Novel photoconductive Ag/nanostructure ruthenium oxide/p-type silicon Schottky barrier diode by sol–gel method

J Sol-Gel Sci Technol (2013) 67:368–375 DOI 10.1007/s10971-013-3090-x

ORIGINAL PAPER

Novel photoconductive Ag/nanostructure ruthenium oxide/p-type silicon Schottky barrier diode by sol–gel method Ahmed A. Al-Ghamdi • Attieh A. Al-Ghamdi • Omar A. Al-Hartomy • Ahmed M. Nawar • E. El-Gazzar • Farid El-Tantawy • F. Yakuphanoglu

Received: 27 April 2013 / Accepted: 8 June 2013 / Published online: 22 June 2013 Ó Springer Science+Business Media New York 2013

Abstract A new Schottky photodiode of Ag/RuO2/p-Si/ Al was successfully fabricated using spin-coating technique. The ruthenium oxide (RuO2) nanoparticles with an average size of 8 nm were synthesized using a sol–gel method. The crystal structure and morphology of the synthesized RuO2 were analyzed by means of X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy and selective area electron diffraction. The rectification ratio of the diode was found to be 112 at ±2 V. The ideality factor and barrier height values of the Ag/RuO2/p-Si/Al diode were obtained to be 1.47 and 0.55 eV, respectively. The Cheung–Cheung and Norde’s models were used to determine the diode parameters. The photoresponse behavior of the fabricated Ag/RuO2/p-Si/Al diode was studied under various illumination intensities. The transient photocurrent results indicate that photocurrent under illumination is higher than the dark current and

A. A. Al-Ghamdi  O. A. Al-Hartomy  F. Yakuphanoglu Department of Physics, Faculty of Sciences, King Abdulaziz University, Jeddah, Saudi Arabia A. A. Al-Ghamdi Department of Physics, Faculty of Science, King Abdulaziz University, North Campus, Jeddah, Saudi Arabia O. A. Al-Hartomy Department of Physics, Faculty of Science, Tabuk University, Tabuk 71491, Saudi Arabia A. M. Nawar  E. El-Gazzar  F. El-Tantawy Department of Physics, Faculty of Science, Suez Canal University, Ismailia, Egypt F. Yakuphanoglu (&) Department of Physics, Faculty of Science, Firat University, 23119 Elazig, Turkey e-mail: [email protected]; [email protected]

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this indicates that the fabricated diode behaves as a photodiode. The capacitance–voltage–frequency measurements indicate that the capacitance of the diode depends on voltage and frequency. The obtained results suggest that the new Ag/RuO2/p-Si/Al diode can be used an optical switching device for optical sensor applications and are also expected to be generated in the future study. Keywords Ruthenium oxide nanoparticles  Schottky photodiode  Sol–gel

1 Introduction This study is part of an on-going research project aiming to develop high performance nanostructure metal oxides for photodiode with high efficiency and good stability. Nanoscale materials, due to their diverse electronic and optical properties, and with a range of architectures, are constantly being explored for an array of low-cost, sensitive, and scalable photodetection technologies [1–3]. Alternative low-loss materials, such as conducting oxide films, are potentially advantageous for many plasmonic applications, since they exhibit both a small negative real permittivity and relatively small losses in the near infrared [4–7]. In fact, conducting oxide materials have much lower free charge carrier concentrations (1020-22 cm-3) as compared to metals ([1023 cm-3) [8, 9]. This makes their plasma frequencies smaller and hence their imaginary permittivity and losses lower than those of metals, making them suitable for transformation optics such as photodetectors [10, 11]. In particular, ruthenium oxide is considered one of the most important metal-oxides because of its high reactivity with reducing agents due to its oxidizing properties, low resistivity (*35 lX cm at room temperature), good thermal

