The effect of etching time on the CdZnTe surface

The surface quality of CdZnTe plays an important role in the performance of sensors based on this material. In this paper the effect of chemical etching on Cd_0.9Zn_0.1Te sensor performance was examined. Sample surfaces were treated with the same concentration 2% Br-MeOH for different etching times (30 s, 2, 4, 6, 8 min). The surfaces were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and I-V Measurement. These results demonstrate that the best surface quality can be obtained by chemical etching for 30 s. Under these experimental conditions, the surface composition Te/Cd + Zn approaches 1, the roughness is lower than 3 nm, and the leakage current shows a value lower than 10 nA.     

Removal of scratch on the surface of MgO single crystal substrate in chemical mechanical polishing process

Etching and chemical mechanical polishing (CMP) experiments of the MgO single crystal substrate with an artificial scratch on its surface are respectively performed with the developed polishing slurry mainly containing 2 vol.% phosphoric acid (H₃PO₄) and 10-20 nm colloidal silica particles, through observing the variations of the scratch topography on the substrate surface in experiments process, the mechanism and effect of removing scratch during etching and polishing are studied, some evaluating indexes for effect of removing scratch are presented. Finally, chemical mechanical polishing experiments of the MgO substrates after lapped are conducted by using different kinds of polishing pads, and influences of the polishing pad hardness on removal of the scratches on the MgO substrate surface are discussed.     

Evaluation of recipes for obtaining single terminated perovskite oxide substrates

We have re-assessed different methods to obtain single terminated perovskite oxide substrate surfaces of SrTiO₃, LaAlO₃ and NdGaO₃. The surfaces have been probed by a combination of atomic and lateral force microscopy, X-ray photoelectron spectroscopy and reflection high-energy electron diffraction. (0 0 1)SrTiO₃ surfaces were prepared with HF or plasma etching and annealing, (0 0 1)LaAlO₃ surfaces were prepared with or without HCl etching and a consecutive annealing at 750-1100 °C, and (1 1 0)NdGaO₃ surfaces were only annealed. Two of the recipes have previously been suggested to result in A-site terminated surfaces. However, except for the case of high-temperature annealed LaAlO₃ where we observe a double-terminated surface, our data suggest that the single terminated surfaces obtained by these methods were of B-site type.     

The effect of hydrogen as an additive in reactive ion etching of GaAs for obtaining polished surface

The effect of hydrogen on the reactive ion etching (RIE) of GaAs in the CF₂Cl₂ plasma is discussed. The addition of hydrogen into the reaction mixture improves the sharpness of etch borders; the etched surface is smooth for etching depth > 1 μm, etching rate is time-constant.     

Effect of surface preparation on the properties of Au/p-Cd1−xZnxTe

The effect of bromine methanol (BM) etching and NH₄F/H₂O₂ passivation on the Schottky barrier height between Au contact and semi-insulated (SI) p-Cd_1−xZn_xTe (x ≈ 0.09-0.18) was studied through current-voltage (I-V) and capacitance-voltage (C-V) measurements. Near-infrared (NIR) spectroscopy technique was utilized to determine the Zn concentration. X-ray photoelectron spectroscopy (XPS) for surface composition analysis showed that BM etched sample surface left a Te⁰-rich layer, however, which was oxidized to TeO₂ and the surface [Te]/([Cd] + [Zn]) ratio restored near-stoichiometry after NH₄F/H₂O₂ passivation. According to I-V measurement, barrier height was 0.80 ± 0.02-0.85 ± 0.02 eV for Au/p-Cd_1−xZn_xTe with BM etching, however, it increased to 0.89 ± 0.02-0.93 ± 0.02 eV with NH₄F/H₂O₂ passivation. Correspondingly, it was about 1.34 ± 0.02-1.43 ± 0.02 eV and 1.41 ± 0.02-1.51 ± 0.02 eV by C-V method.     

Effects of substrate temperature upon the properties of ZnMgTe layer grown by MOVPE

The effects of substrate temperature upon the optical property, composition and surface morphology have been investigated on nominally undoped Zn_1−xMg_xTe layers grown on (1 0 0) ZnTe substrates by atmospheric pressure metal organic vapor phase epitaxy (MOVPE). It was found that Mg composition increases with decreasing substrate temperature. The result of low temperature photoluminescence (PL) measurement suggests that the optical quality of Zn_1−xMg_xTe layers becomes better with decreasing substrate temperature. On the other hand, there is a narrow range of optimal substrate temperature for a smooth surface morphology. For all the layers, a two-mode behavior with ZnTe- and MgTe-like longitudinal optical phonon modes was confirmed by Raman scattering.     

