UV-assisted Electrochemical Etching Research Articles

Characterization of porous InGaN-based metal-semiconductor-metal

In this study, the characteristics of metal-semiconductor-metal (MSM) photodetector based on a porous In0.27Ga0.73N thin film were reported. Nanostructured porous film was synthesized using the UV-assisted electrochemical etching technique. The formed pores were dissimilar in terms of shape and size. The effect of annealing in the range of 300e500 C on Pt/In0.27Ga0.73N was investigated by IeV measurements. Schottky barrier height was at maximum value under 500 C. The fabricated MSM photodetector shows photovoltaic characteristics in the green region of the electromagnetic spectrum. The device responsivity increased with increasing the bias voltage. Moreover, the rise and recovery times of the device were investigated at 10 mW cm 2 of a 550 nm chopped light. Finally, the sensitivity and quantum efficiency were also investigated.

Investigation on the Effect of Current Density on Porous GaN Fabricated by UV-assisted Electrochemical Etching

Investigation on the Effect of Current Density on Porous GaN Fabricated by UV-assisted Electrochemical Etching

Preparation and photoluminescence of self-standing nanoporous InGaN/GaN MQWs via UV-assisted electrochemical etching

The self-standing InGaN-based multiple quantum wells (MQWs) thin films with the vertically aligned nanoporous InGaN/GaN layer, were electrochemically etched in nitric acid (HNO 3 ) solution under ultraviolet (UV) light, and then transferred to stainless steel cloth and quartz substrates, respectively. Compared to the as-grown sample, the etched and transferred thin films show an enhanced and blue-shift photoluminescence (PL) emission. The PL enhancement is attributed to the improved internal quantum efficiency (IQE) which is ascribed to the improved crystalline quality of MQWs, and the increased light extraction efficiency (LEE) which is ascribed to the high light-extracting surface area and light-guiding effect of the vertically aligned nanoporous InGaN/GaN structure. And the blue-shift can be attributed to stress relaxation of MQWs and variable In content in InGaN layer. PL spectra of As-grown, etched and two transferred InGaN-based MQWs. • The self-standing nanoporous InGaN/GaN MQWs are prepared by a UV-assisted electrochemical etching. • Compared to the as-grown sample, the etched and transferred thin films show an enhanced and blue-shift PL emission. • Among the samples, the transferred thin films show the largest PL intensity.

Morphological, Structural and Optical Characteristics of Porous GaN Fabricated by UV-Assisted Electrochemical Etching

The fabrication of porous GaN (PGaN) by UV-assisted electrochemical etching with a variations of current densities (40, 60, and 80 mA/cm2) for 60 min in electrolytes consisting of 4% KOH are reported. Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-Ray (EDX), Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) were used to characterize the morphological and structural characteristics of the PGaN. All PGaN sample prepared by electrochemical etching technique produced a hexagonal-like pore shape. FESEM images demonstrated that the pore uniformity and porosity are affected significantly by the current density. The PGaN sample fabricated with 80 mA/cm2 produces a uniform and high porosity structure compared to other PGaN sample. This shows that the morphology and structural characteristic of PGaN are increase with the increase of current density. The EDX result revealed significant Ga and N atom presence in all samples. However, the O atom only presence in sample etched with 80 mA/cm2 implying that the etching process is occur vigorously in this sample. The AFM verified that the surface roughness and the pore depth are increased as current density increased. There were relatively large variations of the peak intensities for 2Theta-scan patterns as exposed by XRD. The peak shift for PGaN sample relative to as-grown was inconsistent and the changed was relatively small. Raman intensity found to be enhanced with the increase in current density and among the PGaN sample, the E2(high) peak for sample prepared with 60mA/cm2 and 80mA/cm2 was observed to be slightly shifted to lower frequency. The PL spectra displayed that the porosity has high impact on the PL peak intensity. . Overall, this proved that with the usage of low power UV light, the pore structure still can be produced as good as pore structure fabricated with high power UV light.

