Properties Of N-doped ZnO Films Research Articles

Effects of Post-Annealing Temperature on the Structure and Electrical Properties of N-Doped ZnO Films

N-doped ZnO films were deposited on Si (100) substrates by radio frequency (RF) magnetron sputtering in N2/Ar2gas mixture. After the deposition, the films were post-annealed in vacuum at several temperatures from 400°C to 850°C for 60 minutes respectively.X-ray diffraction (XRD), atomic force microscope (AFM), Hall measurements setup (Hall) were used to analyze the structure, morphology and electrical properties of ZnO films.The results show that growth are still preferred (002) orientation of ZnO films following post-annealing. When the annealing temperature is higher than 650°C achieved by the n-type ZnO to the p-type transition and for the better growth of p-type ZnO films, the optimal annealing temperature is 650°C.

Luminescence behavior and compensation effect of N-doped ZnO films deposited by rf magnetron sputtering under various gas-flow ratios of O2/N2

The photoluminescent and electrical properties of N-doped ZnO films fabricated by rf magnetron sputtering under various gas-flow ratios of O2/N2 were examined in this study. The dependence of conduction type on the gas-flow rate of O2/N2 was found. The authors identified a direct correlation between the defect spectral feature and conduction type of N-doped ZnO samples and provided a physical model for producing p-type ZnO. According to these observed results, the authors suggested that p-type conversion of N-doped ZnO may be due to a combined effect of the increased acceptor (substitutional nitrogen in oxygen site, zinc vacancy and interstitial oxygen) density and the decreased donor (oxygen vacancy) density. In addition, synthesis of p-type N-doped ZnO was repeated, suggesting that p-type ZnO can be fabricated with excellent reproducibility by rf magnetron sputtering a ZnO target doped with nitrogen.

Properties of N-Doped ZnO Films by RF Magnetron Sputtering

Using the radio frequency reactive magnetron sputtering technique, ZnO:N thin films were fabricated on glass substrate by changing the Ar/N2 flow ratio from 9/1 to 9/4. The samples were characterizated on the film microstructure and optical properties by XRD, UV- visible spectrophotometer and Fourier transform infrared spectroscopy. The XRD results show that no significant peaks appeared at less N flow and the light transmission rate of UV-Vis has Small fluctuations between 320~780nm wavelength ; with increasing N flow, there was only (002) single peak in curves of XRD, transmittance of UV had a sharp decline below the 400nm wavelength; when argon-nitrogen flow ratio was increased to 9/4, it is show that there were two peaks near 34°of 2θ in curves of XRD but no significant change in UV transmittance.

Structural, optical and electrical properties of N-doped ZnO thin films prepared by thermal oxidation of pulsed filtered cathodic vacuum arc deposited Zn xN y films

In this study, N-doped ZnO thin films were fabricated by oxidation of Zn x N y films. The Zn x N y thin films were deposited on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) using metallic zinc wire (99.999%) as a cathode target in pure nitrogen plasma. The influence of oxidation temperature, on the electrical, structural and optical properties of N-doped ZnO films was investigated. P-type conduction was achieved for the N-doped ZnO obtained at 450 °C by oxidation of Zn x N y , with a resistivity of 16.1 Ω cm, hole concentration of 2.03 × 10 16 cm −3 and Hall mobility of 19 cm 2/V s. X-ray photoelectron spectroscopy (XPS) analysis confirmed the incorporation of N into the ZnO films. X-ray diffraction (XRD) pattern showed that the films as-deposited and oxidized at 350 °C were amorphous. However, the oxidized films in air atmosphere at 450–550 °C were polycrystalline without preferential orientation. In room temperature photoluminescence (PL) spectra, an ultraviolet (UV) peak was seen for all the samples. In addition, a broad deep level emission was observed.

Influence of oxygen partial pressure on properties of N-doped ZnO films deposited by magnetron sputtering

N-doped ZnO films were radio frequency (RF) sputtered on glass substrates and studied as a function of oxygen partial pressure (OPP) ranging from 3.0×10 −4 to 9.5×10 −3 Pa. X-ray diffraction patters confirmed the polycrystalline nature of the deposited films. The crystalline structure is influenced by the variation of OPP. Atomic force microscopy analysis confirmed the agglomeration of the neighboring spherical grains with a sharp increase of root mean square (RMS) roughness when the OPP is increased above 1.4×10 −3 Pa. X-ray photoelectron spectroscopy analysis revealed that the incorporation of N content into the film is decreased with the increase of OPP, noticeably N 1s XPS peaks are hardly identified at 9.5×10 −3 Pa. The average visible transmittance (380-700 nm) is increased with the increase of OPP (from ∼17% to 70%), and the optical absorption edge shifts towards the shorter wavelength. The films deposited with low OPP (≤ 3.0×10 −4 Pa) show n-type conductivity and those deposited with high OPP (≥ 9.0×10 −4 Pa) are highly resistive (>10 5 Ω·cm)