Reactive ion etching of FePt using inductively coupled plasma

We propose a reactive ion etching (RIE) process of an L1₀-FePt film which is expected as one of the promising materials for the perpendicular magnetic recording media. The etching was carried out using an inductively coupled plasma (ICP) RIE system and an etching gas combination of CH₄/O₂/NH₃ was employed. The L1₀-FePt films were deposited on (1 0 0)-oriented MgO substrates using a magnetron sputtering system. The etching masks of Ti were patterned on the FePt films lithographically. The etch rates of ∼16 and ∼0 nm/min were obtained for the FePt film and the Ti mask, respectively. The atomic force microscopy (AFM) analyses provided the average roughness (R_a) value of 0.95 nm for the etched FePt surface, that is, a very flat etched surface was obtained. Those results show that the highly selective RIE process of L1₀-FePt was successfully realized in the present study.     

The study on the surface state of CdZnTe (1 1 0) surface

Angle-resolved photoemission spectroscopy (ARPES) was used to characterize the surface state of clean CdZnTe (1 1 0) surface. The surface state of CdZnTe with the peak at 0.9 eV below the Fermi level is identified. Meanwhile, Photoluminescence (PL) spectrum confirmed that there existed a surface trap state which introduced a deep-level peak at 1.510 eV. The surface trap states can be decreased by aging in dry-air. The surface leakage current was measured also by I-V measurements. After aging, the leakage current was decreased remarkably, which suggested that the aging treatment is an effective method to decrease the surface trap state.     

Enhanced in vitro biocompatibility of ultrafine-grained biomedical NiTi alloy with microporous surface

Bulk ultrafine-grained Ni_50.8Ti_49.2 alloy (UFG-NiTi) was successfully fabricated by equal-channel angular pressing (ECAP) technique in the present study, and to further improve its surface biocompatibility, surface modification techniques including sandblasting, acid etching and alkali treatment were employed to produce either irregularly roughened surface or microporous surface or hierarchical porous surface with bioactivity. The effect of the above surface treatments on the surface roughness, wettability, corrosion behavior, ion release, apatite forming ability and cytocompatibility of UFG-NiTi alloy were systematically investigated with the coarse-grained NiTi alloy as control. The pitting corrosion potential (E_pit) was increased from 393 mV (SCE) to 704 mV (SCE) with sandblasting and further increased to 1539 mV (SCE) with following acid etching in HF/HNO₃ solution. All the above surface treatment increased the apatite forming ability of UFG-NiTi in varying degrees when soaked them in simulated body fluid (SBF). Meanwhile, both sandblasting and acid etching could promote the cytocompatibility for osteoblasts: sandblasting enhanced cell attachment and acid etching increased cell proliferation. The different corrosion behavior, apatite forming ability and cellular response of UFG-NiTi after different surface modifications are attributed to the topography and wettability of the resulting surface oxide layer.     

Atomic force microscopy investigation of surface roughness generated between SiO2 micro-pits in CHF3/Ar plasma

The present paper investigates the surface roughness generated by reactive ion etching (RIE) on the location between silicon dioxide (SiO₂) micro-pits structures. The micro-pit pattern on polymethyl methacrylate (PMMA) mask was created by an electron beam lithography tool. By using PMMA as a polymer resist mask layer for pattern transfer in RIE process, the carbon (C) content in etching process is increased, which leads to decrease of F/C ratio and causes domination of polymerization reactions. This leads to high surface roughness via self-organized nanostructure features generated on SiO₂ surface which was analyzed using atomic force microscopy (AFM) technique. The etching chemistry of CHF₃ plasma on PMMA masking layer and SiO₂ is analyzed to explain the polymerization. The surface root-mean-square (RMS) roughness below 1 nm was achieved by decreasing the RF power to 150 W and process pressure lower than 10 mTorr.     

Metal-CdZnTe contact and its annealing behaviors

The electrical properties of different metal-CdZnTe contacts by sputtering deposition method are investigated by current-voltage. The results show that Au is the most suitable electrical contact materials, which forms the nearly ideal Ohmic contact with high resistivity p-CdZnTe crystals. Ohmicity coefficient b is the closest to 1 after 10 min annealing at 333 K, which is analyzed by current-voltage characteristics. XPS analyses show that Au atoms diffuse into CdZnTe during annealing process and Cd and Te atoms diffuse into Au contact. Diffused Au atoms do not form any compound with any element in CdZnTe crystal. PL spectra results of Au deposition on CdZnTe crystals at 10 K show that the inter-diffused donors [Au]³⁺ recombine with acceptors [V_Cd]²⁻ during sputtering process. Meanwhile, the intensity of (D_complex) peak of with Au contact increases sharply in comparison with un-deposited CdZnTe crystal and donor [Au]³⁺ and can compensate Cd vacancy [V_Cd]²⁻ wholly.     

