p-Si heterojunction prepared by ultrasonic spray pyrolysis

Accepted Manuscript Morphological and optoelectrical study of ZnO:In/p-Si heterojunction prepared by ultrasonic spray pyrolysis

F. Ynineb, N. Attaf, M.S. Aida, J. Bougdira, Y. Bouznit, H. Rinnert PII: DOI: Reference:

S0040-6090(17)30143-8 doi: 10.1016/j.tsf.2017.02.044 TSF 35824

To appear in:

Thin Solid Films

Received date: Revised date: Accepted date:

22 March 2016 15 February 2017 15 February 2017

Please cite this article as: F. Ynineb, N. Attaf, M.S. Aida, J. Bougdira, Y. Bouznit, H. Rinnert , Morphological and optoelectrical study of ZnO:In/p-Si heterojunction prepared by ultrasonic spray pyrolysis. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Tsf(2017), doi: 10.1016/ j.tsf.2017.02.044

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Morphological and optoelectrical study of ZnO:In/p-Si heterojunction prepared by ultrasonic spray pyrolysis

F. Ynineb

a

, N. Attaf b, M.S. Aida b, J. Bougdira c, Y. Bouznit

d

and H. Rinnert

c

Development Center of Advanced Technologies (CDTA), UROP, Sétif, 19000, Algeria

PT

Laboratory of Thin Films and Interfaces, Constantine University, Constantine, 25000, Algeria Lorraine University, Jean Lamour Institute UMR 7198, Vandoeuvre, 54506, France

d

Laboratory of Materials : Elaborations-Properties-Applications, Jijel University, Jijel 18000, Algeria

Corresponding Author: E-mail: [email protected]

NU

*

RI

c

SC

b

a,b*

MA

Tel.: +213795647027; Fax: + 21331818664.

Keywords: Zinc oxides, Ultrasonic spray pyrolysis, Heterojunction, Photoluminescence.

D

Abstract

PT E

Indium doped zinc oxide thin films were deposited on p-type Si (100) substrates using ultrasonic spray pyrolysis technique (ZnO:In/p-Si heterojunction). The structural, morphological and optical

CE

properties of In-doped ZnO films have been investigated. The X-ray diffraction spectra and scanning electron microscopy measurements indicated that the films are of polycrystalline nature

AC

with (002) preferential orientation and a surface morphology almost homogeneous. The photoluminescence measurements showed that the films present some intrinsic defects such as oxygen vacancies and zinc interstitials. Current-voltage and capacitance-voltage (C-V) measurements revealed an ideality factor (n) values (in the range of 1,12 to 2,82), which are higher than unity due to the oxide layer and the presence of interface states between the two semiconductor materials. The barrier height is in the range of 0,65 – 0,73 eV and the junction builtin voltage deduced from C-V measurements is in the range of 0,64 – 0,94 V at room temperature.

1

ACCEPTED MANUSCRIPT 1. Introduction Recently, zinc oxide (ZnO) becomes a very popular material due to its great potential in various optoelectronics applications. It is an n-type II-VI semiconductor with a hexagonal wurtzite structure and direct wide band gap of 3,37 eV and large exciton binding energy of 60 meV [1-3]. This material presents other interesting properties such as chemical and thermal stability, availability, nontoxicity and low cost compared with other materials, which makes it a good candidate for

PT

industrial applications where it is applied widely in optoelectric devices as a type of transparent

RI

conducting oxides like front contact in solar cells, UV lasers or LEDs.

ZnO thin films can be deposited onto different substrates using several kinds of techniques

SC

including R.F. sputtering [4], chemical bath deposition [5], pulsed laser deposition [6], metalloorganic chemical vapor deposition [7], sol-gel process [8] and spray pyrolysis [9]. This last is a

NU

simple technique, cost effective and suitable for large area thin film preparation with homogenous

MA

doping level [9, 10]. For instance, Aida and his research group [9, 11, 12] have widely studied ZnO thin films deposited by ultrasonic spray pyrolysis technique on different substrates and determined their structural, optical and electrical properties. Recently, quite a lot of research groups have

D

devoted to fabrication of ZnO based junctions due to potential applications in optoelectronic

PT E

devices. ZnO/Si heterojunctions are of particular interest using hybrid advantages of large binding energy of ZnO thin films and the inexpensiveness of Si substrates. In such heterojunctions, the

CE

structural, morphological and optical properties have been well studied, however few reports have been devoted to electrical characteristics despite their importance in solar cells and LEDs diodes

AC

applications [13-15].

In the present study, ZnO:In/p-Si heterojunction was realized by the deposition of In-doped ZnO thin films directly on p-Si substrate using ultrasonic spray pyrolysis method. The first part of this work is devoted to the investigation of indium doping level influence on structural, morphological and optical properties of In-doped ZnO thin films. The second part deals with the investigation of electrical characterizations of ZnO:In/p-Si heterojunctions by means of current-voltage and capacitance-voltage measurements at various indium doping levels.

