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SEM images of a-SiC samples after anodization in the 1% HF electrolyte with and without Triton X-100. Our further investigations showed that without Triton X-100 surfactant in the electrolyte, the anodic etching process could also occur, provided that the etchant is HF-dilute enough. Additionally, for the case of the electrolyte without surfactant, the anodizing voltage applied to the sample must be higher than for the case of the electrolyte with surfactant. For example, for the 1% HF etchant without Triton X-100, if the anodizing voltage was 250 V sharing between the sample and a 14 kΩ resistor, there was no etching, but if we used 300 V sharing between the sample and a 3.4 kΩ resistor, we could
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Porous amorphous SiC (a-SiC) layer with pore size in the nanometer region was fabricated on the a-SiC/Si substrates by the electrochemical etching method using HF/H2O/surfactant solution. Systematic study showed that the HF concentration in the etching solution (in the 1–73% region) strongly affects the structure (both the pore size and the pore de...
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... a good etching process. The results of this experiment are shown in figure 3. It is worth noting that although the anodic etching process could take place in the electrolyte without surfactant, the morphology of the obtained porous a-SiC layer is totally different in comparison with the case of the electrolyte with 1% Triton X-100. ...
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... Porous SiC was first fabricated by Shor et al. [8] by using anodic etching method, which anodizing single crystal n-type 6H-SiC in hydrofluoric acid and under UV illumination. Since then, a lot of studies of porous SiC have been reported with specific changes in morphology, optical transmittance and photoluminescence (PL) properties after the formation of porous structures in both 6H and 4H n-type or p-type SiC wafers [4,5,[9][10][11][12][13][14][15]. ...
Porous 6H-SiC samples with different thicknesses were fabricated through anodic etching in diluted hydrofluoric acid. Scanning electron microscope images show that the dendritic pore formation in 6H-SiC is anisotropic, which has different lateral and vertical formation rates. Strong photoluminescence was observed and the etching process was optimized in terms of etching time and thickness. Enormous enhancement as well as redshift and broadening of photoluminescence spectra were observed after the passivation by atomic layer deposited Al2O3 and TiO2 films. No obvious luminescence was observed above the 6H-SiC crystal band gap, which suggests that the strong photoluminescence is ascribed to surface state produced during the anodic etching.
... Furthermore, most studies have fabricated porous SiC using bulk crystalline SiC, while few studies have fabricated porous SiC from thin films. 2,3,[7][8][9][10][11][12][13][14] SiC thin films are easy to make and relatively inexpensive compared with bulk SiC, and we believe that thin films are suitable for most applications. In many applications, the SiC thin film may be amorphous rather than crystalline: for example, researchers have reported using amorphous SiC thin films to fabricate humidity sensors 2 and ammonia sensors. ...
... To ensure that only the aSiC surface was exposed to the electrolyte during anodic etching, the backside and edges of the samples were protected with a polystyrene layer, as done in our previous report. 14 The four edges of the square aSiC samples were covered by 2-mm-wide strips of polystyrene, leaving 1 × 1 cm 2 exposed to the etching solution. With this arrangement, we observed no edge (fringing) effects. ...
In this report, we fabricated a porous layer in amorphous SiC thin films by using
constant-current anodic etching in an electrolyte of aqueous diluted hydrofluoric acid.
The morphology of the porous amorphous SiC layer changed as the anodic current
density changed: At low current density, the porous layer had a low pore density
and consisted of small pores that branched downward. At moderate current density,
the pore size and depth increased, and the pores grew perpendicular to the surface,
creating a columnar pore structure. At high current density, the porous structure
remained perpendicular, the pore size increased, and the pore depth decreased. We
explained the changes in pore size and depth at high current density by the growth
of a silicon oxide layer during etching at the tips of the pores.
... Furthermore, most studies have fabricated porous SiC using bulk crystalline SiC, while few studies have fabricated porous SiC from thin films. 2,3,[7][8][9][10][11][12][13][14] SiC thin films are easy to make and relatively inexpensive compared with bulk SiC, and we believe that thin films are suitable for most applications. In many applications, the SiC thin film may be amorphous rather than crystalline: for example, researchers have reported using amorphous SiC thin films to fabricate humidity sensors 2 and ammonia sensors. ...
