p-Type NiZnO thin films grown by photo-assist metal–organic chemical vapor deposition

doi:10.1016/j.jallcom.2013.04.192

Journal of Alloys and Compounds

Volume 579, 5 December 2013, Pages 160-164

https://doi.org/10.1016/j.jallcom.2013.04.192 Get rights and content

Highlights

•
The photo assist system can relieve the crystal quality degradation effectively.
•
The Ni and oxygen content have important effect on the characters of the films.
•
The p-NiZnO film can be obtained easily by controlling the Ni and oxygen content.

Abstract

NiZnO thin films with different Ni and O contents were grown by photo-assist metal–organic chemical vapor deposition. Electrical characteristics of films including resistances and charge carrier concentrations were analyzed. The intrinsic donor defects in NiZnO films could be effectively compensated by the increasing the Ni and O contents. A p-type NiZnO film with a high hole concentration could be obtained by controlling the Ni and O content of the film. This was further confirmed by analyzing defect levels from photoluminescence measurements.

Introduction

ZnO is a semiconductor with a wide band gap (3.37 eV) and large exciton binding energy (60 meV) at room temperature [1], [2], [3], [4]. It has been extensively studied because of its potential applications in light-emitting diodes [5], [6], [7], [8], [9], [10], laser diodes [11], solar cells [12] and photodetectors [13], [14], [15]. Undoped ZnO thin films exhibit typical n-type conductivity, caused by a deviation from uniform stoichiometry due to the low formation energy of intrinsic donor defects [16], [17], [18], [19], [20], [21], [22], [23]. Such defects hamper the realization of stable p-type ZnO and further applications of ZnO. In contrast, undoped NiO is an intrinsic p-type semiconductor with a band gap of 3.6–4.0 eV, which is attributed to the high concentration of intrinsic acceptor defects, such as Ni vacancies and interstitial O occupancy [24], [25], [26], [27], [28], [29]. Alloying ZnO and low-dose NiO can effectively reduce the electron concentration in ZnO films, and the ZnO band gap remains largely unchanged. Few papers to date have reported on the electrical characteristics of NiZnO thin films, especially those grown by photo-assist metal–organic chemical vapor deposition (PA-MOCVD) [30], [31], [32].

In the current study, NiZnO thin films were grown by PA-MOCVD. The electrical characteristics of these films including resistances and charge carrier concentrations were analyzed.

Section snippets

Experimental details

NiZnO thin films were grown on c-axis sapphire substrates by low-pressure PA-MOCVD. Substrates were first ultrasonically cleaned with methylbenzene, acetone, alcohol and then deionized water, each for 5 min. The substrate was placed in a growth chamber with base vacuum pressure of 3.0 × 10⁻⁴ Pa. Diethyl zinc (DEZn), NiMcP₂ and oxygen were used as the Zn, Ni and O sources, respectively. They were introduced into the reactor through separate injectors, to avoid any pre-reaction of metal–organic

X-ray diffraction (XRD) analysis

The crystal structure and orientation of Ni_xZn₁₋_xO films with different Ni contents (x = 0, 0.14, 0.2) were measured by D8 XRD, and the results are shown in Fig. 1. The pure ZnO film was transparent and preferentially oriented along the c-axis. Only one peak at 34.5° 2θ was observed, and corresponded to the (0 0 2) orientation. The (0 0 2) peaks of samples shifted to a higher diffraction angle (34.7° 2θ), when the value of x increased to 0.14. Bragg’s law [38] suggests this shift indicated a

Conclusions

NiZnO thin film with different Ni and O contents were grown by PA-MOCVD, and the electrical characteristics of these films were analyzed. For films of the same Ni content, resistance increased with increasing O flux, due to a decrease in intrinsic donor defects. For films with the same O flux, resistance increased with increasing Ni content, due to the increase in intrinsic acceptor defects. Similar trends were apparent from the charge carrier concentrations of the samples, and this conclusion

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Nos. 61006006, 60877020 and 60976010), the “973” program under Grant No. 2011CB30200001 and science and technology development project in Jilin province (No. 20100170).

References (43)

C.Y. Zhang
Mater. Sci. Semicond. Process.
(2007)
D.C. Look
Mater. Sci. Eng. B
(2001)
K. Wang et al.
Thin Solid Films
(2007)
Zhen Zhou et al.
J. Eur. Ceram. Soc.
(2004)
H. Sato et al.
Thin Solid Films
(1993)
Kenkichiro Kobayashi et al.
Thin Solid Films
(2008)
Guangqing Pei et al.
Scripta Mater.
(2007)
G.Q. Pei et al.
Curr. Appl. Phys.
(2008)
Xiangping Li et al.
Appl. Surf. Sci.
(2008)
M. Shimizu et al.
J. Cryst. Growth
(1989)

Q. Zhong et al.

Physica C

(1995)

J. Bian et al.

Chem. Phys. Lett.

(2006)

Yingrui Sui et al.

J. Appl. Phys.

(2013)

S.J. Pearton et al.

J. Vac. Sci. Technol.

(2004)

Zhifeng Shi et al.

