Photoelectrochemical Etching Method Research Articles

Influence Study of Etching Time for Porous Silicon on Morphological, Optical, Electrical and Spectral Responsivity Properties

In this investigation, n-type (100) silicon wafers with a thickness of 600 ± 25 μm and resistance of 0.1-100 μΩ were used to manufacture porous silicon. With the aid of hydrofluoric acid (HF) with a 20% concentration, a current density of 20 mA/cm2, and various experimental drilling times of 5, 15, and 25 minutes with the fixation of other parameters, the photoelectrochemical etching method was successful. The morphology of porous silicon was investigated using scanning electron microscopy (SEM), the XRD- diffraction wide of porous silicon creation with rising apex peaks was confirmed, and (AFM) sponge-like morphology was seen, and the pore diameter grew larger as drilling time rose. In a drilling time of 15 minutes, it is able to quantify both the vibrational and electrical characteristics of the energy band gap using Raman analysis and PL detection. Investigate sample samples' current voltage readings (J-V) at various etching times. Additionally, we discovered devices with a broad wavelength that react to the response in the investigation of the spectrum response PS AL/PS/SI/Al as a photodetector.

The Structural and Optical Investigation of Grown GaN Film on Porous Silicon Substrate Prepared by PLD

The optical properties of a grown gallium nitride (GaN) thin film on a porous silicon (P-Si) substrate was investigated. A Photo-electrochemical etching method was used to synthesize the Psi substrate, and a physical deposition method (pulsed laser deposition) of 1064 nm Q-switch Nd: YAG laser with a vacuum of 10−2 mbar was used to grow a thin layer of GaN on a prepared P-Si substrate. X-Ray diffraction displayed that GaN film has a high crystalline nature at the (002) plane. The photoluminescence of GaN film exhibited ultraviolet PL with a peak wavelength of 374 nm corresponding to GaN material and red PL with a peak wavelength of 730 nm corresponding to Psi substrate. The absorption coefficient of the P-Si substrate and grown GaN thin film was obtained from the absorption calculation of UV-Vis diffused spectroscopy at ambient temperature in the 230–1100 nm wavelength range. Extinction coefficients, optical energy gap, and refractive index of both the P-Si substrate and the grown GaN thin film have been determined, respectively. The direct optical energy gaps of both the P-Si substrate and grown GaN have also been determined using three methods: Plank’s relation with photoluminescence (PL) spectroscopy, Tauc'relation, and Kubulka-Munk argument with Uv-Vis diffused spectroscopy. It was observed that the optical energy gap of the P-Si substrate was 2.1 eV, while the grown GaN thin film had a multi-optical energy gap of 3.3 eV and 1.6 eV. A good agreement has been obtained between these mentioned methods.

Fabrication of UV photodetector based on GaN/ Psi heterojunction using pulse laser deposition method: Effect of different laser wavelengths

In this study, GaN/pSi heterojunction photodetectors were fabricated via pulsed laser deposition method (PLD). Photoelectrochemical etching method (PECE) with laser aid prepared a pSi substrate. Different laser wavelengths were tested on GaN and pSi films' structural, spectroscopic, electrical, and performance characteristics. XRD showed that GaN/pSi heterojunction photodetectors were polycrystalline and hexagonal. PL measurements showed two emission peaks attributable to GaN films (374, 364, 359 nm) and the pSi substrate (730, 729, 729 nm). Shorter laser wavelengths raised the GaN/pSi heterojunction's optical energy gap from 3.271 to 3.3415 eV. FESEM pictures showed that the average size of the manufactured samples was 51.88, 36.12, and 22.76 nm for spherical nanoparticles and a cauliflower-like shape. Atomic force microscopy (AFM) results show the root mean square of the surface roughness of prepared samples to be 4.83, 8.87, and 14.51 nm, respectively, as the laser wavelength became shorter with full coverage of all pores of prepared pSi. GaN/pSi heterojunction photodetectors had rectification in their dark I–V characteristics, and the heterojunction made at 355 nm had the best junction characteristics. The spectral responsivity of GaN/pSi photodetectors shows that the maximum responsivity was 29.01 A/W at 370 nm for a photodetector prepared at 355 nm. High detectivity and external quantum efficiency were 8.02×10+12 Jones and 359.73% at 370 nm, respectively. The photodetector fabricated using 355 nm showed a fast rise time of 328μsec and a fall time of 617μsec.

