Defects, stress and abnormal shift of the (0 0 2) diffraction peak for Li-doped ZnO films

The effect of changes in Li content on the structural property of sol-gel Li-doped ZnO films was investigated in this study. The observed changes of the Li incorporation-induced strain along c-axis are closely related to the different ratios between the concentrations of Li interstitials (Li_i) and Li substituting for Zn (Li_Zn) in the films. According to the observed results from X-ray diffraction (XRD) and photoluminescence measurements, we found that the domination of the dissociative mechanism in the Li-doped ZnO films led to transformation from Li_Zn to Li_i, involving the formation of Zn vacancies (V_Zn). In addition, the interaction between these defects (that is, Li_Zn, Li_i, V_Zn and oxygen vacancy) and the crystal structure may lead to the abnormal shift of the (0 0 2) diffraction peak position determined from XRD measurements.     

Fabrication of Sb-doped p-type ZnO thin films by pulsed laser deposition

p-Type ZnO thin films have been realized via monodoping antimony (Sb) acceptor by using pulsed laser deposition. The obtained films with the best electrical properties show a hole concentration in the order of 10¹⁸ cm⁻³ and resistivity in the range of 2-4 Ω cm. X-ray diffraction measurements revealed that all the films possessed a good crystallinity with (0 0 2)-preferred orientation. Guided by X-ray photoemission spectroscopy analysis and a model for large-sized-mismatched group-V dopant in ZnO, an Sb_Zn-2V_Zn complex is believed to be the most possible acceptor in the Sb-doped p-type ZnO thin films.     

First-principles calculation on p-type conduction of (Sb,N) codoping in ZnO

Based on first-principles calculations, (Sb, N) codoped ZnO are investigated. We find that Sb_Zn–4N_O have lower formation energy and can form p-type conduction with smaller hole effective mass. In comparation to monodoping of Sb, Sb_Zn–4N_O complex can form better p-type conductivity than Sb_Zn–2V_Zn, which may be strongly compensated by Sb_Zn defect and result in a decrease of p-type conduction. So we inferred that (Sb, N) codoping in ZnO under O-poor condition should be a realizable candidate of p-type conduction.     

Effect of substrate temperature on the morphology, structural and optical properties of Zn1−xCoxO thin films

Zn_1−xCo_xO thin films with c-axis preferred orientation were deposited on sapphire (0 0 0 1) by pulsed laser deposition (PLD) technique at different substrate temperatures in an oxygen-deficient ambient. The effect of substrate temperature on the microstructure, morphology and the optical properties of the Zn_1−xCo_xO thin films was studied by means of X-ray diffraction (XRD), atomic force microscopy (AFM), UV-visible-NIR spectrophotometer, fluorescence spectrophotometer. The results showed that the crystallization of the films was promoted as substrate temperature rose. The structure of the samples was not distorted by the Co incorporating into ZnO lattice. The surface roughness of all samples decreased as substrate temperature increased. The Co concentration in the film was higher than in the target. Emission peak near band edge emission of ZnO from the PL spectra of the all samples was quenched because the dopant complexes acted as non-radiative centers. While three emission bands located at 409 nm (3.03 eV), 496 nm (2.5 eV) and 513 nm (2.4 eV) were, respectively, observed from the PL spectra of the four samples. The three emission bands were in relation to Zn interstitials, Zn vacancies and the complex of V_O and Zn_i (V_OZn_i). The quantity of the Zn interstitials maintained invariable basically, while the quantity of the V_OZn_i slightly decreased as substrate temperature increased.     