... To ensure that only the aSiC surface was exposed to the electrolyte during anodic etching, the backside and edges of the samples were protected with a polystyrene layer, as done in our previous report. 14 The four edges of the square aSiC samples were covered by 2-mm-wide strips of polystyrene, leaving 1 × 1 cm 2 exposed to the etching solution. With this arrangement, we observed no edge (fringing) effects. ...
In this report, we fabricated a porous layer in amorphous SiC thin films by using constant-current anodic etching in an electrolyte of aqueous diluted hydrofluoric acid. The morphology of the porous amorphous SiC layer changed as the anodic current density changed: At low current density, the porous layer had a low pore density and consisted of small pores that branched downward. At moderate current density, the pore size and depth increased, and the pores grew perpendicular to the surface, creating a columnar pore structure. At high current density, the porous structure remained perpendicular, the pore size increased, and the pore depth decreased. We explained the changes in pore size and depth at high current density by the growth of a silicon oxide layer during etching at the tips of the pores.
... Nevertheless, some authors report the addition of other agents such as Triton X-100 for example. 16 In this study, we demonstrate that the use of various surfactants (Triton X-100, Cetyltrimethylammonium chloride or Ammonium dodecylsulfate) or solvants (acetic acid) can lead to significant differences between porous layers when a constant anodization current is applied. ...
... 19 This surfactant was also used by Cao and coworkers to etch amorphous SiC. 16 If we observe a sample etched in an electrolyte where 120 ppm of Triton X-100 is added (Figure 2), we can notice a drastic change of morphology in depth. Indeed, a low porosity stratified structure (Figure 2a) is replaced by chevron-like pores ( Figure 2b) and finally, in the bottom of the layer, by very highly branched pores (Figure 2c). ...
... 28,29 In the case of SiC, Cao and coworkers have studied HF concentration effects but only in the case of amorphous SiC anodization. 16 They reported also a drastic reduction of the pore size when increasing the HF concentration. Moreover, the samples studied in 16 were observed only on the surface using top view images. ...
In this paper, we study the electrochemical anodization of n-type heavily doped 4H-SiC wafers in HF based electrolytes without any UV light assistance. We present, in particular, the differences observed when varying the process conditions such as the HF concentration, the type of additive and the applied current regime. The use of a solvent such as acetic acid seems to be more suitable to produce homogeneous morphologies compared with Cetyltrimethylammonium chloride (CTAC), Ammonium dodecylsulfate (ADS), Triton X-100 surfactants. In addition, the use of pulsed current regimes improves the global homogeneity of the porous layers. Nevertheless, for some unexplained reasons, at specific concentrations of 15 and 50%, this homogeneity cannot be ensured and the observed morphology mixes mesopores and macropores with random orientations.
... Most of the time, the ethanol is used to increase the electrolyte wettability. However, some authors report the addition of other agents such as Triton X-100 for example [9]. Nevertheless, acetic acid has proven its efficiency in the case of porous silicon etching [10]. ...
... Most of the time, the ethanol is used to increase the electrolyte wettability. However, some authors report the addition of other agents such as Triton X-100 for example [9] . Nevertheless , acetic acid has proven its efficiency in the case of porous silicon etching [10]. ...
In this paper, we study the electrochemical anodization of n-type heavily doped 4 H-SiC wafers in a HF-based electrolyte without any UV light assistance. We present, in particular, the differences observed between the etching of Si and C faces. In the case of the Si face, the resulting material is mesoporous (diameters in the range of 5 to 50 nm) with an increase of the `chevron shaped¿ pore density with depth. In the case of the C face, a columnar morphology is observed, and the etch rate is twice greater than for the one for the Si face. We've also observed the evolution of the potential for a fixed applied current density. Finally, some wafer defects induced by polishing are clearly revealed at the sample surfaces even for very short etching times.