Effect of Different Etching Time on Fabrication of an Optoelectronic Device Based on GaN/Psi

Gallium nitride (GaN)/porous silicon (PSi) film was prepared using a pulsed laser deposition method and 1064 nm Nd: YAG laser for optoelectronic applications and a series of Psi substrates were fabricated using a photoelectrochemical etching method assisted by laser at different etching times for 2.5–15 min at 2.5 min intervals. X-ray diffraction, room-temperature photoluminescence, atomic force microscopy and field emission scanning electron microscopy images, and electrical characteristics in the prepared GaN on the Psi film were investigated. The optimum Psi substrate was obtained under the following conditions: 10 min, 10 mA/cm2, and 24% hydrofluoric acid. The substrate exhibited two highly cubic crystalline structures at (200) and (400) orientations and yellow visible band photoluminescence, and homogeneous pores formed over the entire surface. The pores had steep oval shapes and were accompanied by small dark pores that appeared topographically and morphologically. The GaN/Psi film fabricated through PLD exhibited a high and hexagonal crystallographic texture in the (002) plane. Spectroscopic properties results revealed that the photoluminescence emission of the deposited nano-GaN films was in the ultraviolet band (374 nm) related to GaN material and in the near-infrared band (730 nm) related to the Psi substrate. The topographical and morphological results of the GaN films confirmed that the deposited film contained spherical grains with an average diameter of 51.8 nm and surface roughness of 4.8 nm. The GaN/Psi surface showed a cauliflower-like morphology, and the built-in voltage decreased from 3.4 to 2.7 eV after deposition. The fabricated GaN/Psi film exhibited good electrical characteristics.

Effect of etching current density on spectroscopic, structural and electrical properties of porous silicon photodetector

In this work, we compare the results obtained when with different etching current densities (6, 13, 20, 27, and 34) mA/cm2 on Structural, morphological; Raman, and photoluminescence spectra, Electrical, photodetector of Porous Silicon (PS), and have been studied. A diode laser with a wavelength of 532 nm and a power of 200 mW was utilized to irradiate silicon n-type immersed in HF to the formation of PS by Photoelectrochemical etching method with resistivity (0.1–100 ohm.cm) in hydrofluoric ratio 16% (HF: ethanol) for 10 min. XRD results for the PS increasing etching current the decreasing crystallites size while morphological characteristics average diameter increased and pores have been seen cylindrical forms. Raman small shifts of in the left appear between (514–493) cm-1 and decrease in the crystal size because of the quantum confinement. The energy bandgap (Eg) increases from 1.89 eV to 1.93 eV when current densities increase. (J-V) and (Jph-V) characteristics in both dark and photocurrent density output current reduces as the current density of etching rises and the reduction in photocurrent. Detectivity is a consequence of resonant frequencies, and maximum quantum efficiency of 52% was reached at 800 nm in current density etching at 20 mA/cm2.

Synthesis and characterization of carbon nanotube doped with zinc oxide nanoparticles CNTs-ZnO/PS as ethanol gas sensor