2

ACCEPTED MANUSCRIPT 2. Experimental Undoped and In-doped ZnO thin films were deposited on silicon and glass substrates using ultrasonic spray pyrolysis technique. The silicon used in the experiment was p-type (boron-doped) single crystal with (100) orientation and 1-10 Ω.cm resistivity. The glass and silicon substrates were treated in standard cleaning procedure, rinsed in deionized water and acetone, cleaned ultrasonically and dried. Just before deposition, the silicon substrates were etched in hydrogen

PT

fluoride (HF) solution for 5 min, to remove the native oxide layer on wafers. The sprayed solution

RI

was prepared using 0,05 M zinc acetate dehydrate (Zn(CH3COOH)2, H2O) dissolved in methanol as a solvent and by adding indium chloride (InCl3), as a dopant. To investigate the effect of indium

SC

doping level on heterojunction properties, the weight ratio of indium chloride to zinc acetate was varied from 0 to 4 wt.%. After stirring for 30 min, a clear and homogeneous solution was obtained.

NU

The ultrasonic generator and dropping system are regulated to obtain a continuous spray flux onto

MA

substrates. The spraying rate was of 10 ml/h. The substrate temperature was fixed at 350 °C and the deposition time for 5 min. For current-voltage (I-V) and capacity-voltage (C-V) measurements, gold contacts were deposited as a back contact onto all Si surface and as a front contact onto the

D

ZnO surface, by circular dots of 2 mm in diameter and 100 nm thickness, using EDWARDS sputter

PT E

coter S 150B in a pressure of 1,33 x10-2 Pa. The schematic illustration of the sandwich contact Au/ZnO:In/p-Si/Au of elaborated heterojunctions is shown in Fig.1. The ohmicity of all these

CE

contacts was checked.

The ZnO films thickness was determined using KLA-TENCOR P6 profilometer. The measured

AC

films thicknesses are ranged from 349 nm to 354 nm. Structural properties were investigated by Xrays diffraction (XRD) analysis using X’PertPro MPD diffractometer with Cu Kα radiation (CuKα= 1,541 Å) in  configuration. The diffractometer reflections of all films were taken at room temperature and the values of 2θ were altered between 30° and 80°. The surface morphology of the samples was studied using a FEG 7600F JEOL scanning electron microscopy (SEM) The working distance for all samples was 15 mm, the accelerate voltage was 20 kV, and the probe current was 1 nA. The chemical composition of the films has been determined using an energy dispersive X-rays spectrometer (EDX) coupled to FEG 7600F JEOL Scanning Electron Microscope 3

ACCEPTED MANUSCRIPT (with a SDD detector). Incident electron beam energy used was 15 keV. The electron beam was at normal incidence to the sample surface. For the successful quantitative analysis, ZAF correction has been taken into account. The optical transmittance measurements were carried out on glass substrates, in the wavelength range 300-650 nm using a double beam spectrophotometer 3101 PC-Shimadzu. For photoluminescence (PL) measurements, the excitation was obtained with a 200 W mercury arc lamp source, using the ultraviolet lines at 313 and 334 nm. The PL signal was

PT

analyzed by a monochromator equipped with a 150 grooves/mm grating and by a charge-coupled

RI

device camera detector cooled down to 140 K. The response of the detection systems was precisely calibrated with a tungsten wire calibration source. The current–voltage (I–V)

SC

measurements were performed in dark at room temperature using TEKTRONIX 370 and a KEITHLEY 617 sourcemeter. And finally, capacitance-voltage (C-V) characteristics were recorded

NU

using a capacitance meter KEITHLEY 590 CV analyzer.

MA

3. Results and discussion 3.1. Structural and morphological study

Fig.2 shows the XRD patterns of In-doped ZnO thin films. The analysis of XRD data reveal the

D

peaks corresponding to the (002), (101), (102), (103), and (112) planes of ZnO hexagonal wurtzite

PT E

structure (according to the JCPDS Card File No.: 36-1451). This result suggests that the deposited films are polycrystalline with (002) as preferential orientation (i.e. c-axis orientation is perpendicular

CE

to the substrate) which is adversely affected by subsequent indium doping of films. The preferential (002) peak intensity increases at 1wt.% In-doping indicating an improvement in

AC

films crystallinity. This is due to the fact that the indium incorporated, at low level, into the lattice is considered as an inhibitor of new nucleation sites [11]. However, increasing indium doping level: (2wt.% and 4wt.%) favors the formation of new nucleation sites. Thereafter, the (002) peak intensity decreases and the preferential orientation changed to (101) [16]. In this case, the films growth is not dominant along one orientation, but according to both (101) and (002) directions. This behavior is explained by Goyal et al. [17] on the basis of variations in the lattice parameters with the dopant level caused by the shift in the angular positions of the reflection peaks [18].This shift is probably results from a combination of Zn+2 ion replacement by the In+3 ions in the wurtzitestructured ZnO lattices [19, 20] and the film stress induced during the deposition process [21]. 4

ACCEPTED MANUSCRIPT To estimate the average crystallite sizes in these In-doped ZnO thin films, Scherrer's formula was applied [22] for the (002) peak. ZnO crystallite size is not affected noticeably by indium doping level; it’s varied between 33 nm and 26 nm (Table 1). In Fig.3(a-d), we have reported the SEM images of the In-doped ZnO thin films used in ZnO:In/p-Si heterojunctions. As seen, all films exhibit a homogeneous surface. The morphology of undoped ZnO thin film (Fig.3.a) is composed of lamellar shapes stacked and disoriented with an average

PT

size of 70 nm. However, films morphology, grain size and shape are slightly altered by In-doping

RI

(Fig.3.b-d), films structure remains dense and compact with a nanoscale grain size. It worth noting that the lamellar structure is an effective structure for light trapping which is useful for solar cells

SC

[23].

