Introduction

Gold nanoparticles (AuNPs) can be created by alternative techniques, such as physical irradiation process, laser ablation, electrochemical, chemical methods, and biological method, microorganisms, plants [1,2,3]. As a result nanoparticles/porous Si (NP/PS) systems made of metal have been investigated in enhancing their sensing capabilities [4, 5] and luminescent [6,7,8] PS substrates surface enhanced Raman scattering covered in noble metal nanoparticles, such as Gold and Silver, have also been widely researched [9,10,11,12,13,14]. Hydrodynamic disturbances on polished Si substrates, also the thin-film thickness fluctuations, voids occur in the film, with little effect from the substrate topography [15,16,17,18,19,20,21]. Surface Plasmon Resonance (SPR) is one of the most important optical properties of metallic nanoparticles. It is formed of collective oscillations of conduction electrons caused by the electromagnetic field of incident light [22]. Nanoparticles have several properties which aren't found in bulk materials [23]. The shape and size of nanoparticles have a profound effect on their properties (electrical, optical, and magnetic) [24]. AuNPs are interesting nanomaterial with a large range of applications in basic research. [25, 26] AuNPs, for example, have been employed in single electron devices and scanning laser microscopy studies of cellular mechanisms [27, 28]. Ultrasensitive biosensors, catalysis in the manufacture of self-assembling nanomaterial, photovoltaic devices, and nonlinear optics [29,30,31,32,33,34]. Nanoscale materials can be used in a range of applications, such as optomechanical sensors, chemicals, and natural cycles [35,36,37]. Laser ablation in liquids has recently been mentioned as a possible source of nanoparticles by a few authors [38,39,40,41]. Gold nanoparticles (AuNPs) are particularly essential in metal nanoparticles due to their great effectiveness of (SPR) [42,43,44,45]. AuNPs have electrical, mechanical, and physical properties due to their wide range of applications [46,47,48]. The absorption of AuNPs is influenced by their diameter, the electrical insulator's center, and the chemical environment [49, 50]. In AuNPs, the conduction band and valence bar are closely enough, permitting electrons to pass freely across them. These free electrons absorb the Surface Plasmon Resonance (SPR), which also is formed by the amplitude fluctuating of the electrons of nanoparticles in resonance with the optical wave [51, 52]. A new approach to produce nanoparticles that can be employed in a variety of applications is to use laser ablation in liquid. PLAL has been used to generate a variety of nanoparticles, including metals, oxides, alloys, and semiconductors [53,54,55,56,57,58,59]. In the current work, AuNPs that were prepared using laser ablation technology approach and deposited on PS to create ultra-high sensitivity photo detector nanostructures. Investigations have been done into the electric, optical, and structural characteristics.

Experimental details

AuNPs have been made using laser ablation (Nd:YAG) 1 Hz pulse repetition rate with wavelengths of 1064 nm and 532 nm, energies (600, 800, 1000)mJ. High pure gold plate was washed by ethanol and distilled water then placed in vessel with solution of PVA and distilled water after mixing it to the point of homogeneity using the stirrer. Production of gold nanoparticles in PVA by nanosecond laser incidence on gold plate. To obtain an appropriate concentration of gold nanoparticle solution, this experiment has been carried out multiple times, via casting technique the Au/PVA in different energies solution dripping on the porous silicon carefully prepared using photoelectrochemical etching (PECE) in 18 min. The (J–V) in dark and (Jph–V) in light properties of the structural elements Si, PS and AuNPs/PS were investigated, taking into account the light and dark current density. These samples were illuminated with a halogen lamp at a range of light power density of (5, 20, 60, and 125) mW/cm2 with reverse voltages between (− 6 and + 6) Volt.

