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 A1203 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℃. 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℃ 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.     

Identification of Acceptor States in Li-N Dual-Doped p-Type ZnO Thin Films

Li-N dual-doped p-type ZnO （ZnO：（Li, N）） thin films are prepared by pulsed laser deposition. The optical properties are studied using temperature-dependent photoluminescence. The Lizn-No complex acceptor with an energy 1evel of 138 me V is identified from the free-to-neutral-acceptor （e, A0 ） emission. The Haynes factor is about 0.087 for the Lizn-No complex acceptor, with the acceptor bound-exciton binding energy of 12meV. Another deeper acceptor state located at 248 meV, also identified from the （e, A0） emission, is attributed to zinc vacancy acceptor. The two acceptor states might both contribute to the observed p-type conductivity in ZnO：（Li,N）.     

Optical properties of p-type ZnO doped by lithium and nitrogen

A lithium and nitrogen doped p-type ZnO (denoted as ZnO: (Li, N)) film was prepared by RF-magnetron sputtering and post annealing techniques with c-Al₂O₃ as substrate. Its transmittance was measured to be above 95%. Three dominant emission bands were observed at 3.311, 3.219 and 3.346 eV, respectively, in the 80 K photoluminescence (PL) spectrum of the p-type ZnO:(Li, N), and are attributed to radiative electron transition from conduction band to a Li_Zn-N complex acceptor level (eFA), radiative recombination of a donor-acceptor pair and recombination of the Li_Zn-N complex acceptor bound exciton, respectively, based on temperature-dependent and excitation intensity-dependent PL measurement results. The Li_Zn-N complex acceptor level was estimated to be about 126 meV above the valence band by fitting the eFA data obtained in the temperature-dependent PL spectra.     

The photoluminescence characterization of the N-doped ZnO films produced by wet chemical deposition

The ZnO:N films are prepared by a wet chemical method. The temperature-dependent photoluminescence (PL) is used to investigate those ZnO: N films. Due to the introduction of nitrogen atoms into ZnO film, another phase appears in the ZnO film, which can release the stress and improve the film quality. As a result, a neutral donor-bound exciton (D⁰X) emission peak is shown in low temperature PL spectrum. With the increasing temperature, the D⁰X line gradually loses its intensity and shifts to 3.30 eV, which is consistent with the well-known conversion from bound exciton to free exciton at elevated temperatures. Then, due to the thermal quenching effect, the D⁰X line vanishes in room temperature. In addition, no shift is shown in the location of visible band emission and only the intensity decreases with the increasing temperature.     

Effects of Annealing Temperature on Structural and Optical Properties of ZnO Thin Films

The effects of annealing temperature on the structural and optical properties of ZnO films grown on Si （100） substrates by sol-gel spin-coating are investigated. The structural and optical properties are characterized by x-ray diffraction, scanning electron microscopy and photoluminescence spectra. X-ray diffraction analysis shows the crystal quality of ZnO films becomes better after annealing at high temperature. The grain size increases with the temperature increasing. It is found that the tensile stress in the plane of ZnO films first increases and then decreases with the annealing temperature increasing, reaching the maximum value of 1.8 GPa at 700℃. PL spectra of ZnO films annealed at various temperatures consists of a near band edge emission around 380 nm and visible emissions due to the electronic defects, which are related to deep level emissions, such as oxide antisite （OZn）, interstitial oxygen （Oi）, interstitial zinc （Zni） and zinc vacancy （VZn^-）, which are generated during annealing process. The evolution of defects is analyzed by PL spectra based on the energy of the electronic transitions.     

Studies of luminescence properties of ZnO and ZnO:Zn nanorods prepared by solution growth technique

Pyramidal ZnO nanorods with hexagonal structure having c-axis preferred orientation are grown over large area silica substrates by a simple aqueous solution growth technique. The as-grown nanorods were studied using XRD, SEM and UV-vis photoluminescence (PL) spectroscopy for their structural, morphological and optical properties, respectively. Further, the samples have also been annealed under different atmospheric conditions (air, O₂, N₂ and Zn) to study the defect formation in nanorods. The PL spectra of the as-grown nanorods show narrow-band excitonic emission at 3.03 eV and a broad-band deep-level emission (DLE) related to the defect centers at 2.24 eV. After some mild air annealing at 200 °C, fine structures with peaks having energy separation of ∼100 meV were observed in the DLE band and the same have been attributed to the longitudinal optical (LO) phonon-assisted transitions. However, the annealing of the samples under mild reducing atmospheres of N₂ or zinc at 550 °C resulted in significant modifications in the DLE band wherein high intensity green emission with two closely spaced peaks with maxima at 2.5 and 2.7 eV were observed which have been attributed to the V_O and Zn_i defect centers, respectively. The V-I characteristic of the ZnO:Zn nanorods shows enhancement in n-type conductivity compared to other samples. The studies thus suggest that the green emitting ZnO:Zn nanorods can be used as low voltage field emission display (FED) phosphors with nanometer scale resolution.     