The EDX spectrum of undoped ZnO thin film shown in Fig.4.(a) exhibits peaks relating to Zn and O

NU

elements. Similar peaks are also observed in the spectrum of 4wt.% In-doped ZnO film (Fig.4.(b))

MA

with emergence of two smaller peaks corresponding to In atoms. The presence of Si peaks in both spectra is related to silicon substrate. The insets in both images (Fig.4.a and b) show elemental weights (wt.%) and atomics (at.%) of Zn, O and In in undoped and In-doped ZnO thin films. The

D

indium atomic composition in film network is low; it is in the order of 0,31at.% for highly doped film.

PT E

Actually, the amount of doping atoms in films is less than its value in the starting solution. Similar observations were reported in the case of Zn doped SnO2 [24] and Cd doped ZnO [25]. The high

CE

atomic content of O in the two films suggests the presence of a strong defect density of oxygen interstitials (Oi) and zinc vacancies (VZn) in the films as will be shown in room-temperature

AC

photoluminescence analysis. These results are in good agreement with other results reported in the literature [26, 27]. 3.2. Optical study

The effect of indium doping on optical properties of ZnO films has been studied. Fig.5 shows the transmission spectra recorded in the range from 300 to 650 nm obtained in samples prepared with various In-doping levels. As shown in this figure, all films exhibit high transparency (between 85 and 90%) in the visible region with a sharp fundamental absorption edge characteristic of ZnO. This absorption edge has a blue shift to the region of higher photon energy with an increase in In-

5

ACCEPTED MANUSCRIPT doping level (as indicated by the arrow in Fig.5). The absence of the interference fringes in these spectra indicates that the obtained films have a rough surface. The inset in Fig.5 displays the evolution of band gap energy (Eg) with indium doping level, calculated from (αhν)2-hν curves of elaborated films. It is clear that, with increasing in In-doping level, the films band gap energy increases from 3,28 to 3,31 eV due to the Burstein-Moss effect [28, 29]. According to this effect, the increase of the Fermi level in the conduction band leads to a

PT

widening of band gap energy with increasing of free charges (electrons) concentration. The same

RI

conclusion has been reported by Machado et al. [30] in In-doped ZnO thin films deposited by electrodeposition method.

SC

Fig.6 shows the room-temperature photoluminescence (RTPL) spectra of undoped and In-doped ZnO thin films with various doping levels. The RTPL spectrum of the undoped ZnO film consists of

NU

three typical emission peaks, namely: near band edge (NBE) emission peak centered at 375 nm

MA

and a broad green and deep levels (DL) emissions peaks centered at 515 nm (green emission) and another at around 750 nm (red emission) [31]. The NBE emission is attributed to the free excitons recombination [32-34], while the DL emissions are assigned to the intrinsic defects in the

D

obtained films [35, 36]. For ZnO films, It is well known (according to literature) that the oxygen

PT E

vacancies (VO) and the zinc interstitials (Zni) are responsible for the green emission (500-520 nm) [37-39], while the red emission (700-750 nm) is attributed to the oxygen interstitials (Oi) and the

CE

zinc vacancies (VZn) [40, 41].Therefore, these four kinds of defects are originating of the two DL emissions detected in undoped ZnO thin film. This result is confirmed in EDX part where there was

AC

an excess of oxygen in our films. From RTPL measurements, it is worth noting that NBE emission peak has a blue shift to higher energy with In-doping level, which is a good agreement with the observation from the optical transmission measurements, and his intensity was affected by the doping level, this can be explained in terms of films crystallinity evolution with In incorporation in film network. Nevertheless, the incorporation of indium in ZnO affects the photoluminescence significantly; disappearance of green (bump at 515 nm) and red emissions (bump at 750 nm). According to EDX analysis (Fig.4), films are oxygen rich, thereafter; the main origin of green emission is due to the Zni and less from VO, while the red emission can be mainly due to the Oi. 6

ACCEPTED MANUSCRIPT The incorporation of indium atoms during films doping, is followed by the reduction of both defects Zni and Oi, the latter are substituted [42, 43] by indium in the interstitial position since the indium ionic radius is lower than Zn and O ionic radius (In radius 0,62, Zn 0,68 and O 1,35 Å). This can explain then the observed disappearance of green and red emission with indium films doping. 3.3. Electrical study of ZnO:In/p-Si heterojunction 3.3.1. Dark current-voltage characteristics

PT

Current-voltage measurements (I-V) provide a valuable source of information about several

RI

junction parameters such as ideality factor (n), reverse saturation current (Is) and barrier height energy (qΦb). The current-voltage characteristics of ZnO:In/p-Si heterojunctions measured at RT

SC

(300 K) for both forward and reverse biases are shown in Fig.7. It is observed from this figure that I-V curves of obtained heterojunctions show a good rectifying behavior at all heterojunctions where

NU

the forward current increase exponentially with increasing in the forward bias voltage.