Nanocomposites have the potential to produce very selective, stable, and sensitive sensors. Nanocomposites porous structures have a larger surface area for gas molecule adsorption. In this paper, the high quality gas sensor was prepared by modified porous layer of silicon (PS) with a thin layer of carbon nanotube (CNTs) and carbon nanotube doped with zinc oxide (ZnO) nanoparticles (70–30)% respectively. PS samples were created using the photoelectrochemical etching method (PECE), for N-type silicon (Si) wafer with resistivity of (1.5–4) Ω cm and a thickness (580 ± 0.25) μm. Three etching current densities were employed for prepare PS layers 12, 24, and 30 mA/cm2, while, the hydrofluoric acid HFc concentration of 40% and etching time was about 10 min. The Structure characteristics, morphological features, and surface chemical bond formation of all PS and (MWCNTs-ZnO/PS) samples were examined using X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), and Transition Electron Microscope (TEM). All PS and MWCNTs-ZnO/PS samples were applied as ethanol gas sensors at room temperature. The results revealed that CNTs-ZnO/PS had the highest sensitivity to ethanol gas at etching current density 30 mA/cm2, reaching about (2.004984) at a concentration of 500 ppm. Fusion of CNTs-ZnO leads to the emergence of new properties and unique effects, and as a result of the excellent sensing ability of carbon nanotubes in detecting different gases at room temperature, Used in the manufacture of highly selective gas sensors that operate at room temperature. The Interest of this article return to study the effect of extremely high surface to volume ratio (increasing surface area), and ease composition and compatibility with modern silicon microelectronics manufacturing technologies.

Non-polar GaN/AlGaN quantum-well polariton laser at room temperature

We demonstrate room temperature (RT) polariton lasing in an all-dielectric microcavity containing non-polar III-nitride quantum wells (QWs) as active media. The microcavity is fabricated using the photo-electrochemical etching method, by which an optimally grown $m$-plane III-nitride active region is detached from the substrate in the form of a membrane, which is subsequently inserted between two $\mathrm{Si}{\mathrm{O}}_{2}/{\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$ distributed Bragg reflectors, with 4 and 10 pairs for the top and bottom mirrors, respectively. The active region consists of 25 $\mathrm{GaN}/{\mathrm{Al}}_{0.1}{\mathrm{Ga}}_{0.9}\mathrm{N}$ (5 nm/3 nm) QWs. The produced microcavities exhibit two closely spaced polarization-resolved lower polariton branches at RT, in line with the selection rules of the non-polar orientation, having a Rabi splitting of 62 and 72 meV in the $E\ensuremath{\parallel}a$ and $E\ensuremath{\parallel}c$ polarizations, respectively. In a positively detuned 3\ensuremath{\lambda}/2-thick microcavity, polariton lasing is observed at ambient conditions in the $E\ensuremath{\parallel}a$ polarization, with a threshold \ensuremath{\sim} 3 times lower than previous state of the art, despite the use of a relatively weak top reflector.

Characterization of Silver Nanoparticles on Porous silicon by Laser ablation in Liquid

In this article, Porous silicon was prepared using a photo-electrochemical etching method of n-type silicon at etching times (5 and 15 min.). The silver nanoparticles were coated on porous silicon by laser ablation in liquid with energy 400, 600, and 800 mJ. Atomic force microscope images showed an increase of pores size with etching time and it becomes smaller in diameter after laser ablation. Moreover, Scanning electron microscope displayed an aggregates formation when increasing laser energy. The strong peak of absorption of AgNPs found around 415-420 nm. The absorption amplitude increased when laser energy increases. Therefore, the nanostructures on the porous silicon properties play a crucial role in the formation of the homogeneity and this improves the structural stability of PSi layer.

Photo-Electrochemical Etching of Single Crystalline β-Ga2O3 Thin Film

β-Ga2O3 is a next-generation semiconductor material having ultra-wide bandgap energy of 4.8 eV and excellent electrical properties. So it is expected to be suitable for various applications such as power electronics, solar-blind UV photodetectors and gas sensors. However, there are some issues to overcome in order for β-Ga2O3 to be commercialized. Among them, crystal defects are important factor that significantly affects device performance. Defects are formed intrinsically during the growth process, or caused by high-energy plasma ion during dry etching. It has been reported that the electrical characteristics are deteriorated in the device such as MOSFET and MISFET fabricated by inductively coupled plasma etching. Unlike dry etching, which can cause damage by plasma ions, wet etching is a damage-free process that uses a chemical reaction between the target material and etchant. In addition, wet etching may be used for removing defects by using the etching characteristic, which the chemically unstable defect areas are preferentially etched. However, β-Ga2O3 hardly reacts with etchant at room temperature, and has been reported to have etch rate of several tens of nm/min when acid etchant are used at higher than 100 °C.In our study, we have tried to increase the etch rate of β-Ga2O3 and remove defects effectively by Photo-electrochemical (PEC) etching. PEC etching is a method that promotes the reaction by irradiated light having energy above bandgap and applied external bias. Single crystalline β-Ga2O3 thin films are cleaved in the [100] direction with mechanical force from single crystalline β-Ga2O3 substrate. Ti/Au was deposited to form Ohmic contact with β-Ga2O3 thin films. With the PEC etching method, we could etch at a lower temperature than conventional wet etching. In addition, it was confirmed that the etch rate can be controlled according to the external bias condition. The details of our experiment conditions and results will be presented at the meeting.