Appl. Phys. Lett.

(2013)

A. Baltakesmez et al.

AIP Adv.

(2013)

Lanzhong Hao et al.

AIP Adv.

(2013)

X. Dong et al.

Semicond. Sci. Technol.

(2007)

J.C. Sun et al.

Appl. Phys. Lett.

(2007)

Ricky W. Chuang et al.

Appl. Phys. Lett.

(2007)

D.M. Bagnall et al.

Appl. Phys. Lett.

(1997)

Cited by (13)

Influence of nickel doping on the energy band gap, luminescence, and magnetic order of spray deposited nanostructured ZnO thin films
2020, Journal of Alloys and Compounds
Citation Excerpt :
These features have made ZnO based nanostructures and films as promising candidates for various applications in optoelectronic, solar cells, and spintronic devices [1–7]. For these purposes, doped ZnO films were synthesized by many methods, such as the thermal evaporation [7], molecular epitaxy [8], chemical vapor deposition [9], pulse laser deposition [10], sputtering [11], dip coating [12], spray pyrolysis [13], etc. Among all, spray pyrolysis is well proper for deposition of doped ZnO films due to its low cost, simplicity, control of doping, reproducibility and capability for uniform and homogeneous wide deposition.
We synthesized Ni doped ZnO thin films, Zn_xNi_1-xO $(0.0 \leq x \leq 0.1)$ , using spray pyrolysis deposition and performed a systematic study on their crystal structure, electronic, photoluminescent properties, and magnetic order. X-ray diffraction analysis showed that all nanostructured films under investigation are crystalized in a single phase wurtzite structure (space group P63mc), with a preferred orientation along (002) plane. The phase purity and the successful incorporation of Ni dopants into the ZnO lattice were also confirmed by the x-ray photoelectron spectroscopy (XPS), Ultra Violet-Visible, and Energy Dispersive X-ray spectroscopy measurements. The XPS results indicated that Ni ions are in 2 + oxidization state in all doped films. Photoluminescence (PL) spectroscopy showed strong emission peak in the UV region and multi-components emission peak in the visible luminescence, which is ascribed to deep-level emissions by different types of intrinsic defect states. Both XPS and PL spectroscopy clearly showed significant enhancement in the oxygen vacancy (V_O) concentration by increasing the Ni doping. The saturation magnetization and coercivity also increase with Ni doping, indicating a strong correlation between the concentration of V_O defects, and the observed magnetic order in the doped films. In addition, a red shift in the energy gap is found with Ni doping and is attributed to the sp–d exchange interaction, which is mediated by the V_O defects in the ZnO lattice.
High hole concentration Li-doped NiZnO thin films grown by photo-assisted metal–organic chemical vapor deposition
2016, Journal of Crystal Growth
Citation Excerpt :
The PA-MOCVD method has been employed in numerous studies because it significantly reduces the degradations in crystal quality caused by the alloying and doping processes [24–26]. The mole content of Ni in the samples was set to 14% in accordance with the optimized results of earlier studies [27]. Samples with Li mole contents of 0, 1%, and 2% were grown by the traditional MOCVD method (without PA) and these samples were labeled A, B, and C, respectively.
High hole concentration Li-doped NiZnO thin films were grown by metal–organic chemical vapor deposition (MOCVD). The crystalline, optical, electrical, and morphological characteristics of the NiZnO films were studied as a function of lithium content. The resistance of the films decreased and the hole concentration greatly increased with increasing lithium content. However, the crystalline and optical properties were observed to degrade as the lithium content was increased. To relieve the degradation, a photo-assisted MOCVD method was used in order to restrict this degradation and this represents a new way to obtain stable high hole concentration NiZnO films.
Structural, optical and conductivity studies of amorphous Zn<inf>x</inf>Ni<inf>1-x</inf>O thin films along with wettability and photocatalytic tests
2016, Journal of Non-Crystalline Solids
Citation Excerpt :
It can be explained that the nickel atoms brought the nickel interstitial and oxygen vacancy in NiZnO alloy. Ni and O contents greatly affected the concentration of OZn and Oi, in agreement with the optical characteristics results described above [24]. Complex impedance curves of Z″ as a function of Z′ in temperature range (330–450 °C) are displayed in Fig. 10.
Non-crystalline zinc nickel oxide has been deposited on glass substrate using spray pyrolysis. The structural and optical properties were examined using XRD and UV–visible spectrophotometry. These films are characterized by a direct band gap and the optical band gap energy value is lying between 3.66 eV and 3.79 eV. The electrical conductivity was investigated at different temperatures (330–450 °C) by using the impedance spectroscopy technique in a frequency range from 5 Hz to 13 MHz. The value of s is dependent on temperature, which tends to decrease depending on the temperature. The temperature dependence of both the AC conductivity and the parameter s is interpreted by the correlated barrier hopping (CBH) model. These films revealed a hydrophilic character. Moreover, in the presence of these samples, a photodegradation of methyl blue (MB) and effective mineralization occurred; 14 mg/L of MB was degraded within 120 min. Finally, elements from the Lattice Compatibility Theory were presented in order to understand partial non-crystallization of the ZnO-NiO binary structure.