Results and discussion

UV–Vis absorption-based solutions using PVA were investigated for their effectiveness in both 532 nm and 1064 nm with (600, 800, 1000) mJ and 500 pulse Fig. 1 their results are compared. The intensification of the increase in laser energy can also lead to an increase in absorption spectra attributed to the rise in nanoparticles concentration. Absorbance is calculated using Beer-Lambert equation and the concentration of the solution. The formation of some more than one gap in nanoparticles, on the other hand, can result in a particle size increase. In this work, PVA 1064 nm was selected for better results, as from Table 1 and compared with the rest of the table it was seen, the spectrum shows strong absorption between (500 and 550) nm and shifts toward shorter wavelengths (blue shift) with an increasing laser energy due to reduce the nanoparticles size.

Fig. 1
figure 1

Absorption spectra of AuNPs colloidal prepared with various laser energies, at 500 shots. a 532 nm, b 1064 nm laser wavelength

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Table 1 The UV–Vis characteristics for Au NPs in PVA prepared by laser ablation 532 nm and 1064 nm laser wavelength
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XRD was used to investigate the crystalline degree of AuNPs/PS at 1064 nm and 532 nm in 1000 mJ. The XRD measurements for PS show a very strong peak in 2θ = 69°, 60° in 532 nm and 2θ = 69°, 70° in 1064 nm for 1000 mJ observed through Fig. 2. There are peaks in the XRD pattern for the AuNPs/PS layers, from the creation of crystalline AuNPs on the PS substrate, and the results for the AuNPs/PS layers we can see the layers exhibited a peak at 2θ = 37.900° to the PS (111) layer in 532 nm 2θ = 38.200° in 1064 nm matching to the (111) crystal planes of crystalline AuNPs, demonstrating the discovery of AuNPs when deposited on PS.

Fig. 2
figure 2

X-ray diffraction patterns of the Au NPs/PS prepared by laser ablation with a 532 nm laser wavelength, b 1064 nm laser wavelength

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Table 2 displays the discovered crystallite sizes in Au/NPs/PS in 532 nm in 1000 mJ and PS etched in 18 min calculated by Scherrer equation show a considerable increase in crystallite size with decreasing in FWHM in all wavelengths.

Table 2 Values obtained from measurements using XRD peaks for Au NPs/PS in PVA prepared by laser ablation with 532 nm and 1064 nm laser wavelength
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Different laser energies (600 mJ, 800 mJ, and 1000 mJ) were used to examine the PL spectra of porous silicon and AuNPs at room temperature, at two wavelengths 532 nm and 1064 nm as Fig. 3. There is only one unique emission band at (581, 588, 591) nm in 532 nm, and 1064 nm (581, 582, 588) nm. As laser pulse energy increases from 400 mJ, 600 mJ, to 1000 mJ. When comparing of two crystals, the crystal with the shorter wavelength 532 nm has a larger refractive index with longer wavelengths and lower energies, and we note in it the greatest wavelength in the visible region at 591 nm and peaks shifted to higher wavelength.

$$E = \frac{hc}{\lambda }$$
(1)
$$n = \sqrt {1 + \frac{A}{{B + E_{{\text{g}}} }} }$$
(2)

A = 13.6 eV and B = 3.4 eV; h, Plank constant; c, speed of light.

Fig. 3
figure 3

PL spectra of the Au/NPs porous silicon, different laser pulse energies, Nd: YAG laser at a 532 nm, b 1064 nm laser wavelength

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Using Eq. (1) [60], as the energy rate rises, the band gap (Eg) narrows, and the wavelength increases as a result the quantum confinement phenomenon when the refractive index raises Eq. (2) [61, 62]. Excitation value for PL spectra of 591 nm in 532 nm and 585 nm in 1064 nm is visible, showing a change to blue in the band gap when contrasted to bulk Si, for which the quantum confinement effect is responsible as shown in Table 3.