Blue-to-Orange Tunable Luminescence from Europium Doped Yttrium--Silicon--Oxide--Nitride Phosphors

Europium-doped yttrium-silicon-oxide-nitride phosphors are synthesized by carbothermal reduction and nitridation method. The crystal structure of the phosphors changed gradually from oxide Y2Si2O7 to nitride YSi3N5 state with increasing dosage of Si3N4 and carbon powder. The Y2Si2O7：Eu phosphor shows a blue emission at 465 nm with 300 nm excitation and a characteristic red emission of Eu^3＋ at 612 nm with 230 nm excitation. The YSi3N5：EU phosphor shows a broad emission band centred at 595nm with some sharp peaks of Eu^3＋ with 325nm excitation. The absorption of the studied phosphors increases from 450 to 700hm with an increment in nitrogen content. Blue-to-orange tunable luminescence is observed with 390 nm excitation.     

Photoluminescence properties of nitrogen-doped ZnO films deposited on ZnO single crystal substrates by the plasma-assisted reactive evaporation method

Photoluminescence (PL) spectra of nitrogen-doped ZnO films (ZnO:N films) grown epitaxially on n-type ZnO single crystal substrates by using the plasma-assisted reactive evaporation method were measured at 5 K. In PL spectra, free exciton emission at about 3.375 eV was very strong and emissions at 3.334 and 3.31 eV were observed. These two emissions are discussed in this paper. The nitrogen concentration in ZnO:N films measured by secondary ion mass spectroscopy was 10^19-20 cm⁻³. Current-voltage characteristics of the junction consisting of an n-type ZnO single crystal substrate and ZnO:N film showed good rectification. Also, ultraviolet radiation and visible light were emitted from this junction under a forward bias at room temperature. It is therefore thought that ZnO:N films have good crystallinity and that doped nitrogen atoms play a role as acceptors in ZnO:N films to form a good pn junction. From these phenomena and the excitation intensity dependency of PL spectra, emissions at 3.334 and 3.31 eV were assigned to neutral acceptor-bound exciton (A⁰X) emission and a donor-acceptor pair (DAP) emission due to doped nitrogen, respectively.     

Femtosecond Third-Order Optical Nonlinearity of Au：Bi203 Nanocomposite Films

Ultrafast third-order optical nonlinearities of the as-deposited and annealed Au：Bi2O3 nanocomposite films deposited by magnetron cosputtering are investigated by using femtosecond time-resolved optical Kerr effect （OKE） and pump probe techniques. The third-order optical nonlinear susceptibility is estimated to be 2.6Ф×10^- 10 esu and 1.8 × 10.9 esu at wavelength of 800nm, for the as-deposited and the annealed film, respectively. The OKE signal of the as-deposited film is nearly temporally symmetrical with a peak centred at zero delay time, which indicates the dominant contribution from intraband transition of conduction electrons. For the annealed film, the existence of a decay process in OKE signal implies the important contribution of hot electrons. These characteristics are in agreement with the hot electron dynamics observed in pump probe measurement.     

Characterization and aging effect study of nitrogen-doped ZnO nanofilm

The influence of sputtering and annealing conditions and aging effect on properties of sputtered ZnO:N thin films were investigated. Achieved results confirmed a planar growth of nitrogen-doped ZnO film with a high uniform and smooth surface morphology. Incorporation of nitrogen in the ZnO films made new Raman shifts. X-ray diffraction spectra showed only the ZnO (0 0 2) diffraction peak, which was slightly shifted toward lower angels, compared to pure ZnO, which is the result of incorporating nitrogen in the ZnO films. The amount of this shift was proportional to N concentration. In addition, annealed samples showed better crystallinity with lower shift due to dramatically reduction of N atoms during the annealing. The Hall effect measurements exhibited p-type behaviour on annealed ZnO:N thin films while the un-annealed samples showed n-type conductivity. Aging effect studies demonstrated that the N content of thin films decreased dramatically as time passed. The reduction of N concentration in annealed samples was lower than un-annealed ones after 6 months.     