Effect of KOH Concentration on the Properties of Undoped Porous GaN on Sapphire Substrate Prepared by UV assisted Electrochemical Etching

Effect of KOH Concentration on the Properties of Undoped Porous GaN on Sapphire Substrate Prepared by UV assisted Electrochemical Etching

Photoluminescence properties of etched GaN-based LEDs via UV-assisted electrochemical etching

A GaN-based light emitting diode (LED) with an InGaN/GaN multiple quantum well (MQW) structure was electrochemically etched in an oxalic acid solution under ultraviolet (UV) light and fabricated into nanoporous structure for the first time. Compared to that of the as-grown GaN-based LED, photoluminescence (PL) emission of the etched LEDs shows (i) a marked blue-shift which is ascribed to a stress relaxation and a relative decrease of indium (In) component in the MQW layer, (ii) a two-fold enhancement of PL intensity which results from the increase of light-extracting surface area, light-guiding effect, and internal quantum efficiency.

Porosity-induced weakening of piezoresponse in GaN layers by means of piezoelectric force microscopy

Nanoporous (NP) GaN thin films with low nucleation density were fabricated via UV-assisted electrochemical etching approach. Under different applied biases, two NP samples with different porosities were fabricated. Piezoelectric characteristics of the fabricated samples were investigated using piezoresponse force microscopy. It was found that the nanopores have great influence on its piezoelectric characteristics such as weakening of piezoresponse and change of polarization orientation. During the performance of devices, the weakening of piezoresponse should be propitious to the optoelectronic and electronic stabilities of GaN-based devices.

Luminescence evolution of porous GaN thin films prepared via UV-assisted electrochemical etching

Porous gallium nitride (GaN) thin films with different surface morphologies and free carriers properties were fabricated from Si-doped GaN thin films using ultra-violet assisted electrochemical etching approach under various etching voltages. Fluctuation of luminescence signals was observed in the photoluminescence spectra of porous GaN thin films. Taking advantage of the spectral sensitivity of infrared attenuated total reflection spectroscopy on semiconductor materials, roles of free carriers and porous structure in controlling luminescence properties of GaN were investigated thoroughly. The results revealed that enhancement in luminescence signal is not always attained upon porosification. Although porosification is correlated to the luminescence enhancement, however, free carrier is the primary factor to enhance luminescence intensity. Due to unavoidable significant reduction of free carriers from Si-doped GaN in the porosification process, control of etching depth (i.e., thickness of porous layer formed from the Si-doped layer) is critical in fabricating porous GaN thin film with enhanced luminescence response.

Formation and Optical Studies of Porous GaN Thin Films via UV-Assisted Electrochemical Etching Approach

This paper presents the investigation of porous gallium nitride (PGaN) thin films by ultra-violet (UV)-assisted electrochemical etching at various etching durations. The etching process was performed in potassium hydroxide aqueous solution under illumination of 150 W xenon lamp. The surface morphology and cross-section of the PGaN thin films were examined by scanning electron microscopy. Increased etching duration resulted in a more homogeneous pore distribution. Results showed that the etching duration strongly influences the layer characteristic of porous structure. Infrared (IR) and Raman studies were performed to investigate the optical properties of PGaN. IR spectroscopy revealed that the PGaN thin films exhibit distinctive IR spectra as compared to the as-grown GaN thin film. The number of interference fringes in the non-reststrahlen band is correlated to the film thickness of as-grown and PGaN thin films. The Raman measurements clearly reveal two forbidden optical phonon modes observed in all the PGaN thin films. This result indicates the crystal disordering in the films. Additionally, the findings show that the intensity of these forbidden modes becomes stronger with increasing etching duration.

Fabrication and characterization of metal–semiconductor–metal photodetector based on porous InGaN

In this study, the characteristics of metal–semiconductor–metal (MSM) photodetector based on a porous In0.27Ga0.73N thin film were reported. Nanostructured porous film was synthesized using the UV-assisted electrochemical etching technique. The formed pores were dissimilar in terms of shape and size. The effect of annealing in the range of 300–500 °C on Pt/In0.27Ga0.73N was investigated by I–V measurements. Schottky barrier height was at maximum value under 500 °C. The fabricated MSM photodetector shows photovoltaic characteristics in the green region of the electromagnetic spectrum. The device responsivity increased with increasing the bias voltage. Moreover, the rise and recovery times of the device were investigated at 10 mW cm−2 of a 550 nm chopped light. Finally, the sensitivity and quantum efficiency were also investigated.