Influence of nitrogen on the defects and magnetism of ZnO:N thin films

Nitrogen (N)-doped ZnO thin films have been deposited on Si (100) substrates by pulsed laser deposition under different N2 pressures. The optical and magnetic properties of N-doped ZnO films have been studied with photoluminescence, Raman spectroscopy, and vibrating sample magnetometer. Photoluminescence and Raman studies reveal that N2 pressure affected the defects of N-doped ZnO films. Under 10 Pa N2 pressure, N substitutes O and forms NO acceptor. Zn interstitials are main compensating donors. Under higher N2 pressures, N not only substitutes O but also forms N2O molecules in N-doped ZnO films. Zn antisizes are compensating donors. In additional, Zn vacancies are formed and the concentration increases with increasing N2 pressure. Magnetic properties of these films show that there are two distinct ferromagnetic mechanisms: the origin of ferromagnetism in the ZnO:N-10 Pa film is Zn interstitial, while Zn vacancy leads to ferromagnetism in the ZnO:N-50 Pa film.

Induced changes on visible emission and conductive type in N-doped ZnO films by rapid thermal process

The erratic p-type conductivity in nitrogen-doped ZnO film is still under investigation and has been debated up to now. In this study, the authors have studied the effect of rapid thermal process (RTP) on the properties of N-doped ZnO films grown by metal-organic chemical vapor deposition. Hall-effect measurements show that the sample is of p-type as the RTP temperature is lower than 350 °C while, as the RTP temperature increased up to 550 °C or higher, the conduction-type of the sample changed to be n-type. Correspondingly, obvious D and G peaks, which are related to graphite clusters, are observed to increase their intensity with RTP temperature, indicating that interstitial or substitutional carbon atoms may migrate to form carbon clusters in the grain boundary during RTP. RTP is also found to lead to significant changes on the photoluminescence of the samples, with enhanced visible emissions observed as RTP temperature increased. Similar changes are observed on the intensity ratios of the D over G peaks and the visible emission around 600 nm over the near-band-edge emission. This indicates that besides zinc vacancy (VZn) and oxygen vacancy (VO), which are popularly ascribed as the origins of the visible emissions around 500 and 550 nm, carbon clusters may be a possible origin of the visible emission around 600 nm. Finally, carbon clusters formed in the grain boundary are also supposed to at least partly be responsible for the type transition caused by RTP.

Temperature effect on the electrical, structural and optical properties of N-doped ZnO films by plasma-free metal organic chemical vapor deposition

N-doped p-type ZnO films were grown by plasma-free metal-organic chemical vapor deposition (MOCVD). The effect of substrate temperature on the electrical, optical, and structural properties of the N-doped ZnO films was investigated by Hall-effect, photoluminescence, X-ray diffraction measurements. The electrical properties of the films were extremely sensitive to the substrate temperature and the conduction type could be reversed in a narrow range from 380 °C to 420 °C. Based on X-ray photoelectron spectroscopy, a high compensation effect in the N-doped ZnO films grown by plasma-free MOCVD was suggested to explain the temperature-dependent phenomenon.

Influence of unintentional doped carbon on growth and properties of N-doped ZnO films

The evolution of optical and electrical properties induced by rapid thermal annealing is studied on nitrogen-doped ZnO samples grown by metal-organic chemical vapor deposition (MOCVD). Correspondingly, in the Raman spectra carbon cluster related D and G modes have been observed to increase with annealing temperature. The increase in the intensity ratio of D and G modes indicates growing of carbon clusters, revealing an interesting change in unintentional doped carbon, which is a popular impurity in MOCVD grown N-doped ZnO. Substitutional or interstitial carbons in the grains may migrate to grain boundaries to incorporate with some existing carbon clusters to form larger ones. Accordingly, zinc vacancies will then be easily formed as annealing temperature increased, resulting in eminent green band emission at room temperature photoluminescence. The band edge emissions also show significant changes with several shoulders observed by thermal annealing, which can be ascribed to acceptor or donor related emissions. The changes in emissions agree well with the evolution of the electrical property of annealed samples. This study shows that unintentional doped carbon has a great influence on ZnO growth by forming clusters in the grain boundary area and also on the optical and electrical properties by forming C related defects in the grains.