Fin-Gated Nanochannel Array Gate-Recessed AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistors

In this article, fin-gated nanochannel array gate-recessed AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOSHEMTs) were fabricated, in which the gate oxide layer was directly grown using the photoelectrochemical (PEC) oxidation method, the gate-recessed structure was formed using the PEC etching method, and the nanochannel array was patterned using the electron-beam lithography system. The improved gate controllability was obtained in devices with a narrower channel width due to the lateral field effect in comparison with those of the conventional planar AlGaN/GaN MOSHEMTs. A threshold voltage of −0.30, −0.35, and −2.3 V, and a subthreshold swing of 95, 109, and 372 mV/dec, were respectively obtained for the AlGaN/GaN MOSHEMTs with a channel width of 80 and 100 nm, and with a planar channel. Furthermore, the associated extrinsic transconductance of 269, 253, and 93 mS/mm was obtained to verify the improved performance of AlGaN/GaN MOSHEMTs using a narrower channel array. Besides, the low-noise and high-frequency performances were also enhanced using a narrower channel width in the fin-gated nanochannel array gate-recessed AlGaN/GaN MOSHEMTs.

Multiple-Submicron Channel Array Gate-Recessed AlGaN/GaN Fin-MOSHEMTs

In this paper, the multiple-submicron channel array gate-recessed AlGaN/GaN fin-metal-oxide-semiconductor high-electron mobility transistors (fin-MOSHEMTs) were fabricated using the photoelectrochemical oxidation method, the photoelectrochemical etching method, and the He-Cd laser interference photolithography method. The multiple-submicron channel array was formed using the He-Cd laser interference photolithography system. The gate-recessed structure and the directly grown gate oxide layer were performed using the photoelectrochemical etching method and the photoelectrochemical oxidation method, respectively. The subthreshold swing and the extrinsic transconductance were improved in the resulting devices with a narrower channel width. Furthermore, the unit gain cutoff frequency and the maximum oscillation frequency were also enhanced using a narrower channel width in the multiple-submicron channel array AlGaN/GaN fin-MOSHEMTs.

A Self-Powered Heterojunction Photodetector Based on a PbS Nanostructure Grown on Porous Silicon Substrate

A photosensor was fabricated based on a lead sulfide (PbS)/porous silicon (Ps) heterojunction. An n-type Si(100) single crystal wafer was used to prepare the Ps using a photo-electrochemical etching method. A PbS nanocrystalline thin film was deposited onto the Ps substrate using a microwave-assisted chemical bath deposition (MA-CBD) technique. The current-voltage (I-V) characteristics of the fabricated PbS/Ps photosensor were studied under dark, 10 mW/cm2, 20 mW/cm2, and 40 mW/cm2 illumination by light. The device shows good response to light even without a bias voltage and the sensitivity when the applied voltage is 0 V decreased from 5.66 × 104 % under 10 mW/cm2 to 1.8 × 103 % when the device is illuminated by 40 mW/cm2 intensity light. The fabricated PbS/Ps photdetector shows a faster response to light of 0.43 sec when the applied voltage and intensity of light were 1.0 V and 40 mW/cm2, respectively. Moreover, the fastest fall time was 0.4 sec obtained for the device that was exposed to 40 mW/cm2 light and biased by 0.75 V.