Induction of p-type conduction in sputtered deposited Al-N codoped ZnO thin films

Al and N codoped ZnO thin films were grown on n-Si (100) substrate by sputtering technique. Hall effect measurements of as-grown films exhibited n-type conduction, however 500 °C Ar annealed codoped films showed p-type conductivity with a hole concentration of 9.9 × 10¹⁶ cm^− 3, resistivity of 15.95 Ω-cm and hole mobility of 3.95 cm²/Vs, respectively. Codoped ZnO thin films were found to be highly c-axis oriented with good crystal quality. A neutral acceptor-bound exciton and donor-acceptor-pair emissions that appeared at room temperature photoluminescence measurement verify p-type conduction in Al and N codoped ZnO film. The current-voltage characteristics of p-n heterojunction evidently showed a diode like rectifying behaviour.     

Vacuum Ultraviolet Excited Photoluminescence Properties of Novel Na3Y9O3（BO3）8：Tb^3＋ Phosphor

The novel vacuum ultraviolet （VUV） excited Na3 Y9O3 （BO3）8：Tb^3＋ （NYOB：Tb^3＋） green phosphor is prepared. Strong VUV photoluminescence and high quenching concentration of Tb^3＋ （20 wt%） are observed in NYOB： Tb^3＋ and the strong emission are correlated with the unique layer-type structure of NYOB. All the characteristic 4 f - 5d transitions of Tb^3＋ and the host absorption band in VUV region are identified in the excitation spectrum. Based on the results, the energy levels scheme of Tb^3＋ in NYOB：Tb^3＋ is first established. This newly developed NYOB：Tb^3＋ phosphor shows excellent optical properties when compared with the commercial Zn2SiO4：Mn^2＋ and would be a potential VUV-excited green phosphor.     

离子束增强沉积制备p型氧化锌薄膜及其机理研究

采用离子束增强沉积方法在Si和SiO₂/Si衬底上制备In-N共掺杂ZnO薄膜(INZO)，溅射靶是用ZnO和2 atm% In₂O₃粉体均匀混合并压制而成，在氩离子溅射ZnO靶的同时，氮、氩混合离子束垂直注入沉积的薄膜.实验结果显示INZO薄膜具有(002)的择优取向，并且为p型导电，电阻率最低为0.9Ωcm.薄膜在氮气、氧气气氛下退火，对薄膜的结构和电学特性与成膜和退火条件的关系进行了分析. 关键词： 氧化锌薄膜 p型掺杂 离子束增强沉积     

Epitaxial Properties of Co-Doped ZnO Thin Films Grown by Plasma Assisted Molecular Beam Epitaxy

High quality Co-doped ZnO thin films are grown on single crystalline Al2O3（0001） and ZnO（0001） substrates by oxygen plasma assisted molecular beam epitaxy at a relatively lower substrate temperature of 450℃. The epitaxial conditions are examined with in-situ reflection high energy electron diffraction （RHEED） and ex-situ high resolution x-ray diffraction （HRXRD）. The epitaxial thin films are single crystal at film thickness smaller than 500nm and nominal concentration of Co dopant up to 20%. It is indicated that the Co cation is incorporated into the ZnO matrix as Co^2＋ substituting Zn^2＋ ions. Atomic force microscopy shows smooth surfaces with rms roughness of 1.9 nm. Room-temperature magnetization measurements reveal that the Co-doped ZnO thin films are ferromagnetic with Curie temperatures Tc above room temperature.     

Ferroelectric Properties of Bi3.25La0.75Ti3O12 Thin Films Crystallized inDifferent N2/O2 Ambients

Bi3.25La0.75 Ti3O12 （BLT） ferroelectric thin films are deposited by sol-gel method and annealed for crystallizaion in total l eccm N2/02 mixed gas with various ratio at 750℃ for 30rain. The effect of crystallization ambient on the structural and ferroelectric properties of the BLT films is studied. The growth direction and grain size of BLT film are revealed to affect ferroeleetric properties. Alter the BLT film is annealed in 20%O2, the largest P~ value is obtained, which is ascribed to an increase of random orientation and large grain size. The fatigue property is improved with the concentration of oxygen in the ambient increasing, which is ascribed to annealing in the ambient with high concentrated oxygen adequately decreasing the defects related to lack of oxygen.     