Effect of Annealing Temperature on Structural and Optical Properties of N-Doped ZnO Films

Nitrogen-doped ZnO (ZnO:N) films are prepared by thermal oxidation of sputtered Zn3N2 layers on Al2O3 substrates. The correlation between the structural and optical properties of ZnO:N films and annealing temperatures is investigated. X-ray diffraction result demonstrates that the as-sputtered Zn3N2 films are transformed into ZnO:N films after annealing above 600° C. X-ray photoelectron spectroscopy reveals that nitrogen has two chemical states in the ZnO:N films: the NO acceptor and the double donor (N2)O. Due to the No acceptor, the hole concentration in the film annealed at 700° C is predicted to be highest, which is also confirmed by Hall effect measurement. In addition, the temperature dependent photoluminescence spectra allow to calculate the nitrogen acceptor binding energy.

Effect of annealing on the properties of N-doped ZnO films deposited by RF magnetron sputtering

N-doped ZnO films were deposited by RF magnetron sputtering in N 2/Ar gas mixture and were post-annealed at different temperatures ( T a) ranging from 400 to 800 °C in O 2 gas at atmospheric pressure. The as-deposited and post-annealed films were characterized by their structural (XRD), compositional (SIMS, XPS), optical (UV–vis–NIR spectrometry), electrical (Hall measurements), and optoelectronic properties (PL spectra). The XRD results authenticate the improvement of crystallinity following post-annealing. The weak intensity of the (0 0 2) reflection obtained for the as-deposited N-doped ZnO films was increased with the increasing T a to become the preferred orientation at higher T a (800 °C). The amount of N-concentration and the chemical states of N element in ZnO films were changed with the T a, especially above 400 °C. The average visible transmittance (400–800 nm) of the as-deposited films (26%) was increased with the increasing T a to reach a maximum of 75% at 600 °C but then decreased. In the PL spectra, A 0X emission at 3.321 eV was observed for T a = 400 °C besides the main D 0X emission. The intensity of the A 0X emission was decreased with the increasing T a whereas D 0X emission became sharper and more optical emission centers were observed when T a is increased above 400 °C.

Properties of Zn 3N 2-doped ZnO films deposited by pulsed laser deposition

The optical properties of N-doped ZnO films grown by pulsed laser deposition are examined for which zinc nitride is used as the source of nitrogen. The motivation for this study is to determine if nitrogen-related acceptor state formation can be achieved in ZnO films using Zn 3N 2 doping in the ablation target. The films were deposited in oxygen or nitrogen on c-plane sapphire. Photoluminescence measurements at 20 K reveal a 3.31 eV acceptor-bound exciton emission due to nitrogen substitution on the oxygen site, donor–acceptor pair emission at 3.23 ± 1 eV and free electron-acceptor at 3.27 eV. The binding energy of the N-related acceptor is estimated to be in the range of 170–15 meV. While the as-deposited films were n-type, thermal annealing in oxygen yielded insulating behavior, consistent with compensating acceptor states.

Influence of Codoping with Ga on the Electrical and Optical Properties of N-Doped ZnO Films

This study reports on the dependence on Ga concentration of the electrical and optical properties of ZnO films doped at a N concentration of For Ga concentrations below 0.5 mol %, the N concentration was kept at However, as the Ga concentration increased to 5 mol %, the N concentration suddenly increased from to Furthermore, the donor-acceptor pair emission and yellow luminescence in N single-doped ZnO films were suppressed significantly by doping with Ga at a concentration of 0.1 mol %. However, doping with Ga concentrations above 0.5 mol % resulted in increased red luminescence originating from deep levels generated through the excessive incorporation of Ga atoms. An evaluation of the crystalline quality and electrical properties indicated that the Ga atoms located on the Zn sites changed largely from shallow donor sources to compensating defects trapping electrons at Ga concentrations in the 0.5 to 5 mol % range. These results suggested that the increased N concentration and the enhancement of ultraviolet (UV) emission could be attributed to the role played by the Ga atoms located on the Zn sites in the N single-doped ZnO films. © 2003 The Electrochemical Society. All rights reserved.

Structural, electrical and optical properties of N-doped ZnO films synthesized by SS-CVD

N-doped p-type ZnO films have been synthesized on α-Al 2O 3 (0 0 0 1) substrate by solid-source chemical vapor deposition using Zn(CH 3COO) 2·2H 2O as the precursor and CH 3COONH 4 as the nitrogen source. The properties for ZnO films are dependent greatly on the growth conditions. Results show that the best electrical properties of the p-type film, such as carrier density N=9.8×10 17 cm −3 , resistivity ρ=20 Ω cm and Hall mobility μ=0.97 cm 2/ V s , were induced at the substrate temperature of 500°C with a precursor temperature of 250°C and a nitrogen source of 150°C, under which the highest mixed orientation for (1 0 0) and (1 1 0) planes of films was also achieved. The p-type ZnO films possess a transmittance of about 90% in visible region and a band gap of about 3.20 eV at room temperature.