Gate-Recessed AlGaN/GaN ISFET Urea Biosensor Fabricated by Photoelectrochemical Method

To develop the high sensitive ion-sensitive field-effect-transistor (ISFET) urea biosensors, the AlGaN/GaN heterostructure with high electron sheet carrier concentration was utilized in this paper. Furthermore, the photoelectrochemical etching method and the oxidation method were, respectively, applied to recess the gate region and directly grow the Ga x Al y O3 sensing membrane for enhancing sensing performances. Due to the progress of controlling ability from the gate-recessed region, the resulting characteristics of the gate-recessed AlGaN/GaN ISFET urea biosensors, including transconductance and sensing sensitivity, were obviously improved compared with the planar gate AlGaN/GaN ISFET urea biosensors. The maximum transconductance value and the urea sensitivity of the gate-recessed AlGaN/GaN ISFET urea biosensors were, respectively, improved to 75.9 mS/mm and 18.15 mA/pCurea compared with that of the planar gate ones. Compared with the planar gate structure, the maximum transconductance value and the urea sensitivity of the gate-recessed structure were improved 17.7% and 40.2%, respectively. Furthermore, the urea biosensors were, respectively, measured in the solution with various common interfering ions (glucose, K+, and Na+) to verify stability and reliability.

Wafer-scale porous GaN single crystal substrates and their application in energy storage

Porous GaN has recently attracted much interest due to its high surface area, shift of bandgap and efficient luminescence. However, the porous GaN materials obtained so far are mainly fabricated via an electrochemical etching or a photoelectrochemical etching method. Here, we report the fabrication of wafer-scale (2 inch) porous GaN by a novel and simple high temperature annealing process. A model is proposed, based on scanning electron microscopy as well as the stabilities of the GaN crystallographic plane, to explain the formation mechanism of the porous GaN. Improvement of the crystal quality, enhancement of the optical quality and strain relaxation of porous GaN are confirmed by the HRXRD, PL and Raman spectroscopy results. A three-electrode system based on the porous GaN electrodes is assembled. The good capacitive behavior and superior electrochemical reversibility validate the concept of porous GaN-based supercapacitors and point to their potential in energy storage applications.

Electrochemical impedance spectroscopy analysis of porous silicon prepared by photo-electrochemical etching: current density effect

Electrical impedance characteristics of porous silicon nanostructures (PSiNs) in frequency function were studied. PSiNs were prepared through photo-electrochemical etching method at various current densities (15–40 mA/cm2) and constant etching time. The atomic force microscope images of PSiNs show that pore diameter and roughness increase when current density increases to 35 mA/cm2. The surface roughness subsequently decreases because of continuous etching of pillars, and a second etching process occurs. Photoluminescence spectra show blue and red shift with increasing applied current density that is attributed to PSiNs size. Variations of electrical resistance and capacitance values of PSiNs were measured using electrochemical impedance spectroscopy analysis. These results indicate that PSiNs prepared at 20 mA/cm2 current density have uniform porous structures with a large number of pillars. Furthermore, this PSiNs structure influences large values of charge transfer resistance and double layer capacitance, indicating potential application in sensors.

Enhancing hydrogen sensitivity of porous GaN by using simple and low cost photoelectrochemical etching techniques

This paper reports the studies of Pd Schottky contact on porous n-GaN for hydrogen gas sensor. A simple conventional and low cost photoelectrochemical etching method was used to produce porous GaN with high uniformity. Hydrogen sensor was subsequently fabricated by depositing Pd Schottky contacts onto the porous GaN sample. For comparative study, a standard hydrogen sensor was also prepared by depositing Pd Schottky contacts on the as-grown sample. The Pd/porous GaN sensor exhibited a significant change of current upon exposure to different flow rates of 2% H2 in N2 gas as compared to the standard Pd/GaN sensor. The response increased exponentially with hydrogen flow rate for both sensors, but Pd/porous GaN is more sensitive to hydrogen than that of the as-grown GaN. The values of ideality factor (n), barrier height (φB) and series resistance (Rs) were calculated in both sensors. Barrier heights and series resistance decreased with H2 flow rate while ideality factor increased.

