第3l卷第2期 发 光 学 报 V0I.31 No.2 2010年4月 CHINESE JOURNAL 0F LUMINESCENCE Apr.,2010 Article ID:1000-7032(2010)02—0189-O5 ZnO Films Grown by the Vapor Transport Method L1N Xiu—zhu ,LI Jing , ,WU Qi—hui。 (1.Department ofphysics,Xiamen University,Xiamen 361005,China; 2.Pen—Tung Sah Micro—Nano Technology Research Center,Xiamen University,Xiamen 361005,China 3.Departemnt ofPhysics,La Trobe University,Bundoora 3086,VIC,Australia) Abstract:The characterizations of surface morphologies,crystal structures,and optical properties of the ZnO films prepared by a vapour—phase technique on different substrates were performed in this study.Scanning electron micro— scopy(SEM、data showed that larger ZnO particles are formed on the Au—covered Si substrates than those on Si sub— strates.X—rav diffraction(XRD)results indicated that hexagonal wurtzite ZnO iflms are grown on both Si(1 1 1)and Si(100)substrates though they present different diffraction peaks with hexagonal wurtzite structure,while appears no sDhalerite strueture.The ZnO films prepared on Au—coated Si substrates prefer to grow along with c—axis orientation. The PL sDectra reveal onlv a narrow strong UV emission peak at about 389 am(3.19 eV)in all the ZnO samples. Key words:ZnO;thin film;vapor transport;water vapor CLC number:0472.3;0482.31 PACS:78.55.Et PACC:3250F;7855 Document code:A Various fabrication techniques have been established 1 Intr0ducti0n for the growth of thin ZnO films and nanostructures, In recent years,ZnO,as a wide band gap semi・ such as the molecular beam epitaxy(MBE) , conductor,has attracted much attention on studying chemical vapor deposition ’7j, vapor—phase its growth mechanism and electrical and optoelec— rgowth[ ~ aqueous solution growth ll_。,elec— tronic properties due to a variety of applications in troehemical deposition_1 2_.carbonthermal evapora— electronic,photoelectronic and spintronic devices. tion㈣lfux growth and template-based synthesis[14I.. ZnO has a stable hexagonal wurtzite structure in the We synthesized ZnO films using a vapor transfer me— space group P63 mc with lattice spacing a=0.325 thod.The Zn powders with high purity and H2 O vapor nm and c=0.52 1 nm.Its large exciton binding were employed as the sources.After heated at above energy(60 meV),which is much greater than the 800℃and below 1 180 oC.the Zn powders will be thermal energy at room temperature(RT),makes it transferred to gas phase Zn vapor,thus the reaction a promising candidate for applications in blue—UV equation can be written as following, light emission and RT UV lasing….Furthermore, Zn(g)+H2O(g) <l 18O℃ ZnO(s)+H2(g) ZnO can be used as a highly transparent electrode Different nanostruetures of ZnO films were syn— material for solar cells【 a phosphor material for ,thesized on different substrates.Morphologies of the converting radiation to visible light at low volta— grown ZnO films were imaged by scanning electron ges( a piezoelectric material in mechanical trans— .microscopy(SEM).Films’crystal structures and ducers and a gas—detection material for microsensors optical properties were then characterized by X—ray due to its unique electronic properties,piezoelectri_ diffraction(XRD)and phot0luminescence(PL) city,and sudace chemistry sensitive to environment. specturm,respectively. Received date:2009-1 1-03;Revised date:2010-01—15 Foundation item:Project suppoaed by National Natural Science Foundation of China(20603028) Biography:LIN Xiu.zhu,born in 1984,female,F ̄ian Province.Her work focuses on optoelectronic materials E—mail:xzhlin@XnlU.edu.cn :Corresponding Author;E-mail:lijing@XmH.edu.cFI,Tel:(0592)2181340 发 光 学 报 第31卷 2 Experiments The reactions of the vapor—phase growth took 800℃for 1 h with the flow of nitrogen gas mixed H2O vapor;finally,the furnace was switched off and the samples were cooled down to RT. The morphologies of the nanostructures were place in a large quartz tube horizontally lain down in a rapid thermal furnace.For the purpose of control— ling the stable pressure and the high eficifent use of the Zn powders during ZnO synthesis,another much smaller quartz tube placed in the large quartz tube characterized by using a LEO一1530FE—SEM.The crystal structures were analyzed by XRD within the 20 range of 20。