MA

The current-voltage relation of a p-n heterojunction is usually written as a function of the applied voltage (V) as [44, 45]:

D

(1)

PT E

Where V is voltage bias and Is is the saturation current which can be determined by an extrapolation of the forward bias LnI-V curve to V=0. It is defined by: (2)

CE

With A* the theoretical Richardson constant taken as 32 A.cm-2.K-2 for ZnO [46], S the area of the

AC

diode, qΦb the barrier height energy (eV) and k Boltzmann’s constant. n is the ideality factor that measures the conformity of the diode to pure thermionic emission. It can be calculated from the slope of the straight line region of the forward bias Ln(I)-V plot and can be written as: (3) In the literature, if n varies between 1 and 2, the tunneling current mechanism is dominant. If n=2, the generation-recombination current mechanism is the dominant. If n˃2, it means the leakage current mechanism is dominant [47]. The barrier height energy (qΦb) is calculated by the following formula:

7

ACCEPTED MANUSCRIPT (4) The electrical parameters values of obtained ZnO:In/p-Si heterojunctions determined from I-V characteristics were summarized in Table 2. It is known that the ideality factor in an ideal p-n heterojunction is around 1 at a low voltage and up to 2 at a higher voltage according to the Sah–Noyce– Shockley theory [48]. The ideality factor

PT

values higher than unity suggests the non-ideal behavior of heterojunctions originate from the presence of an oxide layer or/and the presence of interface states [49, 50]. The variation of ideality

RI

factor and barrier height energy values with indium doping level is shown in Fig.8. The values of n

SC

and qΦb are ranged from 2,82 and 0,73 eV (at 0 wt.% In) to 1,12 and 0,65 eV (at 4 wt.% In), respectively. As can be seen, the values of both n and qΦb decreased with increasing in doping

NU

level. Because of the barrier inhomogeneity and presence of defects at the heterojunctions, the current transport will be dominated by patches with lower qΦb [51]. With incorporation of indium

MA

ions in ZnO lattice, the interface states density decreases due to saturation of some of these states by electrons coming from indium doping. Consequently, both barrier height and ideality factor

D

decrease. The obtained n and qΦb values in this study are in good agreement with that reported by

PT E

Gayen et al. (2,38 and 0,74 eV) [52] and by Keskenler et al. (2,03 and 0,71 eV) [53] for ZnO/p-Si heterojunctions.

3.3.2. Dark capacitance-voltage characteristics

CE

From capacitance-voltage measurements (C-V), some junction parameters can be determined as built-in voltage (Vbi) and donor concentration of ZnO (Nd) [54]. Fig.9.a gives the C-V characteristics

AC

in the reverse bias region at RT of different elaborated ZnO:In/p-Si heterojunctions. The results show that the capacitance is inversely proportional to the bias voltage. The decrease in the capacitance with increasing in indium doping content and reverse bias may originate from the space-charge region broadening with doping level. The linear relationship between 1/C2 and reverse bias (Fig.9.b) indicates that the charge transition behavior from the donor to the acceptor region was found to be abrupt. The built-in voltage Vbi (the diffusion potential at zero bias) can be calculated by extrapolating 1/C2–V plot to the point 1/C2 = 0. The intercept voltage Vint is related to the Vbi by: 8

ACCEPTED MANUSCRIPT (5) where kT/q is the volt equivalent of temperature. The slope of the straight line gives the donor concentration Nd, which its values correspond well with the known resistivity of silicon substrates. The built-in voltage and donor concentration values of obtained ZnO:In/p-Si heterojunctions are summarized in Table 2. The obtained values of the built-in voltage at RT are in the range of 0,64 – 0,94 V, which are lower than that reported by Zebbar et al. (1,14 V) [15] and by Zhang et al. (1,19

PT

V) [55] in nanocrystalline ZnO/Si heterostructure.

RI

The band diagram energy of ZnO:1wt.%In film showing intrinsic defects levels, and that of the

SC

elaborated ZnO:1wt.%In/p-Si heterojunction using the Anderson model [44] are shown in Fig.10. According to PL data, the intrinsic defects present in this film are oxygen interstitials and the zinc

NU

vacancies (E = 1,65 eV). For band diagram energy of ZnO:1wt.%In/p-Si heterojunction, the band gap energy (Eg) and electron affinity (χ) values used are Eg(Si) = 1,12 eV and χ(Si) = 4,05 eV, Eg(ZnO)

MA

= 3,30 eV and χ(ZnO) = 4,35 eV [8, 49]. Due to the differences in the electron affinities and the band gaps of the two materials, both the conduction and the valence bands have band offsets. The

D

conduction band offset (ΔEC = χ(ZnO) - χ(Si)) and valence band offset (ΔEV = Eg(ZnO) + χ(ZnO) – Eg(Si) -

PT E

χ(Si)) of the ZnO:1wt.%In/p-Si heterojunction were estimated to be 0,3 and 2,48 eV respectively [56, 57]. It is found that the valence band offset is much larger than the conduction band offset in this case. The higher barrier in the valence band prevents the movement of holes from p-Si to ZnO.

