Synthesis and characterization of laser annealed nanoporous silicon-zinc oxide nanoclusters for ultraviolet photodetector application

The main purpose of this study was to synthesize a series of nanoporous silicon (n-PSi) samples on n-type Si (111) wafer using the photo-electrochemical etching (PECE) method, which was effective for the fabrication of a metal-semiconductor-metal (MSM) ultraviolet photodetector. Samples were prepared at fixed etching time (30 min) under varying PECE operating parameters, which included differential current densities (15, 30 and 45 mA/cm2) and variable chemical ratios to achieve optimum growth. The structural, morphological and optical properties of the as-prepared PSi samples were characterized by different analytical techniques. The optimum etching parameters for the growth of n-PSi samples comprise of etching time of 30 min, current density of 45 mA/cm2 and chemical ratio of 2:1:1. The objectives of this study were achieved in three phases. First, a layer of zinc oxide (ZnO) nanoclusters was deposited on the optimally grown n-PSi sample by means of radio frequency (RF) sputtering. The thicknesses of the deposited ZnO nanoclusters layers on n-PSi were varied between 300 nm and 500 nm for annealing temperatures ranging from 600 oC to 900 oC. The optimum thickness and temperature were determined to be 300 nm and 700 oC, respectively. Secondly, platinum (Pt) electrodes were deposited on the n-PSi/ZnO NCs structure via radio frequency sputtering to obtain the MSM (Pt/n-PSi/ZnO NCs/Pt) ultraviolet photodetectors. Finally, the performances of fabricated ultraviolet MSM photodetectors were evaluated using current-voltage (I-V) measurement. The optimum n-PSi and n-PSi/ZnO NCs samples were annealed using a Nd-YAG laser under several shots (pulses) to determine their influence on the structural, morphological, optical and electrical features of the n-PSi/ZnO NCs samples. The photoluminescence spectra of the optimally synthesized n-PSi/ZnO NCs exhibited an intense near band edge emission (violet band centred at 380 nm for bandgap energy of 3.26 V). The I-V characteristics of the fabricated MSM ultraviolet photodetectors were examined in the dark and under ultraviolet light (380 nm) illumination. The results revealed that laser annealing can significantly improved of the performance of the fabricated Pt/n-PSi/ZnO NCs/Pt ultraviolet photodetector in terms of high responsivity (6.35 A/W), photosensitivity (3772.92) as well as faster response time (0.30 s) and recovery time (0.26 s). It was concluded that the proposed MSM ultraviolet photodetectors could be advantageous for various optoelectronic applications

The effect of Nd : YAG laser beam on aluminium surface coated with Fe-SiC

Laser ablation on aluminium base coated with Fe-SiC is reported. A qswitched Nd:YAG laser was employed as a source of energy. The fundamental wavelength of the laser beam is 1064 nm with output energy of 100 mJ and pulse duration of 10 ns. The laser was conducted in repetitive mode with frequency rate of 1 Hz. The laser was focused to induce plasma formation. Pure aluminium plate was employed as a substrate for laser ablation. Metal element iron (Fe) and ceramic material silicon carbide SiC were selected to be as laser ablation elements. Both of the elements were mixed together in a ratio of 2:1 (Fe:SiC). Two step deposition techniques were chosen in this work to predeposite the aluminium substrate. The substrate was painted with cohesive material gum before powder spray coating on it. The predeposit aluminium was then exposed with focused laser at various numbers of pulses (1 – 13 pulses). The created material was examined via scanning electron microscope (SEM), x-ray diffraction (XRD) machine and microhardness Vicker HV machine. The microstructure of the created surface was examined via SEM and the results showed the effect of homogenized resolidified area. The plasma temperature is much higher than the melting point of the laser ablation material Fe and SiC thus immediately after plasma interaction with coating materials most of them are melted. The fluid flow over the surface and resolidified during cooling. However the melting temperature between Fe, SiC and Al are different, this allows new composite formation during quenching. The formation of such new composite is identified through XRD analysis. Inherently, several new composites are revealed such as Al- Fe-Si, SiAl and Fe-Si. The formation of such new composite is also indicators for the increment in the strength of the created materials. This is validated by measuring the hardness of the created material. Apparently, the hardness of the modified surface is confirmed to be two times greater than the original substrate

Effect of etching time on optical and morphological features of N-type porous silicon prepared by photo-electrochemical method

Achieving efficient visible photoluminescence from porous-silicon (PSi) is demanding for optoelectronic and solar cells applications. Improving the absorption and emission features of PSi is challenging. Photo-electro-chemical etching assisted formation of PSi layers on n-type (111) silicon (Si) wafers is reported. Samples are prepared at constant current density (~30 mA/cm2) under varying etching times of 10, 15, 20, 25, and 30 min. The influence of etching time duration on the growth morphology and spectral properties are inspected. Room temperature photoluminescence (PL) measurement is performed to determine the optical properties of as-synthesized samples. Sample morphologies are imaged via Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The thickness and porosity of the prepared samples are estimated using the gravimetric method. The emission and absorption data is further used to determine the samples band gap and electronic structure properties. Results and analyzed, interpreted with different mechanisms and compared

The effects of the ambient liquid medium on the ablation efficiency, size and stability of silver nanoparticles prepared by pulse laser ablation in liquid technique

Silver (Ag) nanoparticles (NPs) were synthesized by pulsed laser (Nd:YAG, 1064 nm) ablation of individual target in various solutions. The influence of deionized water (DIW), ethanol and Polyvinylpyrrolidone (PVP) as ambient medium on the fundamental aspects such as ablation efficiency, particle size and stability of Ag NPs was studied. UV-vis spectrophotometer and transmission electron microscopy (TEM) were used to study the optical characterization and morphological analysis of all the synthesized samples, respectively. Preparation in DIW was carried out as a reference sample. The experiments demonstrated that ablation efficiency and stability of NPs in ethanol medium are lowest than those prepared in PVP medium and the reference sample. PVP medium led to higher stability, lower ablation efficiency and finer average particle size compared to reference sample