Evolutions of defects and blue–green emissions in ZnO microwhiskers fabricated by vapor-phase transport

The corresponding evolutions of morphologies, defect-states and the PL properties have been employed to explore the defect-origins of visible emissions and growth mechanisms of microstructured ZnO. ZnO microtube and microrod whiskers were fabricated by non-catalytic vapor-phase transport using ZnO and graphite powders in air. The microstructures of the samples were studied in detail based on scanning electron microscopy (SEM), x-ray diffraction (XRD), energy-dispersive x-ray spectroscopy (EDX), and electron paramagnetic resonance (EPR). The main PL emission bands evolve from blue to green, which corresponds to that the main defect-states change from Zn interstitials (Zn_i) to O vacancies (V_O). The formation of Zn_i under the high temperature zinc-rich vapor environment is crucial both for the blue emission and for the formation of the microtubes.     

Effects of micro-additions on structures and properties of rapidly solidified Sn-10% Sb alloy

Structure, electrical resistivity, hardness, internal friction and elastic modulus of Sn-10% Sb and Sn₈₉Sb₁₀M₁ (M₁ = Ag, Cu, Zn and Pb) alloys have been investigated. No obvious change on the electrical resistivity value was found at 293 °K of a Sn-10% Sb alloy by adding Zn and Cu, but extreme changes occurred after adding Ag and Pb. The elastic modulus, internal friction, hardness and thermal diffusivity values are greatly affected by adding the micro-additions to a Sn-10% Sb rapidly solidified alloy. It is also interesting to note that Ledbetter's theoretical values of μ/E are in good agreement with the experimental results. The rapidly solidified alloys Sn₉₀Sb₁₀ and Sn₈₉Sb₁₀Ag₁ have good properties as toxic-free lead solder alloys for high-temperature applications and good mechanical properties such as under the hood in the automobile and avionics systems. Also, the rapidly solidified alloys Sn₈₉Sb₁₀Zn₁, Sn₈₉Sb₁₀Cu₁ and Sn₈₉Sb₁₀Pb₁ have good properties as bearing materials.     

Electrical and optical spectroscopy on ZnO:Co thin films

Magnetic oxide semiconductors, for example the highly transparent and intrinsically n-type conducting zinc oxide doped with the 3d transition metal Co (ZnO:Co), are promising for the emerging field of spintronics [1]. We investigated n-conducting ZnO:Co thin films with a Co content of nominal 0.02, 0.20, or 2.00 at. %. The substitution of Co cations in the tetrahedral sites of wurtzite ZnO with Zn was confirmed at low temperature by the 1.877 eV photoluminescence between crystal field split d-levels of Co²⁺ (d⁷) ions. Based on theoretical studies, it is predicted that the formation of electron levels with zinc interstitials (I_Zn) or hole levels with zinc vacancies (V_Zn) is necessary to induce ferromagnetism, whereas the formation of electron levels with oxygen vacancies (V_O) is detrimental for ferromagnetism in ZnO:Co [2]. Cobalt generates a hole level in ZnO [3]. We investigated the generation of electron levels in n-conducting ZnO:Co in dependence on the Co content by means of deep level transient spectroscopy (DLTS). However, because of the ambiguous categorization of deep defects in n-conducting ZnO (V_O, I_Zn), an optimization of defect-related ferromagnetism in ZnO:Co is not possible at the moment. PACS 78.30.Fs; 91.60.Ed; 91.60.Mk     

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     

Al和Sb共掺对ZnO有序阵列薄膜的结构和光学性能的影响

采用水热合成法在预先生长的ZnO种子层的玻璃衬底上制备出Al和Sb共掺ZnO纳米棒有序阵列薄膜. 通过X射线衍射、扫描电镜、透射电镜和选区电子衍射分析表明:所制备的薄膜由垂直于ZnO种子层的纳米棒组成, 呈单晶六角纤锌矿ZnO结构, 且沿[001]方向择优生长, 纳米棒的平均直径和长度分别为27.8 nm和1.02 μm. Al和Sb共掺ZnO纳米棒有序阵列薄膜的拉曼散射分析表明:相对于未掺杂ZnO薄膜的拉曼振动峰(580 cm^-1), Al和Sb共掺ZnO阵列薄膜的E₁(LO)振动模式存在拉曼位移. 当Al和Sb的掺杂量为3.0at%,4.0at%,5.0at%,6.0at%时, Al和Sb共掺ZnO阵列薄膜的拉曼振动峰的位移量分别为3,10,14,12 cm^-1. E₁ (LO) 振动模式位移是由Al和Sb掺杂ZnO产生的缺陷引起的. 室温光致发光结果表明:掺杂Al和Sb后, ZnO薄膜在545 nm处的发光强度减小,在414 nm处的发光强度增加. 这是由于掺杂Al和Sb后, ZnO薄膜中Zn_i缺陷增加, O_i缺陷减少引起的. 关键词： Al和Sb共掺ZnO薄膜 纳米棒有序阵列 结构表征 拉曼散射     