CE

Therefore, the current transport in the present heterojunction device is determined predominantly by the flow electrons in the conduction band from ZnO:1wt.%In to p-Si [58, 59].

AC

4. Conclusion

We report the realization of ZnO:In/p-Si heterojunction by ultrasonic spray pyrolysis method. In order to optimize the experimental conditions, the influence of indium doping level on ZnO:In thin films properties is investigated. The obtained results indicate that films properties are very affected by indium doping level. The optimized ZnO:1%wt.In/p-Si heterojunction exhibits a good rectifying behavior and giving low ideality factor and saturation current (2,22 and 3,38×10-1 µA respectively). The ideality factor higher than 2, indicating that thermionic emission is not the only conduction mechanism for the current flow due to the oxide layer and the presence of surface states. These 9

ACCEPTED MANUSCRIPT results suggest that the grown ZnO:In by ultrasonic spray pyrolysis method can be used to fabricate efficient heterojunctions. This work is helpful in the development of ZnO/p-Si

AC

CE

PT E

D

MA

NU

SC

RI

PT

heterojunctions.

10

ACCEPTED MANUSCRIPT References [1]

X.L. Xu, S.P. Lau, J.S. Chen, Z. Sun, B.K. Tay, J.W. Chai, Dependence of electrical and optical properties of ZnO films on substrate temperature, Materials Science in Semiconductor Processing 4 (2001) 617-620.

[2]

U. Ozgur, Y.I. Alivov, C. Liu, A. Teke, M.A. Reshchikov, S. Dogan, V. Avrutin, S.-J. Cho, H. Morkoç, A comprehensive review of ZnO materials and devices, J. Appl. Phys. 98 (2005) 041301.

[3]

Z. Yang, S. Chu, W.V. Chen, L. Li, J. Kong, J. Ren, P.K.L. Yu, J. Liu, ZnO:Sb/ZnO:Ga Light

PT

Emitting Diode on c-Plane Sapphire by Molecular Beam Epitaxy, Appl. Phys. Express 3 (2010) 032101.

F. Chaabouni, M. Abaab, B. Rezig, Characterization of n-ZnO/p-Si films grown by magnetron

RI

[4]

sputtering, Superlattices and Microstructures 39 (2006) 171–178.

S. Hariech, M.S. Aida, H. Moualkia, Observation of Meyer-Neldel rule in CdS thin films,

SC

[5]

Materials Science in Semiconductor Processing 15 (2012) 181–186. G. Kaur, A. Mitra, K.L. Yadav, Pulsed laser deposited Al-doped ZnO thin films for optical

NU

[6]

applications, Progress in Natural Science: Materials International 25 (2015) 12–21. Y. Zhang, G. Du, B. Zhang, Y. Cui, H. Zhu, Y. Chang, Properties of ZnO thin films grown on

MA

[7]

Si substrates by MOCVD and ZnO/Si heterojunctions, Semicond. Sci. Technol. 20 (2005) 1132-1135.

S. Aksoy, Y. Caglar, Effect of ambient temperature on electrical properties of nanostructure

D

[8]

n-ZnO/p-Si heterojunction diode, Superlattices and Microstructures 51 (2012) 613–625. F. Ynineb, A. Hafdallah, M.S. Aida, N. Attaf, J. Bougdira, H. Rinnert, S. Rahmane, Influence

PT E

[9]

of Sn content on properties of ZnO:SnO2 thin films deposited by ultrasonic spray pyrolysis, Materials Science in Semiconductor Processing 16 (2013) 2021–2027.

CE

[10] S. Sali, M. Boumaour, S. Kermadi, A. Keffous, M. Kechouane, Effect of doping on structural, optical and electrical properties of nanostructure ZnO films deposited onto a-Si:H/Si

AC

heterojunction, Superlattices and Microstructures 52 (2012) 438–448. [11] A. Hafdallah, F. Yanineb, M.S. Aida, N. Attaf, In doped ZnO thin films, Journal of Alloys and Compounds 509 (2011) 7267–7270. [12] N. Lehraki, M.S. Aida, S. Abed, N. Attaf, A. Attaf, M. Poulain, ZnO thin films deposition by spray pyrolysis: Influence of precursor solution properties, Current Applied Physics 12 (2012) 1283-1287. [13] S. Majumdar, S. Chattopadhyay, P. Banerji, Electrical characterization of p-ZnO/p-Si heterojunction, Applied Surface Science 255 (2009) 6141-6144. [14] M. Kumar, S.K. Kim, S.-Y. Choi, Formation of Al–N co-doped p-ZnO/n-Si (100) heterojunction structure by RF co-sputtering technique, Applied Surface Science 256 (2009) 1329-1332.