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stability and high resistance to chemical corrosion and so on [7–10]. These desirable characteristics have attracted attention for its application in diverse fields both in the electronics and chemical industry such as catalyst, electrode in electrochemical process, inter diffusion barrier, precision resistor element, contact electrode material in ferroelectric random access memory devices that offers superior polarization fatigue properties with very low leakage current, cryogenic devices, temperature sensor, magnetoresistance sensor and others [12–16]. Semiconducting-metal Schottky barrier fabrication and the subsequent extraction of the contact parameters is an attractive research field for realization of electronic and photovoltaic devices [17–20]. Harvesting aforementioned benefits, and to the best of the authors knowledge, RuO2 nanostructures for Schottky photodiode are still unavailable in literatures. The target of the study is the fabrication of a novel Schottky photodiode based on Ag/RuO2/p-Si/Al nanoparticles. The microstructure of the synthesized RuO2 nanoparticles was examined in details. Moreover, the DC and AC electrical properties of the fabricated RuO2/Si-p Schottky contact in dark conditions were tested. Finally, the photoresponse of as prepared Ag/ RuO2/p-Si/Al devices under different illuminating power were examined, too.

2 Experimental part 2.1 Synthesis of ruthenium oxide nanoparticles Ruthenium chloride, isopropanol and diethanolamine (DEA) were used as starting material, solvent and stabilizer, respectively without further purification. First, ruthenium chloride was dissolved in isopropanol and then DEA was slowly added under magnetic stirring to prepare a solution of 0.5 M. The resulting mixture was stirred for 3 h at 60 °C to yield a clear and homogeneous solution. Then the solution was aged for 48 h at room temperature, which served as the coating solution. Thin films of RuO2 were prepared by spin coating of the respective coating solutions onto pre-cleaned p-type silicon substrates at rotation speed of 4,000 rpm for 30 s in ambient condition. Afterwards, the films were dried at 300 °C for 30 min in air to evaporate the solvent and organic residues. 2.2 Fabrication of Ag/RuO2/p-Si/Al diode The RuO2/p-Si junction was fabricated by spin coating technique. For this, the RuO2 film was thermo-cleaned at 200 °C for 5 min under Ar atmosphere. RuO2-Gel was deposited on the p-Si (100) wafer and glass substrates by spin coating technique and then, it was dried at 150 °C for 10 min and annealed at 400 °C for 1 h, prior to growth. The thickness

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of the p-Si wafer was 800 lm with resistivity of 20–30 Xm. Before fabrication of the Schottky junction the silicon wafer was cleaned using HF to remove the native oxide layer and deionized water. Finally, silicon wafer was cleaned according to method based on successive baths of methanol and acetone [1–3]. Before deposition of the RuO2 layer, the ohmic contact was deposited by evaporating Al metal on the back of Si wafers followed by annealing at 570 °C for 5 min in nitrogen atmosphere. The top Ag contacts were deposited by evaporating Ag metal onto RuO2 film. The contact area of the diode was calculated to be 0.32 cm2. 2.3 Characterization technique The crystallinity and phase purity of the synthesized RuO2 were investigated by X-ray diffraction pattern using a Philips (PW1130) X-ray diffractometer with CuKa radiation (k = 0.1541 nm). The chemical composition of the synthesized RuO2 was analyzed by an energy dispersive spectroscopy unit (EDS) (FESEM; JEOL-JSM-7600F). Transmission electron microscopy (TEM) measurements were performed on a (TEM; JEM-2100F) at an acceleration voltage of 130 kV contained the selected area electron diffraction (SAED) pattern (nickel grid with mesh size, 300 mesh 9 80 lm) and the thickness of the sample about 0.5 lm. The electrical characterization of the fabricated diode was performed using a programmable system (Keithley 6517b). In the frequency range 42 Hz–1 MHz, a computerized HIOKI 3531-Hi-tester LCR meter was used to measure, directly, the impedance (Z), loss tangent (tand) conductance (G) and capacitance (C). Photovoltage measurements were executed using a 200 W halogen lamp. The light intensity of the lamp was controlled by change of the current across the lamp and the intensity of light was measured using a solar power meter (TM-206).