Nanoporous InGaN of high In composition prepared by KOH electrochemical etching

The fabrication of porous InGaN of high In composition ~47% using UV-assisted electrochemical etching in a diluted solution of KOH is demonstrated for the first time. In this paper, the effect of etching time on the morphology of porous InGaN was investigated using field emission scanning electron microscopy (FE-SEM). Pore size and density were found to increase with increasing etching time. In addition, the etching activity at grain boundaries became significant for longer etching periods in which more defective region at grain boundaries had been etched. The reduction in dislocation density due to the etching process was confirmed by a decreased value of the full width at half maximum (FWHM) from high resolution x-ray diffraction (HR-XRD) rocking curve measurements for all porous samples. Porous samples exhibited red-shift characteristics in photoluminescence (PL) spectra with respect to the as-grown sample due to relaxation of compressive stress. Furthermore, the PL intensity of porous samples showed stronger signals relative to the as-grown sample, which is attributed to both the reduction of dislocation density and multiple light scattering from the crystallite sidewalls. Such properties indicate the potential of porous InGaN for applications in optical and sensor devices.

Structural properties of porous In0.08Ga0.92N synthesized using photoelectrochemical etching

This paper presents the morphology and structural studies of as-grown and porous In0.08Ga0.92N/AlN/Si thin films prepared by UV-assisted electrochemical etching under various etching durations. The morphology and structural properties of the as-grown and porous thin films were investigated. The atomic force microscope, field emission scanning electron microscope images, and X-ray diffraction measurements revealed that the films have smooth and uniform surface over a large region with wurtzite phase. The diffraction peaks of the post-etched samples were shifted to a higher angle region compared to the pre-etched sample indicating a change in composition of InGaN layer as In incorporation of the layer decreases, subsequently decreasing the lattice constant c (approach to cGaN) of the alloy with compressive strain.

Enhanced Properties of Porous GaN Prepared by UV Assisted Electrochemical Etching

The structural and optical properties of porous GaN films on sapphire (0001) prepared by UV assisted electrochemical etching were reported in this study. SEM micrographs indicated that the shapes of the pores for both porous samples are nearly hexagonal. As compared to the as-grown GaN films, porous layers exhibit a substantial photoluminescence (PL) intensity enhancement with red-shifted band-edge PL peaks associated with the relaxation of compressive stress. The shift of E2(high) to the lower frequency in Raman spectra of the porous GaN films further confirms such a stress relaxation.

Enhanced optical properties of porous GaN by using UV-assisted electrochemical etching

In this paper we report the fabrication of porous GaN by UV-assisted electrochemical etching with direct current densities of 5, 10 and 20 mA/cm 2 for 20 min in electrolytes consisting of aqueous HF and ethanol C 2H 5OH (1:4). Scanning electron microscopy (SEM) demonstrates that current density has significant effect on the size and shape of the pores. Raman spectra of both as-grown and porous GaN exhibit phonon mode E 2 (high), A 1 (LO), A 1 (TO) and E 2 (low). There was a red shift in E 2 (low) and E 2 (high) and blue shift in A 1 (LO). The red shift in E 2 (high) indicates a relaxation of compressive stress in the porous GaN surface with respect to the underlying single crystalline epitaxial GaN. Peak intensity of photoluminescence (PL) spectra of the nanoporous GaN samples was observed to be enhanced and the crystal quality was improved with increase in etching current density as compared to as-grown GaN.

