Introduction

Nanotechnology plays a critical role in the fabrication and enhancement of products in science and technology. In particular, it is capable of producing an ultra-high-quality structure with controllable properties at the desired morphology, size and shape.1,2,3,4,5 For instance, thin-film technology, such as epitaxial growth, electrochemical deposition, spin coating, thermal evaporation and magnetron sputtering, is an important and widely used technique for the fabrication of more effective photodiodes and photovoltaic devices.6,7,8,9,10,11,12,13,14 Among these techniques, magnetron sputtering enables co-deposition of materials by superior control of purity, film thickness and surface morphology.

There is high demand for organic and inorganic materials in applications such as photonics and flexible electronics.15,16,17 Among these materials, transparent metal oxides have been widely used in optoelectronic devices due to their unique optical and electrical properties. Whilst ZnO, TiO2, CdO, SiC and NiO may be preferred for many optoelectronic applications,18,19,20,21,22 tungsten oxides have garnered a great deal of interest due to their unique properties in applications ranging from electro-chromatic,23 sensor24,25 and high-quality interconnections,26 to optoelectronic, photovoltaic and energy storage devices, and its products can be altered by several techniques during the deposition process.27 Additionally, metal oxide features can be modified by doping or tuning the chemical composition by another element.8,28 For instance, germanium (Ge) has been used as a dopant in metal oxides to improve their performance in various applications.15,28,29,30,31,32 Additionally, some studies have reported the use of tungsten as a dopant material—for example, W doped to TiO2,33 BaSrTiO334 and SnO2 to improve the structural, optical, electrical and photocatalytic performance. Other examples of the use of W as a dopant can also be found; for instance, W is doped to VO235 to reduce to the critical temperature for metal–insulator transition. The geometric and electronic properties of the W-doped Ge cluster were investigated by density functional theory. It was found that W-Ge and their oxides can be used as dopants, semiconductor or insulator layers, or also doped to another in optoelectronic applications.

Hence, an Al/Si/WOx:Ge(5.7%)/Ag heterojunction was fabricated by doping Ge into tungsten oxide by the co-deposition technique under a vacuum environment. Structural and morphological investigations were performed, and the I–V characteristic curve was determined under dark and various light intensities to provide an alternative for optoelectronic circuit elements.

Materials and Methods

The physical vapour deposition (PVD) technique was employed for the fabrication of a heterojunction diode, as shown in the structural diagram in Fig. 1. Firstly, a p-type Si substrate with an Al support layer was cleaned using acetone, methanol and distilled water, respectively, in an ultrasonic bath and then dried with nitrogen gas. Afterwards, a Nanovak magnetron sputtering system (Model: NVTS-400) which has two RF and one DC magnetron sputter head, was used to deposit Ge-doped WOx thin film by the co-deposition technique. The base pressure of the deposition system was approximate 0.133 kPa during the deposition and was about 0.266 kPa under a 0.666 kPa Ar gas environment. Applied power and Ar pressure are generally used to alter the deposition rate of target materials so the film thickness and doping material ratio can be controlled during the co-deposition process. The deposition rate of sputtered materials was controlled by a quartz crystal thickness monitor. Hence, the deposition rate of the W target with a purity of 99.99% percent was kept at 1.6 Å s−1 by applying DC voltage (395 V, 250 mA). Besides this, an RF power-supply-connected magnetron sputter source was used for the co-deposition of Ge (99.99% percent purity) with a deposition of 1.2 Å s−1 by applying 55 W sputtering power. The co-deposition process was carried out up to reach desired thickness. Fabrication of the heterojunction was finally completed by deposition of Ag Schottky contacts by RF magnetron sputtering with a deposition rate of 1.8 Å s−1. The thickness of the Ag contact was settled at approximately 150 nm.

Fig. 1
figure 1

Structural diagram of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction.

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The phase structure of the heterojunction was examined by x-ray diffraction (XRD) (G.N.R. Europe 600 diffractometer) using Cu-Kα (1.5418740 Å) radiation from 10 \(^\circ \) to 80 \(^\circ \). Scanning electron microscopy (SEM) (FEI Versa 3D DualBeam) was employed to examine the surface morphology of the deposited film. Energy-dispersive x-ray spectrometry (EDX) was performed to determine the elemental composition of the heterojunction. Additionally, the doping ratio of Ge in thin film was obtained from SEM–EDX analysis. The deposited film thickness was also determined from a cross-section SEM image of the fabricated device.