Effective conversion efficiency enhancement of solar cell using ZnO/PS antireflection coating layers

Abstract Zinc oxide (ZnO) film was deposited on a porous silicon (PS) layer using a radio frequency sputtering system while the PS layer was prepared by a photoelectrochemical etching method. The ZnO/PS layers were found to be an excellent antireflection coating (ARC), exhibiting exceptional light trapping at wavelengths ranging from 400 to 1000 nm because of their lowest effective reflectance. This, in turn, leads to increase the efficiency of solar cell to 18.15%. The ZnO film was highly oriented with the c -axis perpendicular to the PS layer. The average crystallite size of the PS and ZnO/PS layers were 17.06 and 17.94 nm, respectively. Photoluminescence emission peaks proved the nanocrystalline characteristic of the PS layer and the ZnO film. Raman measurements of the ZnO/PS layers were determined at room temperature and indicate that a high-quality ZnO nanocrystalline film was formed. In the current paper, ZnO/PS ARC layers are attractive and offer a promising technique to produce high-efficiency, low-cost solar cells.

Novel Use of Columnar Porous Silicon Carbide Structures as Nanoimprint Lithography Stamps

Columnar porous Si-face 6H-SiC substrates were prepared by a photo-electrochemical etching method and applied as nanoimprint lithography (NIL) stamps. The diameter of the pores in the porous region was about 20 nm and the center-to-center separation between pores was about 60 nm. The columnar porous SiC substrates were subjected to a vapor phase silanization treatment whereby a monolayer of perfluorooctyltrichlorosilane (FOTS) was deposited in order to keep the stamps from sticking to the substrates during the imprint step. Subsequently, the porous SiC stamps were used to imprint polymethylmethacrylate (PMMA) at elevated temperatures and pressures. The imprinted PMMA could then be used to transfer the nanopattern on the columnar porous SiC to other substrates for various purposes; e.g. templates for GaN regrowth, catalysts for nanowire growth by vapor-liquid-solid type methods (VLS), etc. SiC is not typically used for NIL stamps since etch processing of SiC is less mature than that of Si. However, as demonstrated here, there is no reason why SiC cannot be used as a material for NIL stamps. The superior mechanical properties to Si make the use of SiC alluring as a master template for NIL processing.

Light Output Enhancement of GaN-Based Roughened LEDs Using Bias-Assisted Photoelectrochemical Etching Method

A bias-assisted photoelectrochemical (PEC) etching method is developed to roughen the p-GaN surface of GaN-based light-emitting diodes (LEDs). According to the atomic force microscopy images obtained, the morphology of the p-GaN surface can be effectively roughened by using the bias-assisted photoelectrochemical etching method. The relative threshold voltage and leakage current of LEDs with and without the PEC treatment were virtually similar, indicating that the electrical performances had not been damaged by the bias-assisted PEC etching method. The enhancement of the light output power of LEDs subjected to the PEC treatment with durations of 5, 10. and 15 min compared with conventional LEDs had been determined to be 13.5, 19.1, and 22.7%, respectively. The foregoing results evidently demonstrated that an increase in the light output power critically depends on the surface morphology.

The Growth of Porous Layer on Resistive P-Type Silicon in HF/Ethylene Glycol under Illumination

In the present work, a photoelectrochemical etching method had been performed on resistive p-type Si (100) to eliminate the instability attributed to the high resistivity of substrate comparing to that of electrolyte. The anodization of p-type Si with resistivity ranging from 10 Ωcm to 30 kΩcm was done in HF/ethylene glycol. The resistivity of electrolyte was experimentally determinated by high frequency impedance measurements. As anodization proceeds structures of increasing characteristic size are formed then a steady state is reached, where macropore grow parallel. It shows that pore diameter increases with increasing HF concentration. Whereas, under laser He-Ne irradiation both of nanopores and macropores are observed during the anodization. The nanoporous layer showed to be varying with the light intensity and the anodization time. The proprieties of the porous silicon were investigated by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and energy-dispersive X-ray (EDX).