1、第28卷第5期材料科學(xué)與工程學(xué)報(bào)Journal of M aterials Science & Engineering總第127期Oct . 20 10Vo l 28No 5Article ID: 1673 2812( 2010) 05 0688 05Structure of Ge Se Bi Films Prepared by Pulsed Laser DepositionPAN Rui kun1, 2 , ZANG Hao cun2 , LIN Chang gui2, TAO Hai zheng2 ,ZHAO Xiu jian2 , ZHANG Tian jin1( 1. School o

2、f Materials Science & Engineering, Hubei University, Wuhan 430062, China; 2. Key Laboratory of Silicate Materials Science & Engineering, Wuhan University of Technology, Ministry of Education, Wuhan 430070, China)AbstractAm orpho us ( GeSe2 ) 100- x Bix ( x = 0 12) f ilms w ere prepared by the pulsed

3、 laser deposition( PL D) technique. T he optical t ransmission spectra, absorptio n spectra and Ram an spectra o f the as depo sitedand annealed f ilms w er e m easured. T he short w av e absor ption edges of the film s w ere described using the no n direct transition model propo sed by T auc. The o

4、ptical band g aps ( Eg ) w ere determined. The T auc slopesoptcm- 1e/ 2V w- 1i/t2hincreasing Bi content. Eg decroepat sesfro m1. 94to1. 11eVdecrease f rom 486 to 178monotonously w ith increasing Bi content and incr eases more or less ( 0 240 meV) after annealing. Ramanspectra analy sis indicates tha

5、t adding Bi decreases the mean bond energy in the amo rphous films, w hich causedoptEg .the decrease ofT he therm al bleaching effect ( as much as 240 meV ) w as discussed in relation to thedecreasing diso rder in the g lass netw ork and the reduction in the mean bond energ y of the as deposit ed f

6、ilms, w hich w ere confir med by the bigg er T auc slopes and the Ram an spectra analysis, respectiv ely .Key words chalcogenides film s; optical Band gap; Ram an spectr aCLC number: T Q 171. 73+ 4Document Code: A脈沖激光沉積法制備 Ge Se Bi 硫系玻璃薄膜的結(jié)構(gòu)潘瑞琨1, 2 , 臧浩春2 , 林常規(guī)2 , 陶海征2, 趙修建2 , 章天金1( 1. 湖北大學(xué)材料科學(xué)與工程學(xué)院

7、, 湖北 武漢 430062; 2. 武漢理工大學(xué)硅酸鹽材料教育部重點(diǎn)實(shí)驗(yàn)室, 湖北 武漢 430070)采用脈沖激光沉積法制備了( GeSe2 ) 100- x Bix ( x = 0 12) 硫系玻璃薄膜。測(cè)量了薄膜摘要的光學(xué)透射譜、吸收譜和拉曼光譜。薄膜的光學(xué)短波吸收邊對(duì)應(yīng)于電子的間接帶間躍遷, 并由此計(jì)算出其光學(xué)帶隙。拉曼光譜分析表明Bi 含量的增加, 減小了玻璃的平均鍵能, 導(dǎo)致光學(xué)帶隙由 1. 94 eV 減小到 1. 11 eV。Tauc 斜率由 486 cm- 1/ 2 eV- 1/ 2 減小到 178 cm- 1/ 2 eV- 1/ 2 。退火過程中的熱漂白效應(yīng)減小了玻璃的結(jié)

8、構(gòu)無序性, 使得薄膜的光學(xué)帶隙和T auc 斜率相應(yīng)增大。 關(guān)鍵詞硫系玻璃薄膜; 光學(xué)帶隙; 拉曼光譜 materials for the applications in optical w aveguide devices. T he phy sical properties o f chalcog enide glasses are inf luenced by the presence of inher entdefects. T he addition of Bi ato ms into chalcog enide1IntroductionChalco genideg lassesar

9、 everyprom isingReceived data: 2009 11 09; Modified data: 2010 03 08Foundation i tem: This w ork was financially sup ported by the National Natural Science Foundation of Chin a ( 50972040) and the Fund of M ornin g Program of Wu han S cien ce an d T echnology Bu reau ( 200950431161)Biography: PAN Ru

10、i kun ( 1974- ) , male. Res earch Field: Photoel ect ron an d Inf ormation M aterials. E mail: panru ikun5 yahoo. com. cn .Correspondi ng author: ZH ANG T ian jin ( 1965- ) , male. Res earch Field: Ferr oelectric M aterials and intergrated devices. E mail: t j65zhang yahoo. com. cn.潘瑞琨, 等. 脈沖激光沉積法制備