3 Results and discussion Figure 1a shows X-ray diffraction pattern of the RuO2 film prepared by sol–gel technique. All the reflections peaks were assigned to a typical RuO2 phase (JCPDS 43-1027). RuO2 in a tetragonal crystallographic structure and no presence of Ru in a metallic form was found [21, 22]. It can be concluded that the poor constructive diffractions are probably due to the nanocrystalline nature and the presence of defects (such as surface hydroxyl group) of hydrous RuO2 [23, 24]. The crystallite size of the ruthenium oxide (D) was determined using Scherrer equation [4]: D ¼ 0:9k=b cos h

ð1Þ

where k is the X-ray wavelength, h is the Bragg diffraction angle and b is the full width at half maximum (FWHM) of the

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Annealed Ruo2 ThinFilm at 400 °C

(a)

Simulated

10

20

30

40

50

60

(301)

(310)

(200)

(211) (200)

(101)

(110)

Intensity, (Counts/s)

diffraction peak. The average size of the RuO2 particles was found to be about 8 nm. The lattice parameters of RuO2 were calculated using the Topas P-2 software attached on the X-ray and were found to be a = 0.4491 nm and c = 0.3105 nm. The typical EDS spectrum of the synthesized RuO2 is shown in Fig. 1b. It is clear that the synthesized RuO2 is formed from ruthenium and oxygen, only. The concentration of Ru is 65 at.%, whereas oxygen is 35 at.%. Except Ru and O, no other detected peak that related with any impurity element in the spectrum, i.e. the synthesized RuO2 is pure tetragonal RuO2 phase [2]. The TEM image was used to determine the shape, size and uniformity of the particles. The TEM image of the synthesized RuO2 is shown in Fig. 1c. It is observed that the particles are spherical in shape and monodispersed with a mean diameter of 8 nm, which are in well agreement with X-ray results. The SAED pattern of the synthesized magnetite is inset in Fig. 1c. It is clear that the RuO2 consisting of rings was consistent with a tetragonal structure of RuO2, which indicates a good crystallinity and a spatial configuration of well-defined grains boundary of the nanoparticles. The characteristic d-spacing corresponds to the miller indices (hkl) value (110), (101), (200), (211), (220), (310) and (301) showed a fully coincidence with X-ray results.

70

80

2 Theta / Degree

(b)

3.1 I–V characteristics of Ag/RuO2/p-Si/Al diode The electrical properties of Schottky diode junctions were analyzed byI–V and C–V measurements. The (I–V) characteristics of the RuO2/p-Si diode performed under dark and various illuminations are shown in Fig. 2. The inset of Fig. 2 is the schematic diagram of the fabricated Ag/RuO2/ p-Si/Al Schottky diode. It is evident from Fig. 2, that the fabricated diode shows a rectifying behavior in dark. The rectification andI–V characteristics are limited by the properties of the p-Si substrate and the magnitude of the energy barriers at the RuO2/p-Si-interface. The rectification ratio (RR) was found to be 112 at ±2 V. The maximum leakage current density was observed to be 15 through 22 nA/cm2 and no breakdown was observed up to ±4 V. Such behaviour can be analyzed by thermionic emission theory [26]. According to this model, the current through such diode could be expressed as [26, 27]: I ¼ I0 expðqðV  IRS Þ=nKT Þ½1  expððqðV  IRS Þ=KT ÞÞ

(c)

ð2Þ where I0 is the reverse saturation current, q is the electronic charge, V is the applied voltage, RS is the series resistance, n is the ideality factor, k is the Boltzmann constant and T is the temperature. The reverse saturation current (I0) is expressed by the following relation [27–30]:

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Fig. 1 a XRD pattern of polycrystalline RuO2 nanoparticles by sol– gel method. b EDS pattern of polycrystalline RuO2 nanoparticles by sol–gel method. c TEM of as synthesized RuO2 and the inset is EDS pattern of polycrystalline RuO2 nanoparticles by sol–gel method

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-3

H ðI Þ ¼ IRS  nub

10

ð6Þ

where -4

10

H ðI Þ ¼ V  n -5

I (A)

10

-6

10

In dark -2 5 mW.Cm -2 10 mW.Cm -2 20 mW.Cm -2 30 mW.Cm -2 40 mW.Cm -2 50 mW.Cm -2 60 mW.Cm -2 70 mW.Cm -2 80 mW.Cm

-7

10

-8

10

-9

10

-2.0 -1.6 -1.2 -0.8 -0.4 0.0 0.4 0.8 1.2 1.6 2.0

V (Volt)

Fig. 2 I–V characteristics of the Ag//RuO2/p-Si/Al diode under dark and various illuminations (inset figure shows the schematic diagram of the fabricated diode)

I0 ¼ AA T 2 exp

qu  b KT

ð3Þ

where A is the diode contact area, A is the effective Richardson constant (equal to 32 A/cm2 K2 for p-type silicon) and ub is the barrier height. The ideality factor was determined from the slope of the linear region of forward bias ln I–V plot. The barrier height of the device was calculated using Eq. (3). The ideality factor and barrier height of the Ag/RuO2/p-Si/Al Schottky diode were found to be 1.47 and 0.55 eV, respectively. The higher value of the ideality factor shows the presence of inhomogeneities of Schottky barrier height and existence of interface states, and series resistance [31, 32]. The deviation from ideal behavior the fabricated Ag/RuO2/p-Si/ Al diode can be explained on the basis of series resistance according to Cheung and Cheung method [31–33], where the I–V characteristics due to the thermionic emission of the diode having a series resistance can be expressed as following [34, 35]: I ¼ I0 expðqðV  IRS Þ=nKT Þ

ð4Þ

where IRS is the voltage drop across the series resistance and according to Cheung’s function, the series resistance, ideality factor and the barrier height can be calculated at low biasing voltage (V B0.4 V) [31–33]:   dV KT ¼n ð5Þ þ IRS dðln I Þ q and

    KT I ln q AA T 2

ð7Þ

By using Eq. (5), the series resistance and ideality factor of the diode can be calculated from the slope and y-axis intercept of the dV/d(ln I) versus I plot as shown in Fig. 3. The values of series resistance and ideality factor were calculated to be 52.4 9 103 X and 1.26 respectively. It is observed that there is a difference between the ideality factor obtained from the forward bias semi-log I–V plot and dV/d(ln I) versus I plot. This difference is ascribed to the presence of series resistance, interface states, and the voltage drop across the interfacial layer [34–37]. Also, by using Eqs. (6) and (7); the plot of H(I) versus I will lead to a straight line with y-axis intercept to nub and the series resistance was obtained from the slope of this straight line. The calculated values of ub and RS were found to be 0.63 eV and 59.4 9 103 X, respectively. It is worthy to note that the difference in the barrier heights obtained from I(V) and H(I) methods could be due to the fact that I–V characteristics uses the low voltage region for calculation, while H(I) versus I plot is applied to the full voltage range of forward bias characteristics of the diode [36, 37]. Also, we used the Norde method to investigate the values of the series resistance and the barrier height of the fabricated Ag/ RuO2/p-Si/Al diode and Norde function can be expressed by the following relation [35]:     F ðV Þ ¼ V= ðKT=qÞ ln I V=AA T 2 ð8Þ where c is the integer (dimensionless) [n, here it is taken as 5, I(V) is the current obtained from theI–V characteristics. The value of barrier height is calculated after getting minimum of the F versus V plot. Figure 4 shows the F(V) versus V plot of the device. The barrier height is given as [38, 39]: ub ¼ F ðVmin Þ þ Vmin 