Dopant activation in Sb-implanted relaxed Si1−xGex alloy layers grown on compositionally graded buffers

Supersaturated solid solutions of substitutional, electrically active Sb have been obtained by ion implantation of relaxed epitaxial Si_1?xGe_x alloy layers grown on compositionally graded buffers. Substitutional and nonsubstitutional Sb fractions in relaxed Si_0.85Ge_0.15, Si_0.65Ge_0.35 and Si_0.50Ge_0.50 alloy layers implanted to a dose of 5×10¹⁵ Sb cm^?2 and annealed isothermally at temperatures ranging from 400 to 850°C have been studied by Rutherford backscattering/channeling, transmission electron microscopy and Hall-effect and sheet resistivity measurements. A supersaturated solution of Sb corresponding to a peak carrier concentration of 4×10²⁰ cm^?3 and an electrically active fraction of 40% of the implanted dose is observed by Hall measurements for the case of Si_0.85Ge_0.15 and Si_0.65Ge_0.35 alloys annealed at 550°C.     

Cluster generation under pulsed laser ablation of zinc oxide

Neutral and cationic Zn _n O _m clusters of various stoichiometry have been produced by nanosecond laser ablation of ZnO in vacuum and investigated by time-of-flight mass spectrometry. Particular attention was paid to the effect of laser wavelength (in the range from near-IR to UV) on cluster composition. Under 193-nm laser ablation, the charged clusters are essentially substoichiometric with Zn_nO_n-1⁺\mathrm{Zn}_{n}\mathrm{O}_{n-1}^{+} and Zn_nO_n-3⁺\mathrm{Zn}_{n}\mathrm{O}_{n-3}^{+} being the most abundant series. Both sub- and stoichiometric cationic clusters are generated in abundance at 532- and 1064-nm ablation whose composition depends on the cluster size. The reactivity of small stoichiometric Zn_nO_n⁺\mathrm{Zn}_{n}\mathrm{O}_{n}^{+} clusters (n<11) toward hydrogen is found to be high, while oxygen-deficient species are less reactive. The neutral plume particles are mainly stoichiometric with Zn₄O₄ tetramer being a magic cluster. It is suggested that the Zn₄O₄ loss is the dominant fragmentation channel of large zinc oxide clusters upon electron impact. Plume expansion conditions under ZnO ablation with visible and IR laser pulses are shown to be favorable for stoichiometric cluster formation.     

Vacancy defects in (Zn, Mn)O

We have used positron annihilation spectroscopy to study the vacancy defects in (Zn, Mn)O crystals grown by chemical vapor transport (CVT). Our results show that Zn vacancies are present in both as-grown and high temperature annealed ZnO and Zn_0.985Mn_0.015O. In addition, we observe O vacancies in ZnO with no Mn. After annealing in O₂ at 1000 C, there is no change in the vacancy distribution in ZnO, while the Zn vacancy concentration increases by an order of magnitude in Zn_0.985Mn_0.015O.     