Table 3 Values of PL peaks AuNPs/PS prepared with varying laser pulse energies at (a) 532 nm laser wavelength (b) 1064 nm laser wavelength
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The particle size of AuNPs is seen in TEM images in Fig. 4. The AuNPs were created using a laser with pulse energy of 1000 mJ, 500 pulse rate in two crystal wavelength 532 nm and 1064 nm. It can be seen that prepared AuNPs nearly has a spherical shape. Complementary contrast was visible in TEM images, confirming the creation of the core shell structures, it can be suggested that the uniform layer covers the spherical core the second phase. When comparing the two crystals, it becomes clear that at the wavelength of 532 nm the size of the particles is greater than 1064 nm.

Fig. 4
figure 4

TEM image for AuNPs colloidal prepared using PLAL synthesis at E = 1000 mJ a 532 nm, b 1064 nm laser wavelength

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The SEM images of the AuNPs Porous silicon structure in two crystals of different wavelengths and constant energy were used at 1000 mJ and the etching time of the porous silicon was fixed in 18 min the particle size increase with the crystal of 532 nm and decrease with 1064 nm so it is an inverse relationship Fig. 5.

Fig. 5
figure 5

SEM image of AuNPs/PS synthesized by laser ablation a 532 nm, b 1064 nm laser wavelength

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The J–V characteristics of AuNPs/PS/n-Si occur in Fig. 6 in dark circumstances with a current density of 20 mA/cm2, an etched time of 18 min, and an HF of 16%. At laser energies of 600, 800, and 1000 mJ, it appears the current rises with the presence of AuNPs on the PS layer. Because of high electrical conductivity of the AuNPs, current increases with compared to the PS sample and decreases in contrast to bulk Si due to the high degree of crystallized form.

Fig. 6
figure 6

J–V characteristic under the dark of bulk Si, PS and AuNPs/PS with various laser pulse energies a 532 nm, b 1064 nm laser wavelength

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The streaming recombination current is not uniformly spread through the structure, as seen Fig. 7 by the comparison log (J) with bias voltage of AuNPs porous silicon usually at local area. The ideal factor and barrier height ΦBn calculated according to Eqs. (3) and (4) because electrons do not have enough energy to cross the barrier height, there is a lot of recombination between excited electrons and holes. The most recent is known as diffusion current, which occurs at higher voltages and results in an exponential rise in output current [63].

$$\Phi_{{{\text{Bn}}}} = \frac{{K_{{\text{B}}} T}}{q}\ln \left( {\frac{{A^{**} T^{2} }}{J}} \right)$$
(3)
$$n = \frac{q}{{K_{{\text{B}}} T}}\frac{d\upsilon }{{d(\ln \,J)}}$$
(4)

J, forward current density (μA/cm2), kB, Boltzmann constant (1.38 × 10−23 J/K), V, the applied voltage, A**, represents the value of Richardson’s constant (112 A/cm2 K).

Fig. 7
figure 7

log(J) with bias voltage of c-Si, PS and AuNPs Porous silicon at various laser energies, 500 pulses and laser wavelength (a) 532 nm, (b) 1064 nm on PS substrate under dark

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Ideality factor (n) calculated heterojunctions have barrier heights (Bn) between (0.60 and 0.62) eV in 532 nm and increasing from 0.64 to 0.679 eV in 1064 nm. These values range from 1. 2 to 2.2 for 532 nm and from 1.1 to 1.8 for 1064 nm. Applied low applied voltage to the saturation current density is obtained from the linear region of the semi-log forward I–V curves (Js) (Table 4).

Table 4 Value of saturation current, ideality factor, and barrier height of c-Si, PS and AuNPs/PS samples at various laser energies, etching time 18 min with varied laser wavelength
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Figure 8 demonstrates the sandwich structure with a reverse bias voltage and some light. When PS is coated with Au film using various wavelengths of laser deposition, photocurrent increases (532 and 1064 nm). By shining light on the junctions additionally, the reverse bias current was improved, which is anticipated of the formation of electron–hole pairs in the zone of energy depletion of the incoming photons exceeds the sandwich structure's smallest immediate band gap. Conclusions of the previous studies clearly reveal that these sandwich arrangements possess a good light response, making it a better material for optoelectronic device fabrication.