Dry etching of CuCrO2 thin films

Highly conducting films of p-type CuCrO₂ are attractive as hole-injectors in oxide-based light emitters. In this paper, we report on the development of dry etch patterning of CuCrO₂ thin films. The only plasma chemistry that provided some chemical enhancement was Cl₂/Ar under inductively coupled plasma conditions. Etch rates of ∼500 Å min⁻¹ were obtained at chuck voltages around −300 V and moderate source powers. In all cases, the etched surface morphologies were improved relative to un-etched control samples due to the smoothing effect of the physical component of the etching. The threshold ion energy for the onset of etching was determined to be 34 eV. Very low concentrations (≤1 at.%) of residual chlorine were detected on the etched surfaces but could be removed by simple water rinsing.     

Chemical etching investigation of polycrystalline p-type 6H-SiC in HF/Na2O2 solutions

In this work, an experimental study on the chemical etching reaction of polycrystalline p-type 6H-SiC was carried out in HF/Na₂O₂ solutions. The morphology of the etched surface was examined with varying Na₂O₂ concentration, etching time, agitation speed and temperature. The surfaces of the etched samples were analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) Fourier transform infrared spectroscopy (FT-IR) and photoluminescence. The surface morphology of samples etched in HF/Na₂O₂ is shown to depend on the solution composition and bath temperature. The investigation of the HF/Na₂O₂ solutions on 6H-SiC surface shows that as Na₂O₂ concentration increases, the etch rate increases to reach a maximum value at about 0.5 M and then decreases. A similar behaviour has been observed when temperature of the solution is increased. The maximum etch rate is found for 80 °C. In addition, a new polishing etching solution of 6H-SiC has been developed. This result is very interesting since to date no chemical polishing solution has been developed on the material.     

STM study of acetylene reaction with Si(1 1 1): observation of a carbon-induced Si(1 1 1)√3×√3R30° reconstruction

The first stages of acetylene reaction with the Si(1 1 1)7 × 7 reconstructed surface kept at 600 °C are studied by recording scanning tunneling microscopy (STM) images during substrate exposure at a C₂H₂ pressure of 2 × 10⁻⁴ Pa (2 × 10⁻² mbar). We observed the progressive substitution of the 7 × 7 reconstruction with a carbon induced Si(1 1 1)√3×√3R30° reconstruction characterized by an atomic distance of 0.75 ± 0.02 nm, very close to that of the silicon 7 × 7 adatoms. This means that a carbon enrichment of the silicon outermost layers occurs giving rise to the formation of a Si-C phase different from the √3×√3R30° reconstruction typical of Si terminated hexagonal SiC(0 0 0 1) surface with an atomic distance of 0.53 nm. To explain STM images, we propose a reconstruction model which involves carbon atoms in T₄ and/or S₅ sites, as occurring for B doped Si(1 1 1) surface. Step edges and areas around the silicon surface defects are the first regions involved in the reaction process, which spreads from the upper part of the step edges throughout the terraces. Step edges therefore, progressively flakes and this mechanism leads, for the highest exposures, to the formation of large inlets which makes completely irregular the straight edge typical of the Si(1 1 1)7 × 7 terraces. These observations indicate that there occurs an atomic diffusion like that driving the meandering effect. Finally, the formation of a few crystallites is shown also at the lowest acetylene exposures. This is the first STM experiment showing the possibility to have carbon incorporation in a Si(1 1 1) matrix for higher amounts than expected, at least up to 1/6 of silicon atomic layer.     

Temperature-dependent modifications in the surface composition of Finemet: A ToF-SIMS study

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was employed as an in situ tool to study the temperature-induced alteration of the surface composition of amorphous Finemet, Fe₇₃Si_15.8B_7.2Cu₁Nb₃. Temperature was changed reversibly by cooling from room temperature to 118 K and warming back to room temperature. As a general result, the ion intensities and, consequently, the surface concentrations of the alloy constituents were found to vary non-monotonously. Therefore segregation processes were in operation the extent of which was element-specific. Most importantly, while cycling the temperature hysteresis behaviour was observed with concentration of Fe developing just opposite to that of the alloying elements. Accordingly, on cooling the alloy, the surface enrichment with B, Si, Nb, Cu attained first a maximum in the range of 248-193 K before the segregation changed the trend to establish appreciable depletion of these elements at 118 K (as compared to room temperature). By contrast, the surface iron content developed inversely and decreased first to a minimum at ∼223 K before reaching enrichment at 118 K. During warming, a maximum segregation of boron and silicon was observed at about 223 K - similar as on cooling - so that this temperature can be considered characteristic of the segregation process. Dissociative adsorption of water from the residual atmosphere occurring at low temperatures was responsible for the formation of surface hydroxides of iron, silicon and niobium; an enhanced adsorption of molecular water was observed at temperatures below 153 K. The temperature-dependent segregation and adsorption-desorption processes were found to be largely reversible, so that the surface composition of Finemet was practically restored after finishing the cooling-warming cycle. The processes and factors governing the non-monotonous temperature dependence of the surface segregation in the amorphous alloy are discussed within the frame of segregation theory and the influence of temperature-induced tensile stress on segregation.     