I–V characteristic measurement of the heterojunction was carried out using the FYTRONIX Solar Simulator LS 900 Characterisation System, which is fully automated and controlled by a computer and enables dark and various light I–V characterisation.

Results and Discussion

Phase Structure, Surface Morphology and Elemental Composition

The XRD graph of Ge-doped WOx thin film is illustrated in Fig. 2a, and the high-magnification XRD spectrum of the low-intensity region (labelled in Fig. 2a) is demonstrated in Fig. 2b. The amorphous to polycrystalline phase structure of the thin film is clearly seen in Fig. 2a and b, and the Ge-doped WOx thin film has obvious phase peaks which can be assigned to Ge0.04WO3, GeO2, WO3 and W5O14 phases, for which the standard spectrums are shown in Fig. 2c. Also, details of the crystal parameters of these phases are given in Table I.

Fig. 2
figure 2

(a) The phase structure of Ge-doped WOx thin film, (b) high magnification XRD spectrum of the selected area of Fig. 2(a), (c) standard XRD spectrum.

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Table I Crystal parameters of detected phases from XRD measurement
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The structural parameters including particle size (D), dislocation density (\(\delta \)) and lattice strain (\(\varepsilon \)) were calculated from the most dominant (sharp) peaks in the spectrum and are given in Table II. The particle size is calculated by the Scherrer equation, \(D=0.90\lambda /\beta cos\theta \), where \(\lambda \) is the wavelength of the incident x-rays (1.5418740 Å for Cu-Kα), \(\beta \) is the full width at half maximum (FWHM) and \(\theta \) is the Bragg angle. The dislocation density is calculated with the Williamson and Smallman formula as \(\delta =1/{D}^{2}\) and the equation \(\upvarepsilon =\beta \mathrm{cos}\theta /4\) is used to obtain lattice strain. The low dislocation density and lattice strain and large particle size indicates that the film structure is properly crystallised.36,37

Table II Structural parameters of phases that occur in the thin film layer
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The surface morphology of Ge-doped WOx thin film deposited on a p-type Si wafer by PVD was investigated by SEM, and the SEM images are illustrated in Fig. 3a. The PVD technique leads to a uniform surface profile with some visible grain boundaries. The thin film has a smooth surface without cracks or pores, as shown in Fig. 3a. As illustrated in Fig. 3b, heterojunction layers are distinguishable and film thickness was measured as 435 nm from the cross-section SEM image.

Fig. 3
figure 3

(a) SEM image of Ge-doped WOx thin film surface, (b) represents the cross-section SEM image of the heterojunction.

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SEM–EDX mapping was employed to characterise the chemical composition of the deposited film. Figure 4d indicates that the thin film contains elements of W, Ge and O. In Fig. 4a–c, it can be clearly seen that all the W, Ge and O are homogeneously distributed. The percentage atomic content is 71.75% W, 11.24% Ge and 17.01% O, and the percentage of elemental weight is demonstrated in the inset of Fig. 4d. It is clear that W and Ge have 92.5% and 5.7% elemental weight in the deposited film. Additionally, the EDX spectrum indicates that the film has 1.9% wt O. Since the deposited thin film has contacted the atmosphere, the oxidation process has taken place naturally. The results of the EDX analysis support the results of the XRD analysis. Hence, the heterojunction will be labelled Al/Si/WOx:Ge(5.7%)/Ag.

Fig. 4
figure 4

SEM–EDX elemental mapping of (a) tungsten, (b) germanium, (c) oxygen and (d) EDX spectrum of the thin film surface.