Structural phase transition behaviour of ZnaSb3 and its substitutional compounds （Zn0.98M0.02）4Sb3 （M = Al,Ga and In） at low temperatures

Structural phase transitions of Zn4Sb3 and its substitutional compounds (Zn0.98M0.02)4Sb3 (M = Al, Ga and In) are investigated by electrical transport measurement and differential scanning calorimetry below room temperature. The results indicate that both β→α and α→α′ phase transitions of Zn4Sb3 are reversible and exothermic processes, which may be explained as that both the transitions originate from the ordering of the disordered interstitial Zn and vacancies in regular sizes. The derived activation energies of β→α and α→α′ phase transition processes for Zn4Sb3 are E1 = 3.9 eV and E2 = 4.1 eV, respectively. Although no remarkable influence on activation energy E2 is observed after Al doping, Al substitution for Zn causes E1 to increase to 4.6 eV, implying its suppression of βα transition to a great extent. Moreover, it is found that both βα and αα′ transitions are completely prohibited by substitution of either In or Ga for Zn in Zn4Sb3. The underlying mechanisms for these phenomena are discussed.     

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     

Electrical properties of Cd,Zn and S ion-implanted layers in GaAs

The electrical properties of cadmium, zinc, and sulfur ion-implanted layers in gallium arsenide have been measured by the van der Pauw-Hall technique. Ion implantation was performed with the substrates held at room temperature. The dependence of sheet resistivity, surface carrier concentration, and mobility on ion dose and on post-implantation anneal temperature was determined. In the case of 60 keV Cd⁺ ions implanted into n-type substrates, a measurable p-type layer resulted when samples were annealed for 10 minutes at a temperature in the range 600—900°C. After annealing at 300—900°C for 10 minutes, 100 per cent electrical activity of the Cd ions resulted for ion doses ≤ 10¹⁴/cm².

The properties of p-type layers produced by implantation of 85 keV Zn⁺ ions were similar to those of the 60 keV cadmium-implanted layers, in that no measurable p-type behavior was observed in samples annealed below a relatively high temperature. However, in samples implanted with 20 keV Zn⁺ ions a p-type layer was observed after annealing for 10 minutes at temperatures as low as 300°C.

Implantation of sulfur ions into p-type GaAs substrates at room temperature resulted in the formation of a high resistivity n-type layer, evcn before any annealing was performed. Annealing at temperatures up to 200°C or above 600°C lowered the resistivity of the layer, while annealing in the range 300—500°C eliminated the n-type layer.     

Structure distortion, optical and electrical properties of ZnO thin films co-doped with Al and Sb by so--gel spin coating

ZnO thin films co-doped with Al and Sb with different concentrations and a fixed molar ratio of AlCl₃ to SbCl₃ at 1:2, are prepared by a sol--gel spin-coating method on glass annealed at 550 ℃ for 2 h in air. The x-ray diffraction results confirm that the ZnO thin films co-doped with Al and Sb are of wurtzite hexagonal ZnO with a very small distortion, and the biaxial stresses are 1.03×10⁸, 3.26×10⁸, 5.23×10⁸, and 6.97×10⁸ Pa, corresponding to those of the ZnO thin films co-doped with Al and Sb in concentrations of 1.5, 3.0, 4.5, 6.0 at% respectively. The optical properties reveal that the ZnO thin films co-doped with Al and Sb have obviously enhanced transmittance in the visible region. The electrical properties show that ZnO thin film co-doped with Al and Sb in a concentration of 1.5 at% has a lowest resistivity of 2.5Ω·cm.     

离子注入Zn的Si(001)基片热氧化制备纳米ZnO团簇及其生长行为研究

采用离子注入技术将Zn离子注入Si（001）基片,并在大气环境下加热氧化制备了ZnO纳米团簇.利用电子探针、薄膜X射线衍射仪、原子力显微镜和透射电子显微镜,对注入和热氧化后的薄膜成分、表面形貌和微观结构进行表征,探讨了热氧化温度以及注入剂量对纳米ZnO团簇的成核过程及生长行为的影响.结果表明,Zn离子注入到Si基片表面后形成了Zn纳米团簇,热氧化过程中Zn离子向表面扩散,在表面SiO₂非晶层和Si基片多晶区的界面处形成纳米团簇.热氧化温度是影响ZnO纳米团簇结晶质量的一个重要参数.随着热氧化温度的升高,金属Zn的衍射峰强度逐渐变弱并消失,而ZnO的（101）衍射峰强度逐渐增强.当热氧化温度高于800 ℃以后,ZnO与SiO₂之间开始发生化学反应形成Zn₂SiO₄. 关键词： ZnO纳米团簇 离子注入 微观结构 形貌分析     