~80。at a scan rate of 0.0167。/ step,using PANalytical X’pert PRO X—ray diffractor was used to create a zinc—rich environment during the growth of ZnO.Fig.1 shows the schematic illus— tration of the furnace including a horizontal quartz tube of about 2 m in length and 20 cm in diameter, and a smaller quartz tube of 15 cm in length and 3 cm in diameter located in the middle of the bigger quartz tube.The huge difference in size between these two tubes will provide a stable Zn vapor pres— sure during ZnO deposition.The Zn powders and the substrates were placed with a distance of about 0.5 cm in the smaller quartz tube.In this experiment, mi ̄or—polished p-type silicon wafers of 25 mm in diameter,such as Si(111)and Si(100),cleaned by acetone and alcohol,were used as substrates. SiO2/Si(1OO)surface was prepared by oxidizing the clean Si(100)wafer with the alternation of dry and wet O2 to form about 500 nm SiO2 layer.The Au covered Si(100)and SiO2/Si(100)substrates were prepared by depositing a 200 nm thick layer of Au on the cleaned Si(100)and SiO2/Si(100)wafers using RF—sputtering(JC500—3/D)with a gold traget. ・--------- 'pGas Uowb 一ti。,,,’~.,’/ Small buanz btu 三}a;i z 穹【J / o 。 Fig.1 The schematic illustration of the vapor—growth system with a large hofizontM qua ̄z tube placed in a furnace and a smaller quartz tube inside the big quanz tube The synthesis procedures were carried out in the following steps:first,nitrogen gas was flown through the quartz tubes for 1 h in order to drive away the impure gases;second,the furnace tempe— rature was elevated to 800 oC in 1 h with nitrogen gas flying;third,the temperature was maintained at with Cu/Mo radiation source.PL measurements were taken at RT using a KrF excimer laser line of 248 nm as the excitation source by a Hitachi F-4500 spectrophotometer. 3 Results and Discussion The morphologies of ZnO films deposited on dif- ferent substrates at 800 oC are shown in Fig.2.It is ofund that the ZnO films grown on Si(111)[Fig.2 (a)]and Si(100)[Fig.2(b)]subsrtates are more smooth.Strip shape ZnO particles with different si- zes and orientations can be observed.This implies that the growth of ZnO has no any dominate direction on the Si(111)and Si(100)substrates in this study. For ZnO grown on Au・coated Si(100)and SiO2/Si (100)substrates,circle—like-on-top nanoparticles call be found in Fig.2(c)and(d).The size is baout 10 to 200 nnl in diameter.The nanoparticles labeled as M are fiat,labeled as N are gyroidal,and the extremely bright spot labeled as H can be assigned Fig.2 The SEM images of ZnO films grown on(a)Si (11 1),(b)Si(100),(c)Au-coated Si(100), and (d)Au—coated SiO2/Si(100)substrates at 800 ℃for 1 h. 第2期 LIN Xiu.zhu,et al:ZnO Films Grown by the Vapor Transport Method 191 as a nucleating clusters.By comparing the SEM images in Fig.2,it can be found that the average around 34。assigned to the(002)plane diffraction peak besides Au(111),(200)and(220)peaks at around 38。,45。,and 65。,respectively.This re— sult indicates that the ZnO films grown with Au ca- size of the nanopartieles in Fig.2(c)and(d)is larger than that in Fig.2(a)and(b).This suggests that the ZnO growth rate on the Au covered Si sub— strates is faster than that on the Si substrates due to the catalysis effect of Au. The influence of the substrate on the ZnO crys- talysis are highly orientated in c—axis along[0001] direction.Unfortunately,the use of metal catalyst f0r the growth of ZnO films makes the presence of unwanted impurities inevitable.Additionally,the appearances of Si related diffraction peaks are be‘ tal structure is depicted in Fig.3.It is clear that substrate plays an important role in determining the crysta1 strueture of the ZnO films.The films deposi— lieved from Si