Preparation of ZnO films with variable electric field-assisted atomic layer deposition technique
2014, Applied Surface Science
Citation Excerpt :
It is well-known that structures of the deposited ZnO films are dependent on the preparing approaches and conditions. Several techniques have been reported to fabricate ZnO films, such as magnetron sputtering [16,17] pulsed laser deposition (PLD) [18,19], chemical vapor deposition (CVD) [20,21], molecular beam epitaxy (MBE) [22], electrodeposition [23] and sol–gel deposition [24]. In recent years, the atomic layer deposition (ALD) technique has been intensively adopted to obtain high-quality thin films [25–28].
The ZnO films have been prepared by a variable electric field-assisted atomic layer deposition method (ALD). By applying electric fields during the precursor pulses, we can modulate both the crystal orientation and structure of the obtained ZnO films. The ZnO films with c-axis preferred orientation and the least oxygen vacancy defect were obtained when the holder electric polarities were positive and negative during the DEZn and H₂O pulse, respectively. It is supported that when electric field was applied in the chamber, the torque may lead to the precursor molecular alignments along the electric field direction, which could affect the film growth process and then influence their structures and properties. This variable electric field-assisted ALD approach would provide an efficient protocol for the growth of semiconductor films with designed properties.
Effect of nickel doping on physical properties of zinc oxide thin films prepared by the spray pyrolysis method
2014, Applied Surface Science
Citation Excerpt :
Self-assembly using physical and chemical methods has been extensively explored for generating complex nanostructures on various scales [20–22], but the methods yield either the nanostructures. Many techniques have been employed to prepare ZnO thin films: chemical vapor deposition [23], pulsed laser deposition [24], radio frequency magnetron sputtering [25], and spray pyrolysis [26]. In this paper, we report the influence of Ni doping on the structural, morphological, optical and electrical properties of ZnO films.
In this study, undoped and nickel-doped zinc oxide thin films (ZnO:Ni) were deposited on glass substrates using a spray pyrolysis technique. The effects of the Zn concentration in the initial solution and the substrate temperature on the physical properties of the thin films are studied. The results show that the optimum Zn concentration and substrate temperature for preparation of basic undoped ZnO films with n-type conductivity and high optical transparency are 0.02 M and 350 °C, respectively. Then, by using these optimized deposition parameters, nickel-doped zinc oxide films are prepared. Surface morphology and crystalline structure of the films are investigated by atomic force microscopy (AFM) and X-ray diffractometer. X-ray diffraction (XRD) patterns show that the films are polycrystalline. The structural analysis shows that all the samples have a hexagonal structure. The crystallite size and the preferred orientation were calculated from the XRD data. From AFM investigations, the surface morphology of the nanostructured films is found to depend on the concentration of Ni. Optical measurements have shown that an increase in the Ni doping results in a reduction in the optical transmission of the layer, but it remains higher than 80% for Ni doping greater than 8 wt%. At the same time, the optical gap increases from 3.4 to 4 eV when the Ni ratio increases. The electrical measurements show that the resistance of the films varies with the duration of pulverization and the nickel content of the film. Low values for the electrical resistivity (around 10³ Ω cm) were obtained for Ni-doped ZnO thin films.
Structural and optical properties of ZnSO alloy thin films with different S contents grown by pulsed laser deposition
2014, Journal of Alloys and Compounds
Citation Excerpt :
Due to the significant difference between S stabilization and ZnO film growth temperature, S has rarely been doped in ZnO [25]. The growth of ZnO film usually needs a high growth temperature [26,27], while S is stable only at a low temperature. Moreover, the intermediate phases such as ZnSO4 could be formed because S is reactive to O.
ZnSO thin films with different S contents were deposited on quartz substrates by pulsed laser deposition. X-ray diffraction patterns suggested that all the films have a hexagonal wurtzite ZnO structure with a highly c-axis orientation. XPS measurements confirmed the alloying behavior of S. EDS results revealed that S content in ZnSO films could be modulated by the growth temperature and efficient S alloying can be achieved under low growth temperatures. The composition dependence of the band gap energy in ZnSO system was determined by optical transmission and the optical bowing parameter was found to be about 2.13 eV.

View all citing articles on Scopus

View full text

p-Type NiZnO thin films grown by photo-assist metal–organic chemical vapor deposition

Highlights

Abstract

Introduction

Section snippets

Experimental details

X-ray diffraction (XRD) analysis

Conclusions

Acknowledgments

Mater. Sci. Semicond. Process.

Mater. Sci. Eng. B

Thin Solid Films

J. Eur. Ceram. Soc.

Thin Solid Films

Thin Solid Films

Scripta Mater.

Curr. Appl. Phys.

Appl. Surf. Sci.

J. Cryst. Growth

Physica C

Chem. Phys. Lett.

J. Appl. Phys.

J. Vac. Sci. Technol.

Appl. Phys. Lett.

AIP Adv.

AIP Adv.

Semicond. Sci. Technol.

Appl. Phys. Lett.

Appl. Phys. Lett.

Appl. Phys. Lett.