Effects of a Cu-contained compound on the microstructures and thermoelectric properties of Zn–Sb based alloys

Zn–Sb based alloys with Cu₂Sb addition were prepared using spark plasma sintering technique and the effects of a Cu-contained intermetallic phase on the microstructures and thermoelectric properties were examined. Rietveld refinement reveals that there are many phases in the alloys, which involve β-Zn₄Sb₃, a major phase ZnSb, a small amount of an intermetallic compound Cu₅Zn₈ and unidentified impurity phases, the quantities of ZnSb and Cu₅Zn₈ increase from 67.3 wt.% to 91.8 wt.% and 0–4.3 wt.% with Cu₂Sb additive increasing, respectively. The ZnSb plays a fundamental role in controlling the thermoelectric properties, and Cu₅Zn₈ is of great significance to optimize the transport properties. The maximum thermoelectric figure of merit ZT of 0.72 is obtained for the alloy (Cu₂Sb)_0.05–(Zn₄Sb₃)_0.95 at 654 K, which is 0.25 higher than that of undoped β-Zn₄Sb₃ at the same conditions. Therefore, we conclude that a proper addition of Cu₂Sb can contribute to the improvement of thermoelectric properties of Zn–Sb based alloys.     

Ion beam synthesis and carrier dynamics of ZnO nanoparticles embedded in a SiO2 matrix

Zinc oxide (ZnO) nanostructures have been synthesized by the implantation of ZnO molecular ions into SiO₂ followed by high temperature thermal annealing. 35 keV ZnO^? ions were implanted to a fluence of 5×10¹⁶ ions/cm² into SiO₂ at room temperature (RT). The implanted sample was annealed in an oxygen environment to allow the growth of ZnO precipitates. In the as-implanted sample, Zn nanoparticles up to 4.5 nm in diameter were observed and were distributed throughout the implanted depth in the SiO₂. The highest concentration of Zn from the implantation was at a depth of 25 nm. During annealing, Zn diffused into the substrate and combined with oxygen to form ZnO. ZnO nanostructures thus formed had diameters up to 8 nm, embedded in SiO₂. Donor-bound exciton (D, X), acceptor-bound exciton (A, X), and donor–acceptor-pair (DAP) transitions were observed in low temperature photoluminescence (PL) measurements on an annealed sample. RT-PL measurement showed band-edge emission in the ultraviolet region with a full width at half maximum of 121 meV. Time-resolved PL measurements performed at 4 K revealed an excitonic lifetime of 160 ps.     

Atomic layer deposition and characterization of Ga-doped ZnO thin films

Low-resistivity n-type ZnO thin films were grown by atomic layer deposition (ALD) using diethylzinc (DEZ) and H₂O as Zn and O precursors. ZnO thin films were grown on c-plane sapphire (c- Al₂O₃) substrates at 300 C. For undoped ZnO thin films, it was found that the intensity of ZnO () reflection peak increased and the electron concentration increased from 6.8×10¹⁸ to 1.1×10²⁰ cm⁻³ with the increase of DEZ flow rate, which indicates the increase of O vacancies () and/or Zn interstitials (Zn_i). Ga-doping was performed under Zn-rich growth conditions using triethylgallium (TEG) as Ga precursor. The resistivity of 8.0×10⁻⁴ Ω cm was achieved at the TEG flow rate of 0.24 μmol/min.