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Electrical Characterisation

In this work, 5.7% Ge-doped WOx thin film was deposited on a p-type Si wafer by PVD technique and afterwards Ag Schottky contacts were grown on the film surface. The synthesised heterojunction actually formed as a metal–insulator–semiconductor (MIS) type Schottky barrier diode (SBD) structure. Since the thin film deposited on the semiconductor layer (p-type Si) formed as a metal oxide (supported by XRD and EDX analyses), the metal contacts were taken and formed the MIS structure. Here, the metal oxide layer is considered an insulating layer, and similar studies are available in the literature.38,39,40,41 The I–V characteristics of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction were investigated under dark and various illumination intensities ranging from 20 mW cm−2 to 100 mW cm−2 between ± 2 V applied voltage ranges at room temperature. Based on the current–voltage mechanism of the metal–insulator–semiconductor Schottky barrier diode, electrical characteristics of the diode including diode ideality factor, barrier height and series resistance can be calculated by different methods.42,43

In the conventional method, the relationship between the current and voltage is determined by thermionic emission theory with the following equation44,45,46:

$$I=A{A}^{*}{T}^{2}\mathrm{exp}\left(-\frac{q{\varnothing }_{b}}{\mathrm{kT}}\right)[\mathrm{exp}\left(\frac{q(V-{\mathrm{IR}}_{s}}{\mathrm{kT}}\right)-1]$$
(1)

where A is the active diode area, A* is the Richardson constant (32 A cm−1 K2 for p-type Si), q is the electron charge, ϕb is the barrier height, k is the constant, T is the temperature (Kelvin), V is the applied voltage and Rs is the series resistance. In the case of \(V-{\mathrm{IR}}_{s}>>3\mathrm{kT}\) Eq. 1 is formed as in Eq. 2

$$I={I}_{0}\mathrm{exp}\left(\frac{\mathrm{qV}}{\mathrm{nkT}}\right)$$
(2)

where

$${I}_{0}=A{A}^{*}{T}^{2}\mathrm{exp}\left(-\frac{q{\varnothing }_{b}}{\mathrm{kT}}\right)$$
(3)

After taking the logarithm of both sides of Eq. 2 and the derivative concerning V, the diode ideality factor (n) can be given by

$$n=\frac{q}{\mathrm{kT}}\frac{dV}{d\mathrm{ln}\left(I\right)}$$
(4)

The ideality factor (n) can be calculated from the slope of the linear region of the ln(I) versus V graph. Additionally, the reverse saturation current (I0) is derived from the point where the linear region of the graph of ln(I) versus V intersects ln(I). After defining the I0, the barrier height is calculated using Eq. 5.

$${\phi }_{b}=\frac{kT}{q}\mathrm{ln}(\frac{A{A}^{*}{T}^{2}}{{I}_{0}})$$
(5)

The Cheung–Cheung method is the second method used to determine the ideality factor, barrier height and series resistance, using the Cheung–Cheung functions47 which are given by the following equations:

$$\frac{dV}{\mathrm{dln}(I)}={\mathrm{IR}}_{s}+\frac{\mathrm{nkT}}{q}$$
(6)
$$H\left(I\right)=V-\frac{\mathrm{nkT}}{q}\mathrm{ln}(\frac{I}{A{A}^{*}{T}^{2}})$$
(7)
$$H\left(I\right)=I{R}_{s}+n{\varnothing }_{b}$$
(8)

By considering the low and medium bias region of the I–V plot, the \(\frac{dV}{\mathrm{dln}(I)}\) versus I and H(I) versus I graphs are plotted. And from the slope of the \(\frac{dV}{\mathrm{dln}(I)}\) versus I graph and the value where the curve cuts the y-axis using other constants, Rs and n are calculated, respectively. In addition, it is possible to determine the ϕb by using the point where the curve comes from the H(I) versus I graph, cutting the y-axis and the n value. Also, the slope of this curve can be used to define the Rs value. Furthermore, from the graph of junction resistance (\(\mathrm{Rj}=\frac{\partial V}{\partial I}\)) versus V, the series resistance Rs of the junctions can be determined.48,49

Figure 5 illustrates the I–V characteristic curve of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction, and it can be clearly seen that the heterojunction shows rectifying characteristics and its photoconductivity increases with the increase in the intensity of light falling on it. Semi-logarithmic I–V characteristics of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction are demonstrated in Fig. 6, and asymmetry can be observed between the reverse and forward bias voltages, especially in the dark region. In addition, it is seen that the linear region of the curves drops between 0.05 and 0.3 V under forward bias and the series resistance effect appears, while voltage increases from this value. At the same time, non-saturation behaviour can be observed under reverse bias, and this can be explained primarily by the interface states of the WOx:Ge(5.7%) layer and metal, and image-force lowering by the barrier height.50 Photons with higher energy than the forbidden band gap energy under illumination provide the formation of new electron–hole pairs in the depletion region of the semiconductor. The structure is stressed under the external electric field, and the electron–hole pairs generated are forced to separate by a strong internal electric field at the grain boundary. And thanks to the electric field, electrons are quickly swept away and photoconductivity is increased. Hence, the photoconductivity becomes more distinguishable in the range of 1 V to 2 V.