substrates.The variations in crystal structure among those samples on different substrates might be due to the different surface diffusion ener— gies,and atomic structure of these substrates,which affect the surface diffusion and adsorption of the reae— ted on Si(1 1 1)has a polycrystalline structure with a f 002)preferred orientation.Secondary peaks pre— sent are(100),(101),(102),(110)and (103).All these diffraction peaks can be indexed to a Dure hexagonal wurtzite ZnO structure.The film tants(e.g.Zn and H2O)as well as their reaction rate.More detailed study is needed to be performed in order to clearly understand the substrate inf- luences on the crystal structure. deposited on Si(1013)has two dominate ZnO peaks: (002)and(200).The ZnO films grown on the Au covered Si substrates have the most dominate peak at The optical properties of aII synthesized ZnO 20/(。) 20/(。) 20/(。) 20/(。) Fig.3 The XRD patterns。fZnO films grown。n(a)si(1it),(b)si(1oo),(c)Au-eoated Si(1O0),and(d)Au—c。a ed SiO2/Si(100)substrates. samples are displayed by PL spectum fr seen in Fig・ 4、.Expect for the difference in peak intensity,it is ar0und 389 nm(3.19 eV)in wavelength.The UV emission band is attributed to a near band—edge ex— citonic transition of ZnO .While there is no green interesting to find that all RT PL spectra of the ZnO samples consist of only a narrow strong UV peak at emission peak,which is related to some deep level 192 发 光 学 报 第31卷 transition induced by defects,e.g.oxygen vacan— cies (e.g.single ionized oxygen vacancies)or impurities.Thus,ZnO synthesized through the vapor method in this study is highly crystalline with few defects and impurities. 4 Conclusion The ZnO films were synthesized by reaction of Zn vapor and H2 O vapor using a vapor—phase tech— nique on different substrates.Films’surface mor— phologies,crystal structures,and optical properties were investigated.The SEM data suggested that higher growth rate is found on the Au covered sub— strates.XRD studies indicated that the growth orien— tation of ZnO strongly depends on the substrates. ZnO films grown on Si(111)or Si(100)substrates presents different diffraction peaks in hexagonal wurtzite structure,while appears no sphalerite struc・ A/nm ture.The ZnO films grown on Au—coated Si sub・ Fig.4 Room—temperature PL spectrum of the ZnO films de— strates prefer to grow along c-axis orientation.The posited Oll(a)Si(111),(b)Si(100),(c)Au— PL spectra with showing only a narrow strong UV coated Si(100),and(d)Au—coated SiO2/Si(100) emission peak reveal few defects and impurities in substrates(d labeled as dotted line). the synthesized ZnO films. References: [1]Huang M H,Mao S,Feick H,et a1.Room—temperature ultraviolet nanowire nanolasers[J].Science,2001,292(5523): 1897.1899. [2]Morgan J H,Brodie D E.The preparation and some properties of transparent conducting ZnO for use in solar—cells[J]. Can. Phys.,1982,60(10):1387—1390. [3]Vanheusden K,Seager C H,Warren W L,et a1. 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[15]Zhang Y,Jja H B,Yu D P,et a1.Low—temperature growth and Raman scattering study of vertically Migned ZnO nanowires on Si substrate[J].App1.P .Lett.,2003,83(22):4631-4633. [16]Vanheusden K,Wa ̄en W L,Seager C H,et a1. Mechanisms behind green ph0toluminescence in ZnO phosphor powders [J]._,.App1.P, .,1996,79(10):7983—1990. 气相输运法制备ZnO薄膜 林秀珠 ,李 静 ,吴启辉 (1.厦门大学物理系,福建厦门361005; 2.厦门大学萨本栋微纳米技术研究中心,福建厦门361005 3.拉筹伯大学物理系,澳大利亚维多利亚本多拉3086) 摘要:运用气相输运技术在不同的衬底上制备ZnO薄膜,同时对这些ZnO薄膜的表面形貌、晶体结构和光 学特性进行表征。在扫描电子显微镜图像上可以看到,相比没有镀金的 衬底,ZnO纳米颗粒在镀金的Sj衬 底上的生长尺寸较大。x射线衍射测试结果表明,在Si(111)和si(100)衬底上生长的ZnO薄膜显示出不同 的六角纤锌矿结构的衍射峰,但没有出现立方闪锌矿ZnO结构的衍射峰。在镀金的si衬底上,ZnO薄膜生长 取向主要为c轴方向。此外,所有ZnO样品的光致发光谱上均只出现一个狭窄且强的紫外峰,约在389 nm (3.19 eV)波长处。 关键词:ZnO;薄膜;气相输运;水蒸气 中图分类号:0472.3;0482.31 PACS:78.55.Et PACC:3250F;7855 文献标识码:A 文章编号:1000-7032(2010)02-0189-05 收稿日期: 2009—11-03;修订日期:2010-01—15 基金项目: 国家自然科学基金(20603028)资助项目 作者简介: 林秀珠(1984一),女,福建福州人,主要从事光电子材料的研究。 E—mail:xzhlin@xmu.edu.cn 通讯联系人;E—mail:lijing@xmu edu.cn,Tel:(0592)2181340