Photo-electrochemically synthesized light emtting nanoporous silicon based UV photodetector: influence of current density

Nanoporous silicon (n-PSi) with diverse morphologies was prepared on silicon (Si) substrate via photo-electrochemical etching technique. The role of changing current density (15, 30 and 45 mA cm−2) on the structure, morphology and optical properties was determined. As-prepared samples were systematically characterized using XRD, FESEM, AFM and photoluminescence measurements. Furthermore, the achieved n-PSi sample was used to make metal–semiconductor–metal (MSM) UV photodetector. The performance of these photodetectors was evaluated upon exposing to visible light of wavelength 530 nm (power density 1.55 mW cm−2), which exhibited very high sensitivity of 150.26 with a low dark current. The achieved internal photoconductive gain was 2.50, the photoresponse peak was 1.23 A W−1 and the response time was 0.49 s and the recovery time was 0.47 s. Excellent attributes of the fabricated photodetectors suggest that the present approach may provide a cost effective and simple way to obtain n-PSi suitable for sundry applications

Photophysical performance of radio frequency sputtered Pt/n-PSi/ZnO NCs/Pt photovoltaic photodetectors

The effect of the annealing temperature on the photoelectrical properties of the nanoporous silicon/zinc oxide nanocrystallites-based (Pt/n-PSi/ZnO NCs/Pt) photodetector was investigated. Different morphologies of 3D ZnO were synthesized onto the n-PSi substrates via radio frequency (RF) sputtering in the absence of a catalyst. The synthesis of ZnO NCs was controlled by varying the growth temperature between 600–700 °C and 800–900 °C. The effect of the synthesis temperature on the structural, morphological, and optical properties of the n-PSi/ZnO NCs was systematically studied using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence spectroscopy (PL) techniques. The roughness was found to be dependent on the anodization current density. The optimal n-PSi/ZnO NCs-based metal-semiconductor-metal UV detector (MSM) was fabricated at 700 °C. The fabricated device showed a high sensitivity of 1007.14, an internal photoconductive gain of 11.07, and a responsivity of 5.99 A/W with a low dark current when illuminated with 380 nm light (1.55 mW/cm2) at +5 V bias voltage. In addition, the response and recovery times were determined to be 0.34 and 0.22 s, respectively. This approach offers a cost-effective substrate and simple synthesis method to improve the growth of the n-PSi/ZnO NCs and demonstrates the successful fabrication of nanoscale photodetectors with potential application in nano-optics devices

Photophysical performance of Nd-YAG annealed Pt/n-PSi /Pt photovoltaic photodetectors at different laser energy

This study investigates the electrical and photoresponse properties of Nd-YAG annealed Pt/n-PSi/Pt photodetectors. A porous silicon (PSi) layer was deposited on a single crystalline n-type Si via photoelectrochemical etching in aqueous hydrofluoric acid at 45 mA cm−2 for 30 min. Annealing of the n-PSi layer was conducted using a Q-switching Nd:YAG laser at different fluence laser energies (20, 30, 40, 60 mJ cm−2) with a pulse duration of 10 ns. The effect of Nd:YAG laser irradiation on the morphological and structural properties of the deposited n-PSi layer was determined. The n-PSi sample synthesized at 40 mJ cm−2 showed the maximum average discrepancy. The photodetectors fabricated using such materials showed very high sensitivity (1527.9) and low dark current (2.58 × 10−4 A) with an internal photoconductive gain of 16.27, photoresponse of 3.1 A W−1, response time of 0.29 s, and recovery time of 0.45 s. These exceptional properties of the fabricated photodetectors indicate that the laser annealing approach is a viable tool for the synthesis of n-PSi that is suitable for various applications

Photo-electrochemically synthesized light emtting nanoporous silicon based UV photodetector: influence of current density

Nanoporous silicon (n-PSi) with diverse morphologies was prepared on silicon (Si) substrate via photo-electrochemical etching technique. The role of changing current density (15, 30 and 45 mA cm-2) on the structure, morphology and optical properties was determined. As-prepared samples were systematically characterized using XRD, FESEM, AFM and photoluminescence measurements. Furthermore, the achieved n-PSi sample was used to make metal-semiconductor-metal (MSM) UV photodetector. The performance of these photodetectors was evaluated upon exposing to visible light of wavelength 530 nm (power density 1.55 mW cm-2), which exhibited very high sensitivity of 150.26 with a low dark current. The achieved internal photoconductive gain was 2.50, the photoresponse peak was 1.23 A W-1 and the response time was 0.49 s and the recovery time was 0.47 s. Excellent attributes of the fabricated photodetectors suggest that the present approach may provide a cost effective and simple way to obtain n-PSi suitable for sundry applications

High-performance nanoporous silicon-based photodetectors

A series of porous silicon (PSi) samples was prepared using photoelectrochemical etching (PECE) method with optimum current density of 45 mA/cm2. The as-prepared PSi samples were characterized to determine the influence of the etching time (15, 25 and 30 min) on their morphology and electrical properties. The percentage of porosity was estimated via gravimetric analysis. The band gap of the fabricated PSi was ≈2.22 eV. Upon their use to fabricate metal-semiconductor-metal (MSM) ultraviolet photodetectors (UVPD), the fabricated PSi revealed excellent stability and reliability under repetitive shots at 530 nm. Furthermore, very fast rise time (≈0.28 s) was obtained at a bias of 1 V under visible light (530 nm) illumination