Fig. 5
figure 5

I–V characteristic curve of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction.

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Fig. 6
figure 6

Semi-logarithmic I–V characteristic curve of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction.

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In Fig. 7, ln(I) versus ln(V) is plotted to illustrate in greater detail the current conduction mechanism of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction in the forward bias region. It is clear that three regions are available under both dark and light intensity as illustrated in Fig. 7. The region where the ln(V) value is between −2.5 and −1.5 falls into the ohmic region of the first region. This is because the amount of current produced in the heterojunction is greater than the current generated by the injected free carriers.51,52,53,54 The region with ln(V) values between −1.5 and 1 is the second region, and it refers to the space-charge-limited current (SCLC) region controlled by traps. The reason for these traps is the increased injection of electrons from the metal to the film with increasing applied voltage. The increase in the number of injected electrons leads to the filling of the traps and increases the space charges.55,56,57 The third region occurs at a high bias region and has a strong injection area. In this region, electrons escape from traps and contribute to the SCLC.44,55,58,59

Fig. 7
figure 7

Double logarithmic plots of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction.

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Figure 8 presents the Rj–V graph of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction under the forward bias condition. It is evident that junction resistance is high at low voltage, and with higher voltage, it decreases. Additionally, the increase in the current depending on the carrier concentration with the increase in light intensity leads to a drop in the junction resistance. It is seen that the Rj values fluctuate and decrease with increasing applied potential. This can be attributed to the disordered charge distribution.

Fig. 8
figure 8

Forward bias Rj–V graph of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction.

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Figure 9 shows changes in the series resistance values calculated from the curves of Rj–V, d(V)/dln(I)–I and H(I)–I, depending on light intensity. It is obvious that all Rs values calculated with the three methods decreased exponentially with the increasing intensity of light. Rs values are determined as 1.23 × 103 Ω, 1.05 × 105 Ω and 1.5 × 105 Ω from the Rj–V, d(V)/dln(I)–I and H(I)–I curves under dark conditions, respectively. Also, under 100 mW cm−2 illumination, these Rs values drop to 1.15 × 102 Ω, 4.29 × 102 Ω and 5.29 × 102 Ω, respectively. The reason for the decrease in Rs values with increasing light intensity is related to increasing photoconductivity.

Fig. 9
figure 9

The relationship of evaluated Rs values with different methods against the light intensity. Inset represents the high magnification graph of Rs values calculated with the Rj–V curve.

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n and ϕb , depending on the light intensity, were calculated and are respectively presented in Fig. 10a and b. Values of n and ϕb calculated by both methods show similar behaviour against the change in light intensity. While n values determined from the d(V)/dln(I)–I curve are between 2.79 and 1.70, the H(I)–I curve yielded ϕb values between 1.07 eV and 0.67 eV. Additionally, n and ϕb values obtained from ln(I)–V curves take values between 5.69 and 4.16, and 0.73 eV and 0.56 eV, respectively. The n and ϕb values have an opposite correlation, as shown in Fig. 10a and b. Both barrier height and ideality factor values are coherent with those in the literature. Kocyigit et al. reported a similar finding regarding the relationship between ϕb and n.60 Additionally, n values calculated by both methods are far from ideal diode values (n = 1). The reasons for this are the potential drop across the interface layer, natural oxide layer formation, and the overcurrent at the interface state which is between the series resistance and Al/Si/WOx:Ge(5.7%)/Ag layers.48,61 Another reason for the high n value could be the non-homogeneous distribution of charges at the interface layer.62 The n values showed a fluctuating change with the increase in light intensity. This can be explained by the rearrangement and reconstruction of the structure at the molecular level by increasing the light intensity.