11

ACCEPTED MANUSCRIPT [15] N. Zebbar, Y. Kheireddine, K. Mokeddem, A. Hafdallah, M. Kechouane, M.S. Aida, Structural, optical and electrical properties of n-ZnO/p-Si heterojunction prepared by ultrasonic spray, Materials Science in Semiconductor Processing 14 (2011) 229–234. [16] S. Ilican, Y. Caglar, M. Caglar, F. Yakuphanoglu, Electrical conductivity, optical and structural properties of indium-doped ZnO nanofiber thin film deposited by spray pyrolysis method, Physica E 35 (2006) 131–138. [17] D.J. Goyal, C. Agashe, M.G. Takwale, B.R. Marathe, V.G. Bhide, Development of transparent and conductive ZnO films by spray pyrolysis, Journal of materials science 27 (1992) 4705-

PT

4708.

[18] M. Krunks, E. Mellikov, Zinc oxide thin films by the spray pyrolysis method, Thin Solid Films

RI

270 (1995) 33-36.

[19] S.D. Shinde, A.V. Deshmukh, S.K. Date, V.G. Sathe, K.P. Adhi, Effect of Ga doping on

SC

micro/structural, electrical and optical properties of pulsed laser deposited ZnO thin films, Thin Solid Films 520 (2011) 1212-1217.

NU

[20] R. Ghosh, D. Basak, The effect of growth ambient on the structural and optical properties of MgXZn1-XO thin films, Applied Surface Science 255 (2009) 7238–7242. [21] L. Li, L. Fang, X.M. Chen, J. Liu, F.F. Yang, Q.J. Li, G.B. Liu, S.J. Feng, Influence of oxygen

MA

argon ratio on the structural, electrical, optical and thermoelectrical properties of Al-doped ZnO thin films, Physica E 41 (2008) 169-174.

[22] B.D. Cullity, S.R. Stock, Elements of X-Ray Diffraction, third ed., Prentice Hall, 2001.

D

[23] S.-S. Lin, J.-L. Huang, D.-F. Lii, The effects of r.f. power and substrate temperature on the

PT E

properties of ZnO films, Surf. Coat. Technol. 176 (2004) 173-181. [24] S. Vijayalakshmi, S. Venkataraj, M. Subramanian, R. Jayavel, Physical properties of zinc doped tin oxide films prepared by spray pyrolysis technique, J. Phys. D: Appl. Phys. 41

CE

(2008) 035505.

[25] S. Vijayalakshmi, S. Venkataraj, R. Jayavel, Characterization of cadmium doped zinc oxide

245403.

AC

(Cd:ZnO) thin films prepared by spray pyrolysis method, J. Phys. D: Appl. Phys. 41 (2008)

[26] A. Abdel Aal, S.A. Mahmoud, A.K. Aboul-Gheit, Sol–Gel and Thermally Evaporated Nanostructured Thin ZnO Films for Photocatalytic Degradation of Trichlorophenol, Nanoscale Res. Lett. 4 (2009) 627-634. [27] K.J. Chen, F.Y. Hung, S.J. Chang, Z.S. Hu, Microstructures, optical and electrical properties of In-doped ZnO thin films prepared by sol–gel method, Applied Surface Science 255 (2009) 6308-6312. [28] E. Burstein, Anomalous Optical Absorption Limit in InSb, Phys. Rev. 93 (1954) 632-633. [29] T. S. Moss, The Interpretation of the Properties of Indium Antimonide, Proc. Phys. Soc. B 67 (1954) 775-782.

12

ACCEPTED MANUSCRIPT [30] G. Machado, D.N. Guerra, D. Leinen, J.R. Ramos-Barrado, R.E. Marotti, E.A. Dalchiele, Indium doped zinc oxide thin films obtained by electrodeposition, Thin Solid Films 490 (2005) 124-131. [31] N.H. Alvi, M. Riaz, G. Tzamalis, O. Nur, M. Willander, Fabrication and characterization of high-brightness light emitting diodes based on n-ZnO nanorods grown by a low-temperature chemical method on p-4H-SiC and p-GaN, Semicond. Sci. Technol. 25 (2010) 065004. [32] D. Raoufi, Synthesis and photoluminescence characterization of ZnO nanoparticles, Journal of Luminescence 134 (2013) 213-219.

PT

[33] P. Zu, Z.K. Tang, G.K.L. Wong, M. Kawasaki, A. Ohtomo, H. Koinuma, Y. Segawa, Ultraviolet spontaneous and stimulated emissions prom ZnO microcrystallite thin films at room

RI

temperature, Solid Slate Communications 103 (1997) 459-463.

[34] S. Cho, J. Ma, Y. Kim, Y. Sun, G.K.L. Wong, J.B. Ketterson, Photoluminescence and

SC

ultraviolet lasing of polycrystalline ZnO thin films prepared by the oxidation of the metallic Zn, Appl. Phys. Lett. 75 (1999) 2761-2763.

NU

[35] B. Lin, Z. Fu, Y. Jia, Green luminescent center in undoped zinc oxide films deposited on silicon substrates, Applied Physics Letters 79 (2001) 943-945.

Appl. Phys. 49 (1978) 1188-1195.