KT q

ð9Þ

where F(Vmin) is the minimum point of F(V) and Vmin is the corresponding voltage. The value of series resistance is also calculated using the formula [39, 40]: RS ¼ KT ðc  nÞqImin :

ð10Þ

The values of barrier height and series resistance were determined to be 0.64 eV and 59.6 kX, respectively by using the n = 1.46. A small difference in values of series resistance obtained from Cheung’s and Norde’s method is observed. This difference may be due to the fact that Cheung’s model is applicable in the high-voltage region of

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1.00

0 x1 2.4

-1

H(I) vs I

H(I)=0.81+[56.3 10 ]*I Series Resistance=59.4 k .Ω Barrier Height= 0.63 eV

B D

0.95

-1

0 x1 1.6

0.90

-1

0 x1 1.2

0.85

H(I), (Volt)

dV/d[lnI], (Volt)

0 x1 2.0

dV/d[lnI] vs. I

-2

0 x1 8.0

dV/d[lnI]=0.0322+[52.4 10 ]*I n=1.26 RS=52.4 10 Ω

-2

0 x1 4.0

0.0

0.80

0.75 -7

-7

-6

-6

-6

-6

-6

-6

-7 0 10 10 10 10 10 10 10 0x1 00x10 7.50x 1.00x 1.25x 1.50x 1.75x 2.00x 2.25x 2.5 5.

I, (A)

Fig. 3 dV/d(lnI) versus I and H(V) versus I plots for the Ag/RuO2/Sip/Al diode at room temperature 0.84 0.82 0.80 0.78 F(V) vs. V

0.76

F(V)

0.74 0.72

The Calculated barrier height from Nord's method equal to 0.64 eV The calculated Series resistance equal to 59.6 kΩ

Iph ¼ APm

0.70 0.68 0.66 0.64 0.62 0.60 0.58 0.00

0.25

0.50

0.75

1.00

Fig. 5 indicate the presence of SCLC mechanism controlled by the traps; because the slope of I–V curves in double semi-log scale is [2 (m & 4.9, 2.5 and 3.5, respectively). In this case, the rate of increase of current with voltage decreases, until it becomes constant when all the traps are occupied. This region is usually described by a power law which assumes the filling of traps distributed exponentially within the band gap [38–41]. According to the I–V characteristic curve under forward biased voltage, the different slopes at the five investigated regions may be due to the presence of trap bands with different energies. This behavior may be due to the spin-coated dielectric material (RuO2); where its charge carriers have small mobility. The carriers of charges cannot reach to the collecting electrode at the same rate under the influence of the small steps of the applied forward biasing voltage. As a result, the presence of the traps in higher levels increases the quantity of charge carriers which reaches to the collecting electrode. In turn, the resultant forward current is influenced towards higher values with different rates. The photoresponse behavior of the fabricated Ag/RuO3/ p-Si/Al diode was studied under various illumination intensities. Figure 6 shows the variation of photocurrent with illumination intensity. The photocurrent behavior of the diode was analyzed by the following relation [25, 40]:

1.25

1.50

1.75

2.00

V, (Volt)

ð11Þ

where Iph is the photocurrent, A is a constant, m is an exponent and P is the light intensity. The value of m was determined from the slope of log(Iph) versus log(P) plot and was found to be 0.81. The obtained m value between 0.5 and 1 suggests the presence of continuous distribution of trap levels [28, 41]. The transient photocurrent study is a technique to understand the transport mechanism of the device. As seen in Fig. 7, the photocurrent of the diode