Fig. 10
figure 10

(a) Diode ideality factor, (b) barrier height of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction against the intensity of light.

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In Fig. 11 the graph of the reverse saturation current, I0, versus light intensity is presented. It is obvious that the reverse saturation current increases with light intensity and reaches its maximum value at 80 mW cm−2 and then drops again. The reason for this trend is that photo-generated carriers of light activate recombination at the interface. While the I0 value in a dark environment is 7.31 × 10–8 A, it increases to 4.69 × 10–5 A at 80 mW cm−2 illumination. It is remarkably clear that reverse saturation current increases approximately 1000-fold, and it means that the designed heterojunction is highly sensitive to light. The increase in I0 with light intensity can be attributed to a decrease in the value of Rs.

Fig. 11
figure 11

The plot of reverse saturation current versus light intensity.

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The rectification ratio (r) is a vital parameter for rectifier diodes and is calculated by the formula \(r={I}_{f}/{I}_{r}\).63,64 Here, If and Ir refer to currents under forward bias and reverse bias, respectively. r values were calculated at voltage of 0.5 V, 1 V, 1.5 V and 2 V under different light intensity, and the results are presented in Fig. 12. It is clear that r values at certain voltages decrease exponentially with increasing light intensity, which is in agreement with the literature.65,66 The highest r value under dark conditions was observed at a voltage of 1.5 V, and there is no obvious trend between r value and applied bias voltage.

Fig. 12
figure 12

Rectification ratio (r) of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction plotted as a function of light intensity at certain bias voltages.

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In Fig. 13a–d, the changes in photocurrent (Iph) depending on light intensity are evaluated at certain voltages (0.5 V, 1 V, 1.5 V and 2 V) under forward and reverse bias. It is observed that the photocurrent increases proportionately with the light intensity under forward bias conditions, while this increase reaches a peak point at 80 mW cm−2 under reverse bias. This can be explained by the radial change in intensity which alters the photoabsorption.66 Furthermore, it is seen that Iph increases with increasing bias voltage, and the Iph under forward bias is higher than the Iph under reverse bias at all illuminations, which promotes the nature of the photodiode.

Fig. 13
figure 13

The plot of photocurrent (Iph) under (a)  ± 0.5 V, (b)  ± 1 V, (c)  ± 1.5 V, (d)  ± 2 V against light intensity.

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The photoresponsivity (R) value of the fabricated diodes can be calculated with a following equation:

$$R=\frac{{I}_{\mathrm{ill}}-{I}_{\mathrm{dark}}}{{P}_{\mathrm{inc}}.A}$$
(9)

where Iill is the current under illuminated conditions, Idark refers to the dark current, Pinc is the incident light power and A is the contact area of the diode (A = 7.85 × 10−7 m2). The photoresponsivity plots of the fabricated Al/Si/WOx:Ge(5.7%)/Ag heterojunction at certain bias voltage values (± 0.5, ± 1, ± 1.5 ve ± 2 V) against illumination intensity are given in Fig. 14a–d. For each bias voltage value, forward responsivity (Rf) and reverse responsivity (Rr) are presented together using two y-axes. It is clear that Rf and Rr are enhanced with illumination intensity and that Rf values are higher than Rr values at all voltage values. In addition, R values rise with increasing bias voltage under both forward and reverse bias.

Fig. 14
figure 14

Photoresponsivity versus light intensity plot of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction at (a)  ± 0.5 V, (b)  ± 1 V, (c)  ± 1.5 V, (d)  ± 2 V.

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The photosensitivity (S) of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction at voltages of ± 0.5, ± 1, ± 1.5 ve ± 2 V was determined by the following relation67:

$$S=R\frac{T}{V}$$
(10)

where S, R, T and V refer to the photosensitivity, photoresponsivity, thickness of the active layer (435 nm for Ge-doped WOx layer) and applied voltage, respectively. Figure 15a–d illustrates the photosensitivity curves at certain forward and reverse voltage values against the light intensity. Similar to Fig. 14, for each bias voltage value, forward sensitivity (Sf) and reverse sensitivity (Sr) are plotted together by using double y-axes. The similarity of the photosensitivity and photoresponsivity response of the fabricated diode is notable, since photosensitivity increases with increasing light intensity and applied voltage.