CF interaction with Si(1 0 0)-(2 × 1): Molecular dynamics simulation

In this study, the interaction of CF with the clean Si(1 0 0)-(2 × 1) surface at normal incidence and room temperature was investigated using molecular dynamics simulation. Incident energies of 2, 12 and 50 eV were simulated. C atoms, arising from dissociation, preferentially react with Si to form Si-C bonds. A Si_xC_yF_z interfacial layer is formed, but no etching is observed. The interfacial layer thickness increases with increasing incident energy, mainly through enhanced penetration of the silicon lattice. Silicon carbide and fluorosilyl species are formed at 50 eV, which is in good agreement with available experimental data. The level of agreement between the simulated and experimental results is discussed.     

Biological functionalization and patterning of porous silicon prepared by Pt-assisted chemical etching

Porous silicon fabricated via Pt-assisted chemical etching of p-type Si (1 0 0) in 1:1:1 EtOH/HF/H₂O₂ solution possesses a longer durability in air and in aqueous media than anodized one, which is advantageous for biomedical applications. Its surface SiHx (x = 1 and 2) species can react with 10-undecylenic acid completely under microwave irradiation, and subsequent derivatizations of the end carboxylic acid result in affinity capture of proteins. We applied two approaches to produce protein microarrays: photolithography and spotting. The former provides a homogeneous microarray with a very low fluorescence background, while the latter presents an inhomogeneous microarray with a high noise background.     

Investigation of etch characteristics of non-polar GaN by wet chemical etching

We characterized the surface defects in a-plane GaN, grown onto r-plane sapphire using a defect-selective etching (DSE) method. The surface morphology of etching pits in a-plane GaN was investigated by using different combination ratios of H₃PO₄ and H₂SO₄ etching media. Different local etching rates between smooth and defect-related surfaces caused variation of the etch pits made by a 1:3 ratio of H₃PO₄/H₂SO₄ etching solution. Analysis results of surface morphology and composition after etching by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) demonstrated that wet chemical etching conditions could show the differences in surface morphology and chemical bonding on the a-plane GaN surface. The etch pits density (EPD) was determined as 3.1 × 10⁸ cm⁻² by atom force microscopy (AFM).     

Influence of surface preparation on CdZnTe nuclear radiation detectors

High resolution X-ray diffraction (HRXRD), Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM) techniques were used to characterize the surface of CdZnTe (CZT) samples treated by mechanical lapping, polishing and chemical etching processes. The results confirm that the etching process produces the highest intensity diffraction peak, and the best full-width-at-half-maximum (FWHM). Fourier Transform Infrared (FTIR) spectroscopy shows that fine polishing increases the infrared transmission of the CZT sample, while etching with 2% bromine methanol (BM) etching decreases the infrared transmission. Different etchants and concentrations were investigated by comparing the surface morphology and roughness. The bromine methanol etching has shown more flat surface with lower roughness than the other etchants.     

Effects of in situ thermal annealing on the structural, optical, and electrical properties in Hg0.7Cd0.3Te epilayers grown on CdTe buffer layers

Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) transmission, and Hall effect measurements were performed to investigate the structural, optical, and electrical properties of as-grown and in situ-annealed Hg_0.7Cd_0.3Te epilayers grown on CdTe buffer layers by using molecular beam epitaxy. After the Hg_0.7Cd_0.3Te epilayers had been annealed in a Hg-cell flux atmosphere, the SEM images showed that the surface morphologies of the Hg_0.7Cd_0.3Te thin films were mirror-like with no indication of pinholes or defects, and the FTIR spectra showed that the transmission intensities had increased in comparison to that of the as-grown Hg_0.7Cd_0.3Te epilayer. Hall-effect measurements showed that n-Hg_0.7Cd_0.3Te epilayers were converted to p-Hg_0.7Cd_0.3Te epilayers. These results indicate that the surface, optical, and electrical properties of the Hg_1 − xCd_xTe epilayers are improved by annealing and that as-grown n-Hg_1 − xCd_xTe epilayers can be converted to p-Hg_1 − xCd_xTe epilayers by in situ annealing.