Fig. 4 The F(V) versus V plot of the Ag/RuO2/Si-p/Al diode -6

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II

I -9

VI

III

V

2.03

lnI-lnV Fit region-I Fit region-II Fit region-III Fit region-VI Fit region-V

-12

-18 2.02

IαV

-21

-4

-3

-2

IαV

4.9

-15

IαV

ln(I) (A)

the forward bias ln I–V characteristics, while Norde’s model is applied to the full-voltage range of forward bias ln I–V characteristics of the junctions [34, 35]. The conduction mechanism of Ag/RuO2/p-Si/Al diode was studied under forward biasing voltage by plotting the I–V characteristics in the double logarithmic form as shown in Fig. 5. The ln(I)–ln(V) plot clearly showed the power law behavior of current and voltage. The double semi-logarithmic plot of forward bias I–V characteristics had five linear regions. When the slope is approximately 2, the current density in this region can be expressed by a power law, i.e., I µ Vm [36, 37], with m & 2 as shown in Fig. 5. Thus, the region I and V are described by space charge limited current (SCLC) mechanism, which is usually described by the power law which assumes the trap distribution by single trap within the band gap. The regions II, III and VI in

2.5

IαV

3.5

IαV

-1

0

1

ln(V) (V)

Fig. 5 The ln(I)–ln(V) plot clearly showed the power law behavior of current and voltage for the Ag/RuO2/p-Si/Al diode

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Light off

Light off

Experimental measured photocurrent Simulated data

Cycle-I

Cycle-II

25

I (μ A)

20

15

5

0

0

10

Light on

Light on

10

20

30

40

50

60

70

80

90

100

110

t (s)

Fig. 7 I–t curve of the Ag/RuO2/p-Si/Al diode

-10

x10 1.6

500 kHz 600 kHz 700 kHz 800 kHz 900 kHz 1000 kHz

-10

x10 1.4

-10

x10 1.2

CADJ (F)

increases sharply after illumination the device and remains almost constant until the illumination is turned off. After switching off the illumination, the photocurrent decreases. The photocurrent of the Ag/RuO2/p-Si/Al diode is increased from 5.53 9 10-7 to 1.93 9 10-5 A, under illumination of power 80 mW/cm2. This suggests that the fabricated device exhibits a photoconducting behavior. The initial rise in the current indicates more generation of free charge carriers on illuminating the device. The photocurrent may take place via the transitions associated with defects and the photogenerated charge carriers can be trapped in defect levels. The trapped charge carriers may again recombine into another state and re-emitted into the conduction band [42–47]. The electron traps play an important role in the photoconductivity behavior of the diode. The traps in the spin coated RuO2 can be extremely deep levels and may therefore have very fast response, as observed in our data. The decay of the photocurrent after turning off the illumination is due to trapping of the electrons in the deep levels. After the illumination is turned off, the photocurrent will change according to the excess electron concentration and it will deplete upon recombination with holes emitted from hole traps. Thus, Ag/RuO2/ p-Si/Al could be used as an optical sensor in optoelectronic applications. Effects of frequency (500–1,000 kHz) and voltage (-2 to ?2 V) on the characteristics of capacitance and conductance of the Ag/RuO3/p-Si/Al diode were studied. Figure 8a, b shows the variations of measured capacitance, Cadj, and conductance, Gadj, respectively with applied voltage at different frequencies. As seen in Fig. 8a, at reverse biasing region, the value of Cadj did not change with frequency and the plot of Cadj versus V gives a peak around 0.25 and the peak intensity is decreased with

(a)

-10

x10 1.0

-11

x10 8.0

-11

x10 6.0

-11

x10 4.0

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

V (Volt) -4.6 -4

0 x1 6.0

-4.8 -4

0 x1 5.0

-4

GADJ (S)

Ip (A)

-5.0

-5.2

-5.4

0 x1 4.0

(b)

500 kHz 600 kHz 700 kHz 800 kHz 900 kHz 1000 kHz

-4

0 x1 3.0

-4

0 x1 2.0

-5.6

-5.8 0.6

-4

0 x1 1.0

0.8

0.9

1.0

1.2

1.3

1.5

1.6

1.8

2.0

2

P (mW/cm )

Fig. 6 Transient photocurrent versus power of the Ag/RuO2/p-Si/Al diode under 80 mW/cm2 light intensity