Fig. 15
figure 15

Photoconductivity sensitivity versus light intensity plot of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction at (a)  ± 0.5 V, (b)  ± 1 V, (c)  ± 1.5 V, (d)  ± 2 V.

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Figures 16 and 17 demonstrate the photovoltaic and photodiode region and the photovoltaic parameters (\(\mathrm{Impp}\), \(\mathrm{Isc}\), \(\mathrm{Vmpp}\), \(\mathrm{Voc}\) ve FF) of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction under several light intensity values, respectively. The fill factor was calculated with Eq. 11, given by:

$$\mathrm{FF}=\frac{\mathrm{Impp} \times \mathrm{Vmpp}}{\mathrm{Isc} \times \mathrm{Voc}}$$
(11)

where \(\mathrm{Impp}\) is the maximum power point current, \(\mathrm{Vmpp}\) is the maximum power point voltage, \(\mathrm{Isc}\) and \(\mathrm{Voc}\) refers to the short-circuit current and open-circuit voltage, respectively.

Fig. 16
figure 16

The plot of the photovoltaic region of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction under several light intensities.

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Fig. 17
figure 17

Changes in the photovoltaic parameters (a) \(\mathrm{Impp}\), (b) \(\mathrm{Isc}\), (c) \(\mathrm{Vmpp}\), (d) \(\mathrm{Voc}\) and (e) FF against several light intensity values.

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The photovoltaic parameters of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction were determined, and their variation against light intensity is illustrated in Fig. 17a–e. The calculated FF values are obtained between 0.2668 and 0.2392. It is also seen that FF values gradually fluctuate between 20 mW cm−2 and 60 mW cm−2, decrease to a minimum value at 80 mW cm−2 and reach a maximum value at 100 mW cm−2. \(\mathrm{Voc}\) and \(\mathrm{Vmpp}\) are between 0.0336 V and 0.047 V, and 0.0184 V and 0.0253 V, respectively, and they increase with light intensity. \(Isc\) values between −5.1178 × 10−5 A and − 3.6252 × 10−5 A and Impp values between −2.4129 × 10−5 A and −1.6753 × 10−5 A have similar trends as FF values. As the values of \(\mathrm{Isc}\) and \(\mathrm{Impp}\) are in the negative region, their values increase between 20 mW cm−2 and 60 mW cm−2, and they decrease to the minimum value at 80 mW cm−2 and increase at 100 mW cm−2.

Conclusion

A Ge-doped WOx layer was successfully deposited on a p-type Si substrate by a PVD method to fabricate an Al/Si/WOx:Ge(5.7%)/Ag heterojunction. XRD results indicate that the active layer has an amorphous and polycrystalline structure with the crystal phase of Ge0.04WO3, GeO2, WO3 and W5O14. The thickness of the active layer was observed as 435 nm from the cross-sectional SEM image. Additionally, the SEM–EDX mapping image shows that W, Ge and O are homogeneously distributed on Si wafers, with molecular weight percentage of 92.5%, 5.7% and 1.9%, respectively. In order to investigate the electrical features of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction, Ag-rectifying contacts were grown on film surfaces. The electrical properties of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction were characterised under dark and various light intensities at a ± 2 V voltage difference. Diode parameters (n, ϕb, Rs andI0) were determined under dark and illumination conditions using different methods. Whilst, in general, I0 values increase with the increase in light intensity, ϕb and Rs values decrease. n values show fluctuation with light intensity. At the same time, Iph, R and S values of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction were investigated depending on the light intensity under forward and reverse bias. Generally, these values increase with the increase in light intensity. Additionally, the photovoltaic parameters (\(\mathrm{Impp}\), \(\mathrm{Isc}\), \(\mathrm{Vmpp}\), \(\mathrm{Voc}\) ve FF) of the Al/Si/WOx:Ge(5.7%)/Ag heterojunction depending on light intensity were investigated, and an increase in the FF value with increasing light intensity was observed. In light of these results, it can be concluded that the fabricated heterojunction has photodiode and photovoltaic properties.