching conditions.

Comparative study of different approaches of multicrystalline silicon texturing for solar cell fabrication

Alkali etchant cannot produce uniformly textured surface to generate satisfactory open circuit voltage as well as the efficiency of the multi-crystalline silicon (mc-Si) solar cell due to the unavoidable grain boundary delineation with higher steps formed between successive grains of different orientations during alkali etching of mc-Si. Acid textured surface formed by using chemicals with HNO 3–HF–CH 3COOH combination generally helps to improve the open circuit voltage but always gives lower short circuit current due to high reflectivity. Texturing mc-Si surface without grain boundary delineation is the present key issue of mc-Si research. We report the isotropic texturing with HF–HNO 3–H 2O solution as an easy and reliable process for mc-Si texturing. Isotropic etching with acidic solution includes the formation of meso- and macro-porous structures on mc-Si that helps to minimize the grain-boundary delineation and also lowers the reflectivity of etched surface. The study of surface morphology and reflectivity of different mc-Si etched surfaces has been discussed in this paper. Using our best chemical recipe, we are able to fabricate mc-Si solar cell of ∼14% conversion efficiency with PECVD AR coating of silicon nitride film. The isotropic texturing approach can be instrumental to achieve high efficiency in mass production using relatively low-cost silicon wafers as starting material with the proper optimization of the fabrication steps.

Chemical etching‐induced defects in n‐type ZnSe crystal grown by physical vapor transport

We have found with deep level transient spectroscopy that chemical etching induced two isolated point defects, E1(0.26–0.31) and E2(0.20), in the near-surface region of n-type ZnSe single crystals. The etching effect on the traps in Br-doped ZnSe bulk crystals was studied by using 5% Br-methanol solution, and then the E1 trap density increased with the chemical etching time, and reached to maximum value of 5.3 × 1013 cm–3. The E1 trap was obtained in the samples etched in some kinds of acid solutions, Br-methanol solution, HCl, and HBr, but did hardly in NaOH alkali etchant. These results suggest that the E1 trap is induced during the chemical etching and diffuse into the interior of the crystals. From above etching effects, we propose a tentative identification that E1 and E2 traps arise from two kinds of hydrogen related defects.

Transmission Electron Microscopic Investigation of the Morphology of High-Speed Spun Poly(Ethylene Terephthalate) Fibers

Permanganic etching was performed on high-speed spun (HSS) and regular fibers of poly(ethylene terephthalate) (PET), and their surface morphologies were investigated via the two-stage carbon replica method using a transmission electron microscope (TEM). The HSS PET fibers, with disordered amorphous regions, showed peculiar surface morphology; many small warts corresponding to the pits of etched disordered amorphous regions were observed. Such unevenness, however, was hardly observed on the surface of the permanganic-etched regular PET fibers, with well-oriented amorphous regions, or on the surface of alkali-etched HSS PET fibers. The permanganic etchant removed the disordered amorphous regions more preferentially compared with the alkali etchant.

Influence of anisotropic etching on the mechanical strength of single-crystal silicon wafers

The influence is investigated of silicon wafer treatment in the alkali etchant with surface orientation close to planes (111), (100), and (110) on the magnitude of mechanical strength. It is shown that the dependence of the mechanical strength of silicon wafers on the etch time in the alkali etchant irrespective of orientation planes has a complex characteristics, namely: with the increase of etch time the mechanical strength increases, reaches its maximum value and with the further etch time growth it decreases and acquires values less than the ultimate strength. The analysis of the experimental results shows a close connection between the mechanical strength changes and the microstructure of the distorted layer of the silicon wafer surface. [Russian Text Ignored].

Utilization of the selectivity of dissolution of glassy chalcogenide semiconductor films in the formation of passive integrated-optics components

A study was made of the influence of the stoichiometry profile of films in the As–S system on the dynamics of their dissolution in an alkali etchant. It was found that the surface changes in the stoichiometry of As–S films exposed to laser radiation influenced the rate of dissolution. The dynamics of dissolution of glassy chalcogenide semiconductor films with given stoichiometry profiles was analyzed and methods of formation of grating structures with a high diffraction efficiency were considered.