MA

[36] E.G. Bylander, Surface effects on the low-energy cathodoluminescence of zinc oxide, J.

[37] S.S. Kurbanov, G.N. Panin, T.W. Kim, T.W. Kang, Strong violet luminescence from ZnO nanocrystals grown by the low-temperature chemical solution deposition, Journal of

D

Luminescence 129 (2009) 1099-1104.

PT E

[38] T.M. Borseth, B.G. Svensson, A.Y. Kuznetsov, P. Klason, Q.X. Zhao, M. Willander, Identification of oxygen and zinc vacancy optical signals in ZnO, Appl. Phys. Lett. 89 (2006) 262112.

3073.

CE

[39] C. Klingshirn, ZnO: From basics towards applications, Phys. Stat. Sol. (b) 244 (2007) 3027-

[40] Z. Fan, P.-C. Chang, J.G. Lu, E.C. Walter, R.M. Penner, C.-H. Lin, H.P. Lee,

AC

Photoluminescence and polarized photodetection of single ZnO nanowires, Appl. Phys. Lett. 85 (2004) 6128-6130. [41] J.W.P. Hsu, D.R. Tallant, R.L. Simpson, N.A. Missert, R.G. Copeland, Luminescent properties of solution-grown ZnO nanorods, Appl. Phys. Lett., 88 (2006) 252103. [42] H. Ryoken, I. Sakaguchi, N. Ohashi, T. Sekiguchi, S. Hishita, H. Haneda, Non-equilibrium defects in aluminum-doped zinc oxide thin films grown with a pulsed laser deposition method, J. Mater. Res. 20 (2005) 2866-2872. [43] K.U. Sim, S.W. Shin, A.V. Moholkar, J.H. Yun, J.H. Moon, J.H. Kim, Effects of dopant (Al, Ga, and In) on the characteristics of ZnO thin films prepared by RF magnetron sputtering system, Current Applied Physics 10 (2010) 463–467. [44] S. M. Sze, Kwok K. Hg, Physics of Semiconductor devices, third ed., New York: Wiley, 1981. 13

ACCEPTED MANUSCRIPT [45] S.K. Cheung, N.W. Cheung, Extraction of Schottky diode parameters from forward currentvoltage characteristics, Appl. Phys. Lett. 49 (1986) 85-87. [46] C.S. Singh, G. Agarwal, G. Durga Rao, S. Chaudhary, R. Singh, Effect of hydrogen peroxide treatment on the electrical characteristics of Au/ZnO epitaxial Schottky diode, Materials science in Semiconductor Processing 14 (2011) 1-4. [47] I. Ay, H. Tolunay, The influence of ohmic back contacts on the properties of a-Si:H Schottky diodes, Solid-State Electronics 51 (2007) 381-386. [48] C.-T. Sah, R.N. Noyce, W. Shockley, Carrier Generation and Recombination in P-N Junctions

PT

and P-N Junction Characteristics, Proc. IRE 45 (1957) 1228-1243.

[49] P. Chen, X. Ma, D. Yang, Ultraviolet electroluminescence from ZnO/p-Si heterojunctions, J.

RI

Appl. Phys. 101 (2007) 053103.

[50] H. Zhou, G. Fang, L. Yuan, C. Wang, X. Yang, H. Huang, C. Zhou, X. Zhao, Deep ultraviolet

SC

and near infrared photodiode based on n-ZnO/p-silicon nanowire heterojunction fabricated at low temperature, J. Appl. Phys. 94 (2009) 013503.

NU

[51] M.K. Hudait, P. Venkateswarlu, S.B. Krupanidhi, Electrical transport characteristics of Au/nGaAs Schottky diodes on n-Ge at low temperatures, Solid-State Electronics 45 (2001) 133141.

MA

[52] R.N. Gayen, S.R. Bhattacharyya, Electrical characteristics and rectification performance of wet chemically synthesized vertically aligned n-ZnO nanowire/p-Si heterojunction, J. Phys. D: Appl. Phys. 49 (2016) 115102.

D

[53] E.F. Keskenler, M. Tomakin, S. Dogan, G. Turgut, S. Aydın, S. Duman, B. Gürbulak, Growth

PT E

and characterization of Ag/n-ZnO/p-Si/Al heterojunction diode by sol-gel spin technique, Journal of Alloys and Compounds 550 (2013) 129-132. [54] E.K. Evangelou, N. Konofaos, M.R. Craven, W.M. Cranton, C.B. Thomas, Characterization of

CE

the BaTiO3/p-Si interface and applications, Applied Surface Science 166 (2000) 504-507. [55] Y. Zhang, J. Xu, B. Lin, Z. Fu, S. Zhong, C. Liu, Z. Zhang, Fabrication and electrical characterization of nanocrystalline ZnO/Si heterojunctions, Applied Surface Science 252

AC

(2006) 3449-3453.