Comment on `Electronic Properties of Red P-Type Tl2S5 Single Crystals'

Recently, Gamal et al. [Chin. Phys. Lett. 22 (2005) 1530] reported the results of electrical conductivity, Hall effect and thermoelectric measurements on p-type Tl₂S₅ single crystals. From the experimental data for the temperature dependence of differential thermoelectric power, Gamal et al. determined thevalues of 2.66×10^-41kg and 2.50×10^-41kg, respectively, for the effective masses of electrons and holes in p-type Tl₂S₅, which are about ten orders of magnitude smaller than the free electron mass (9.11×10^-31kg). We argue that the anomalously small values obtained for the effective mass of chargecarriers in Tl₂S₅ have no physical significance.     

非掺杂ZnO薄膜中紫外与绿色发光中心

用直流反应溅射方法在硅衬底上淀积了ZnO薄膜,测量它们的光致发光(PL)光谱,观察到两个发光峰,峰值能量分别为3.18(紫外峰,UV)和2.38eV(绿峰).样品用不同温度分别在氧气、氮气和空气中热处理后,测量了PL光谱中绿峰和紫外峰强度随热处理温度和气氛的变化,同时比较了用FP-LMT方法计算的ZnO中几种本征缺陷的能级位置.根据实验和能级计算的结果,推测出ZnO薄膜中的紫外峰与ZnO带边激子跃迁有关,而绿色发光主要来源于导带底到氧错位缺陷(O_Zn)能级的跃迁,而不是通常认为的氧空 关键词： ZnO薄膜 热处理 光致发光光谱 缺陷能级     

Improvement of electrical and optical properties of Ga and N co-doped p-type ZnO thin films with thermal treatment

Ga and N co-doped p-type ZnO thin films were epitaxially grown on sapphire substrate using magnetron sputtering technique. The process of synthesized Ga and N co-doped ZnO films was performed in ambient gas of N₂O. Hall measurement shows a significant improvement of p-type characteristics with rapid thermal annealing (RTA) process in N₂ gas flow, where more N acceptors are activated. The film rapid thermal annealed at 900 °C in N₂ ambient revealed the highest carrier concentration of 9.36 × 10¹⁹ cm⁻³ and lowest resistivity of 1.39 × 10⁻¹ Ω cm. In room and low temperature photoluminescence measurements of the as grown and RTA treated film, donor acceptor pair emission and exciton bound to acceptor recombination at 3.25 and 3.357 eV, respectively, were observed.     

Realization of Ultraviolet Electroluminescence from ZnO Homojunction Fabricated on Silicon Substrate with p-Type ZnO:N Layer Formed by Radical N2O Doping

ZnO homojunction light-emitting diodes are fabricated on Si（100） substrates by plasma assisted metal organic chemical vapour deposition. A p-type layer of nitrogen-doped ZnO film is formed using radical N2O as the acceptor precursor. The n-type ZnO layer is composed of un-doped ZnO film. The device exhibits desirable rectifying behaviour with a turn-on voltage of 3.3 V and a reverse breakdown voltage higher than 6 V. Distinct electrolumineseence emissions centred at 395nm and 490nm are detected from this device at forward current higher than 20mA at room temperature.     

Effect of annealing temperature and annealing atmosphere on the structure and optical properties of ZnO thin films on sapphire (0 0 0 1) substrates by magnetron sputtering

ZnO thin films were epitaxially grown on sapphire (0 0 0 1) substrates by radio frequency magnetron sputtering. ZnO thin films were then annealed at different temperatures in air and in various atmospheres at 800 °C, respectively. The effect of the annealing temperature and annealing atmosphere on the structure and optical properties of ZnO thin films are investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL). A strong (0 0 2) diffraction peak of all ZnO thin films shows a polycrystalline hexagonal wurtzite structure and high preferential c-axis orientation. XRD and AFM results reveal that the better structural quality, relatively smaller tensile stress, smooth, uniform of ZnO thin films were obtained when annealed at 800 °C in N₂. Room temperature PL spectrum can be divided into the UV emission and the Visible broad band emission. The UV emission can be attributed to the near band edge emission (NBE) and the Visible broad band emission can be ascribed to the deep level emissions (DLE). By analyzing our experimental results, we recommend that the deep-level emission correspond to oxygen vacancy (V_O) and interstitial oxygen (O_i). The biggest ratio of the PL intensity of UV emission to that of visible emission (I_NBE/I_DLE) is observed from ZnO thin films annealed at 800 °C in N₂. Therefore, we suggest that annealing temperature of 800 °C and annealing atmosphere of N₂ are the most suitable annealing conditions for obtaining high quality ZnO thin films with good luminescence performance.