Fig. 8
figure 8

Jph–V curve of AuNPs/PS n-type substrate when light with varied laser wavelength (a) 532 nm, (b) 1064 nm

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Figure 9 shows the spectra of AuNPs divided two distinct portions the first shows responsiveness as a result of the near infrared ~ 600 nm wavelength region of Au nanoparticle absorption. Responsivity, the second section, shows how the PS layer absorbs visible light 850 nm. These findings enhanced the compatibility of Au with PS structures, enhancing the performance of porous silicon. The responsivity is calculated by using Eq. (5)

$$R_{\lambda } = \frac{{I_{{{\text{ph}}}} }}{{P_{{{\text{in}}}} }}$$
(5)

Iph, current of the optical container, Pin, input power, Spectral responsivity Rλ is the detector signal.

Fig. 9
figure 9

Responsivity of AuNPs produced on PS substrate with varied laser wavelength (a) 532 nm, (b) 1064 nm

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Figure 10 demonstrates measurement of detectivity D* at various wavelengths nm, to altered wavelength laser deposition 532 nm, and 1064 nm. The highest values are around (0.39260385, 0.497405712, and 0.945842868) (cm Hz1/2/W) × 1012, which increase with increasing energies 600, 800, 1000 mJ in wavelength 532 nm, and (0.815409152, 0.85192001, and 0.973185088) in wavelength 1064, which match to visible energies of (532, 1064) nm, including both. Calculated detectability by Eq. (6) [64, 65].

$$D^{*} = \frac{{\sqrt {S_{{{\text{det}}}} \Delta f} }}{NEP}$$
(6)

The detector active area (Sdet), which represents the noise equivalent power, and detectivity (D*), which reflects the response of the frequency.

Fig. 10
figure 10

Detectivity of AuNPs produced on PS substrate with varied laser wavelength (a) 532 nm, (b) 1064 nm

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The link between the quantum effectiveness of the device and the wavelength of the incident light is depicted in Fig. 11. Quantum efficiency increased as the band gap of the structure widened. It was high at the time because quantum efficiency is proportional to R. Maximum quantum efficiency is determined to be 29.9% in 600 mJ, 49.7% in 800 mJ, and 94.5 in 1000 mJ at wavelength 800 nm and (66.7%, 85.1%, 95.6%) in 1064 nm crystal (600, 800, 1000 mJ). The spectral responsiveness and the quantum efficiency are determined by Eq. (7) [66,67,68].

$$\eta = \frac{h\upsilon }{q}R_{\lambda }$$
(7)
Fig. 11
figure 11

Quantum efficiency of AuNPs produced on PS substrate with varied laser wavelength (a) 532 nm, (b) 1064 nm

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As the bandgap of the structure grew larger, the quantum efficiency improved. The highest efficiency was 95.6%when separate lasers, 532 nm and 1064 nm, were used to deposition thin layer. The efficiency increased with energy gap dropped, laser deposition wavelengths expanded. The quantum efficiency of relationships inside a system determines it.

Conclusion

The pore size of porous silicon (PS) films increases as the laser wavelength decreases; from the (J–V) characteristic, it is evident that the current increased when AuNPs were present. At laser energy of 600, 800, and 1000 mJ ablated on the PS layer. This is caused by the AuNPs high conductivity of the layer, this due to the current rise in comparison the PS sample and decrease in comparison with bulk Si. When employing PS layer instead of c-Si, the responsibility has improved, and it has improved even more after doping the AuNPs. The Au-NPs can be deposited on the PS surface to assist improve light absorption, reduce resistance, and improve overall conversion efficiency. These findings show that a low-cost visible photodetector based on this high-quality photodiode could be a feasible option in commercial photoelectric applications.