[56] S. Chirakkara, S.B. Krupanidhi, Study of n-ZnO/p-Si (100) thin film heterojunctions by pulsed laser deposition without buffer layer, Thin Solid Films 520 (2012) 5894-5899. [57] J.H. Lee, B.R. Jang, J.Y. Lee, H.S. Kim, N.W. Jang, B.H. Kong, H.K. Cho, K.R. Bae, W.J. Lee, Y. Yun, Effect of Indium Mole Fraction on the Diode Characteristics of ZnO:In/p-Si(111) Heterojunctions, Japanese Journal of Applied Physics 50 (2011) 031101. [58] Z.-X. Fu, B.-X. Lin, G.-H. Liao, Photovoltaic Effect of ZnO/Si Heterostructure, Chin. Phys. Lett. 16 (1999) 753-755. [59] J.H. He, S.T. Ho, T.B. Wu, L.J. Chen, Z.L. Wang, Electrical and photoelectrical performances of nano-photodiode based on ZnO nanowires, Chemical Physics Letters 435 (2007) 119-122.

14

ACCEPTED MANUSCRIPT Figures and tables captions Fig.1. Schematic illustration of the sandwich contact Au/ZnO/p-Si/Au. Fig.2. XRD patterns of ZnO thin films deposited on glass substrate as a function of indium doping concentration (0, 1, 2 and 4 wt.% In). Table 1 Crystallite size values and (002) peak intensity of deposited In-doped ZnO thin films. Fig.3. SEM images of (a) undoped ZnO and In-doped ZnO thin films deposited on glass substrate

PT

at various weight concentrations: (b) 1 wt.% In, (c) 2 wt.% In and (d) 4wt.% In.

RI

Fig.4. EDX spectra of (a) undoped ZnO and (b) 4 wt.% In-doped ZnO thin films deposited on glass substrate.

SC

Fig.5. Transmittance and band gap energy of undoped and In-doped ZnO thin films prepared on glass substrate.

NU

Fig.6. Room temperature photoluminescence spectra of undoped and In-doped ZnO thin films

MA

deposited on p-type Si substrates.

Fig.7. Current-voltage characteristics of ZnO:In/p-Si heterojunctions at room temperature. Table 2 Electrical parameters of ZnO:In/p-Si heterojunctions measured at room temperature.

D

Fig.8. Variation of ideality factor (n) and barrier height energy (qϕb) versus doping level of ZnO

PT E

layer.

Fig.9. Capacitance-voltage characteristics C-V (a) and corresponding C-2-V (b) of ZnO:In/p-Si

CE

heterojunctions at room temperature. Fig.10. Schematic band diagram of ZnO:1wt.%In film showing intrinsic defects levels and that of

AC

ZnO:1wt.%In/p-Si heterojunction at zero bias voltage.

15

RI

PT

ACCEPTED MANUSCRIPT

SC

Au n-ZnO p-Si

MA

NU

Au

AC

CE

PT E

D

Fig.1

16

V

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig.2

17

c

PT

b

NU

SC

RI

a

MA

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

d

Fig.3

18

ACCEPTED MANUSCRIPT

a Wt.(%)

At.(%)

19,28 23,15 52,57

40,02 33,28 26,70

Energy

PT E

D

MA

Full Scale 4579 cps Cursor: 10.851 (0 cps)

NU

SC

RI

Element OK Si K Zn L

Spectrum 1

PT

a

Spectrum 2

b b b

Wt.(%)

At.(%)

19,70 30,97 48,23 1,09

39,97 35,78 23,94 0,31

AC

CE

Element OK Si K Zn L In L

keV

Energy

Full Scale 4202 cps Cursor: 10.851 (0 cps)

Fig.4

19

keV

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig.5

20

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig.6

21

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig.7

22

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig.8

23

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig.9

24

ZnO:1%In Film

SC

RI

p-Si

PT

ACCEPTED MANUSCRIPT

NU

χ=4,05eV EC

χ=4,35eV

ΔEC=0,3eV

MA

Eg=1,12eV EF EV

Evacuum

Interface states

Oi ~ 1,65 eV

VZn ~ 1,65 eV

Eg=3,30eV EV

Fig.10

AC

CE

PT E

D

ΔEV=2,48eV

EC EF

25

RI

PT

ACCEPTED MANUSCRIPT

0

1

D (nm)

33,50

26,09

I (002) (a.u.)

2770

3159

2

4

31,68

28,45

1751

608

MA

NU

wt.% In

SC

Tab.1

Tab.2

n

Is (A/cm2)

qϕb (eV)

Vbi (V)

Nd(cm-3)

0

2,82

9,44×10-8

0,73

0,64

3,11×1017

1

2,22

3,38×10-7

0,70

0,91

4,41×1017

1,18

1,39×10-6

0,66

0,69

6,24×1017

1,12

-6

0,65

0,94

7,68×1017

2,16×10

AC

CE

4

PT E

2

D

wt.% In

26

ACCEPTED MANUSCRIPT Highlights ZnO:In/p-Si heterojunctions were synthesized using ultrasonic spray pyrolysis method.



Effect of indium doping on physical properties of ZnO layer is investigated



Indium doping improves the films crystallinity and reduces the intrinsic defects in ZnO films



The characteristic parameters of ZnO:In/p-Si heterojunctions were determined.

AC

CE

PT E

D

MA

NU

SC

RI

PT



27