Third-generation semiconductors have richer and better properties than traditional semiconductors, and show promising application prospects in high-power, high-temperature, high-frequency, and optoelectronic devices. Therefore, they have gained increasing interest and received extensive research attention in recent years. Electrochemical etching plays an important role in exploring the properties of third-generation semiconductors and related device fabrication. This paper systematically reviews the electrochemical etching process of silicon carbide and gallium nitride which are the typical representative of the third-generation semiconductors. Through subdividing the electrochemical etching approach into anodic oxidation etching, photoelectrochemical etching, and electroless photoelectrochemical etching, the mechanism of each electrochemical etching method is expounded, the influences of various etching parameters on the etching results are discussed, and the related applications of electrochemical etching in characterizing crystal defects, processing micro-nano structures, and fabricating microelectronic devices are summarized. Finally, future development in achieving more efficient electrochemical etching is briefly discussed. In general, this paper provides a systematic review of the electrochemical etching of third-generation semiconductors, which is helpful for researchers to supplement the content in this field, and even non-researchers in this field will be able to familiarize themselves with the relevant content quickly.
Silicon carbide (SiC) is one of the most important third‐generation semiconductor materials. However, the chemical robustness of SiC makes it very difficult to process, and only very limited methods are available to fabricate nanostructures on SiC. In this work, a hybrid anodic and metal‐assisted chemical etching (MACE) method is proposed to fabricate SiC nanowires based on wet etching approaches at room temperature and under atmospheric pressure. Through investigations of the etching mechanism and optimal etching conditions, it is found that the metal component plays at least two key roles in the process, i.e., acting as a catalyst to produce hole carriers and introducing band bending in SiC to accumulate sufficient holes for etching. Through the combined anodic and MACE process the required electrical bias is greatly lowered (3.5 V for etching SiC and 7.5 V for creating SiC nanowires) while enhancing the etching efficiency. Furthermore, it is demonstrated that by tuning the etching electrical bias and time, various nanostructures can be obtained and the diameters of the obtained pores and nanowires can range from tens to hundreds of nanometers. This facile method may provide a feasible and economical way to fabricate SiC nanowires and nanostructures for broad applications.
Carbide-derived carbons (CDCs) are a growing class of nanostructured carbon materials with properties that are desirable for many applications, ranging from electrical energy to gas storage. However, the synthesis of CDCs often requires high temperatures and/or pressures, as well as toxic chemicals. In this report, we demonstrate environmentally friendly synthesis of a carbon-rich layer on the surface of SiC by anodic etching at room temperature in a highly diluted solution of hydrofluoric acid in ethylene glycol. In our opinion, the carbon-rich layer was formed thanks to the fact that we have used the etching conditions in which the rate of removal of carbon from SiC has become significantly lower compared with the silicon removal rate. More specifically, we have created an environment for SiC anodic etching where there is little water. In such conditions, silicon is still being removed from SiC, thanks to the direct dissolution, whereas the carbon removal rate is significantly reduced, due to the fact that carbon can be lost only by oxidation, but there is not enough water to oxidize carbon as in solutions with plenty of water. Thus, a carbon-rich layer is created on the etched SiC surface.
In this study, we show I-V characterizations of various metal/porous silicon carbide (pSiC)/silicon
carbide (SiC) structures. SiC wafers were electrochemically etched from the Si and C faces in the
dark or under UV lighting leading to different pSiC morphologies. In the case of low porosity pSiC
etched in the dark, the I-V characteristics were found to be almost linear and the extracted resistivities
of pSiC were around 1.5 � 104 X cm at 30 �C for the Si face. This is around 6 orders of magnitude
higher than the resistivity of doped SiC wafers. In the range of 20-200 �C, the activation
energy was around 50 meV. pSiC obtained from the C face was less porous and the measured average
resistivity was 10 X cm. In the case high porosity pSiC etched under UV illumination, the resistivity
was found to be much higher, around 1014 X cm at room temperature. In this case, the
extracted activation energy was estimated to be 290 meV.
We achieved surface polishing on n-type 3C-polycrystalline SiC by means of electrochemical etching in diluted hydrofluoric acid (HF) solutions under constant applied current density, without the need of UV illumination. Electropolishing provides a smooth surface and reduction of roughness values by more than one half compared to the initial value. The polished surface is flat and featureless, with no sign of intergranular corrosion or other degradation phenomena related to the polycrystalline structure. Etching conditions such as HF concentration, current density, and etching time were varied in order to assess optimized values for polishing.