Synthesis Porous GaN by Using UV-assisted Electrochemical Etching and Its Optical Studies

The PL of porous GaN sample shows higher intensity with smaller FWHM and red-shifting relative to the as-grown sample. The energy gap for porous GaN sample was smaller compare to the as-grown sample. The SEM surface image of UV-assisted electrochemical etching process is shown a shape and size of pore which was formed on the surface of the GaN, therefore the shape of pores formed was in spherical shape. The size of the pores formed has diameter as small as 85 nm. Two PL peaks were observed in the as-grown and porous GaN sample. For the as-grown GaN, the higher peak was observed at “361.946 nm” and the other at “723.739 nm” which is in UV and red luminescence region respectively. The FWHM is “8.198 nm” at “361.946 nm”. For the porous GaN, the higher peak was observed at “364.235 nm” and at “728.039 nm”, so their FWHM are “4.244 nm” and “8.926 nm” respectively. The peaks of porous sample were red-shifted at “2.289 nm and 4.30 nm” respectively compare to the peaks of the as-grown GaN. PL intensity of the porous samples was observed to be increased. Raman peaks representative to the wurtzite GaN crystal, namely E 2 (low) at 142.426 cm -1 , E 2 (high) at 568.771 cm -1 , and A 1 (LO) at 736.769 cm -1 were clearly observed.

Effect of carrier density on the surface morphology and optical properties of nanoporous GaN prepared by UV assisted electrochemical etching

Nanoporous GaN samples were prepared by UV-assisted electrochemical etching of Si-doped GaN using the HF-based electrolyte. The Si doping density in the as-grown GaN samples was varied from 1×1016to1×1019cm−3. The surface morphology and optical quality of these nanoporous GaN films are controlled by the doping density in the as-grown films. The scanning electron microscopy results reveal that the average pore size can be tuned from 100to45nm by increasing the carrier density in the as-grown GaN films from 1×1016to1×1019cm−3. Photoluminescence (PL) measurements indicate that the nanoporous GaN films exhibit a higher PL intensity with redshifted band-edge PL peak compared to the as-grown GaN films. The nanoporous GaN prepared from highly doped sample gives highest PL intensity and stress relaxation due to the presence of smallest size nanopores. The redshift of the E2(high) phonon mode in the Raman spectra of nanoporous GaN prepared from heavily Si-doped samples shows a significant relaxation of the compres...

Comparative Study of Optical Properties of Nanoporous GaN Prepared by UV-Assisted Electrochemical and Electroless Etching

not Available.

Influence of Rapid Thermal Annealing on the Luminescence Properties of Nanoporous GaN Films

Nanoporous GaN films were prepared by UV-assisted electrochemical etching. It was observed that by employing rapid thermal annealing (RTA), optical properties of porous GaN films could be considerably improved. The nanoporous GaN films were subjected to RTA within the temperature range of 500-1100°C under nitrogen and oxygen ambient. The band-edge photoluminescence (PL) intensity from the porous GaN films showed a monotonic increase with the annealing temperature up to 1000°C in N 2 . However, the band-edge PL intensity showed a drastic reduction for the porous samples annealed under oxygen ambient. Besides this, investigation of the effects of annealing conditions on Eu-implanted nanoporous GaN in N 2 and O 2 ambient was also carried out. We have observed that annealing in N 2 significantly enhances the Eu-related red luminescence around 621 nm, which implies that annealing conditions could play an influential role for light extraction from nanostructured GaN surfaces.

Investigation of optical properties of nanoporous GaN films

In this study, we have investigated the optical properties of nanoporous GaN films on sapphire (0 0 0 1) prepared by UV-assisted electrochemical and electroless etching. Using various etching conditions, we can control the average pore size, pore depth and the density of pores on the GaN surface. Scanning electron microscopy (SEM) measurements reveal the nature of the pore morphology and microstructures. Optical properties of these nanoporous films have been studied using micro-photoluminescence and micro-Raman scattering. As compared to the as-grown GaN films, nanoporous layers exhibit a substantial photoluminescence (PL) intensity enhancement with red-shifted band-edge PL peaks associated with the relaxation of compressive stress. The red shifted E 2 phonon peak in the Raman spectra of the porous GaN films further confirms such a stress relaxation. Microscopic optical measurements also suggest that light extraction from porous GaN surface is enhanced by such nanopatterning.