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

V (Volt)

Fig. 8 Frequency dependence a CADJ–V and b GADJ–V characteristics of the Ag/RuO2/p-Si/Al diode

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where h i a ¼ Gm  G2m þ ðx Cm Þ2 RS

ð14Þ

where CADJ and GADJ are series resistance compensated capacitance and conductance respectively. Figure 8a, b shows the CADJ–V and GADJ–V plots of the corrected values of capacitance and conductance as a function of frequencies ranging from 500 to 1,000 kHz, respectively. Figure 9 shows the variation of Gm, GADJ and CADJ with frequency of as fabricated diode. It is observed that the CADJ is decreased with increase in frequency, whereas Gm and GADJ increases with increase in frequency. At lower frequencies, the higher value of the capacitance results from the interface states, on the other hand at higher frequencies, the capacitance is not dispersive, as the charge at the interface cannot follow the fast AC signal and they do not contribute to the diode capacitance. This indicates the presence of interface states [25].

4 Conclusions Sol–gel technique showed a suitable method to prepare single phase RuO2. High-quality RuO2 thin films were successfully deposited on p-silicon and glass substrates by a spin coating technique. The XRD pattern shows that the

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-10

1.5

CADJ (F)

1.4

0 x1

1.2 1.1 1.0

GADJ-f

10

5.0x10

-4

4.0x10

-4

3.0x10

-4

2.0x10

-4

1.0x10

-4

Gm-f

-10

x 1.3

-4

CADJ-f

-10

x

6.0x10

10

-10

x1

0

-10

x1

0

-10

x

Gm or GADJ (s)

increasing frequency. This indicates the presence of interface states in the interface of the diode. Figure 8b shows an independent behavior between the applied AC signal and the Gadj at high reverse biasing region. The conductance of the diode increases with increasing frequencies. If the C–V measurement were performed at sufficiently high frequencies, the charge at the interface could not follow the AC signal [42, 43]. The observed decrease in the capacitance and increase in the conductance with increase in frequency, confirms the presence of interface states [44]. The higher value of the capacitance at low frequencies, results from the interface states [45]. It is seen that the conductance of the diode increases with increase in the frequency in the forward bias voltage. The corrected capacitance (CADJ), and corrected conductance (GADJ), were determined to eliminate the effect of series resistance on electrical properties of the diode. The CADJ and GADJ were calculated using the following expressions [45–47]. h i G2m þ ðx Cm Þ2 Cm CADJ ¼ ð12Þ a2 þ ðx Cm Þ2 h i G2m þ ðx Cm Þ2 a CADJ ¼ ð13Þ a2 þ ðx Cm Þ2

10

5x10

5

6x10

5

7x10

5

8x10

5

9x10

5

10

6

f (Hz)

Fig. 9 Plots ofCADJ, Gm and GADJ versus frequency of the Ag/RuO2/ p-Si/Al diode

grown film was polycrystalline in nature and the grains are highly oriented in (100) direction. The grown films are shown to have a large value of figure of merit. These results confirm the fact that RuO2 films grown by spin coating technique are very promising for crystalline silicon solar cells. The I–V characteristics under different light intensity suggest that the photoresponse of the fabricate diode is very sensitive to light intensity with very small diffusion current. The corrected capacitance and conductance were also estimated to eliminate the effect of series resistance on capacitance and conductance of the device. The C–V measurements indicate that the capacitance is independent of the voltage and frequency at higher positive voltage. The high value of capacitance at low frequency in reverse bias region is attributed to the excess capacitance resulting from the interface states that could follow the AC signal. Acknowledgments Thanks are due to the Deanship of Scientific Research at King Abdulaziz University, Jeddah, Saudi Arabia, for facilitating and support for the research group ‘‘Advances in composites, Synthesis and applications’’. This work is as a result of collaboration of the group with prof. F. Yakuphanoglu.

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