11、Ge Se Bi 硫系玻璃薄膜的結(jié)構(gòu) 689 第 28 卷第 5 期glasses pro duces a remarkable change i. e. , fr om p to n ty pe conduction 1 . M any r eports fo cused onGe20 Bix Se80- x bulk glasses and therm al evaporatedonto the chemically cleaned microscope glass slides. The targets w er e ablated in a vacuum cham ber at a b

12、ackg round pressure of 2 10- 4 Pa w ith the laser energy 200m J/ pulse. The incident laser beam w as fo cused to the average f lux of about 5 J/ cm2 . The distance fr om the targ et to the substrate is about 8cmin an o ff / ax is appro ach geom et ry .film s 2 4 .GeSe2isatypicalchalcogenidesemico nd

13、uctor, w hich can be easily prepared either in glass form or in crystalline fo rm. In r ecent years, much research of GeSe2 g lasses has been m ade fo rstudying rigidity percolation, short and interm ediate 5 7rang e order of the st ructure.PLD technique has several adv antages for thin film prepara

14、tio n, such as the stoichiometric transferfro m the original targ et m aterial to a g iven substrate, 11, 12( GeSe2 ) 100- xBix f ilm s w er e deposited at roomtemperature. T he pulse repetition rate w as set at 4H z and the incidence angle w as 45#. Film samples w ere annealed near the glass t rans

15、ition temperatur es fo r 1h in the PLD vacuum chamber at pressure of 2 10- 4 Pa.The homogeneity of the sam ples w as confirm edby an electron pr obe X ray microanaly zer ( EPM A)t ime 8 10 .the easy set up and short pro cessIt isnecessary to investig ate the st ructure of Bi doped GeSe2 film s prepa

16、red by PL D. A s deposit ed f ilms prepar ed w ith high energ y density of the laser beamar e far f rom the equilibrium state. Annealing w ill( JEOL ,JCXA 733 ) .AnX rayfluorescencespectrophoto meter ( Shim adzu, XRF 1800) w as used fo r the deter mination of compositions of the film s.The t ransmis

17、sion spectra and absorption spectraof the studied f ilms w er e measur ed using acause changes in the st ructure andof the pulsed laser deposited films, interesting to be investigated.optical pro pertieswhich isIn this paper, ( GeSe2 ) 100- x Bix ( x = 0 12) f ilms w ere prepared by PLD. g w ere der

18、ived f rom the absorption spectra. The chang es in the o ptical band gaps o f the f ilms caused by Bi additio n and ther mal annealing w ere discussed. T he st ructural chang es in the studied film s w er e confirmed by Ram an spectraanalysis.spectrophoto meter ( Shimadzu,U V 1601 ) .T heEoptRaman s

19、pectra of the f ilms w ere measur ed at roomtemperaturebyusingaRam anspectrometer( Renishaw ,inVia )inbackscattering( 180#)config ur at ion. Laser irradiation at the w avelength of514 nm w as used for the ex citatio n. T he laser pow erw as pro perly set under an appr oxim ate2. 0m W to av oid damag

20、e on the samples.- 1resolution of the Raman spectra w as 1cm.level ofThe2Experimental3Results and discussionThe targets used for PLD were bulk glasses with stoichiom et ry ( GeSe2 ) 100 - x Bix ( x = 0, 0. 4, 2, 4, 8,12) . Glasses w ere sy nthesized f rom high purity elements ( Ge, Bi and Se, all o

21、f 5N pur it y ) in ev acuated ( 10- 2 Pa) and flam e sealed silica am poulein a ro cking furnace. The mix ture w as melted atabout 950 ! for 12h. A ft er that, the ampoule wasThe EPM A and XRF measurements showthatarethechemicalcompositionsofthefilmsho mog enous and close to those of the used targ e

22、ts.The atom ic ratio o f the target is maintained w ithin 2% in the f ilm deposited by PLD. The XRD patter ns confirquenchedin corresponding2h. The bulkcoldwaterthenannealednearmed theam orpho uscharacteroftheassited and annealed films.depoglass t ransition temper ature ( Tg ) fo rsample w as obtain

23、ed by taking it outFig. 1 sho w s the optical t ransmissio n spectra offro m the ampoule. T he glass r od w as f inally cut into 2mm thick targets for the depo sit ion.Thin films were prepared from the targ ets by thePLD technique using a KrF ex cimer laser o perated at the w aveleng th o f 248nm. T

24、 he films w ere depositedtheas depo sitedf ilms.Thepositionsoftheabsorption edges o f films shift to lo ng er w av elength w it h increasing Bi content. Fig . 2 show s the optical absorption spectra of the as deposit ed film s. In thest rong absorptio n r eg ion ( the absor ption co ef f icient 690

25、材料科學(xué)與工程學(xué)報(bào)2010 年 10 月 104 cm- 1 ) , the absor ption co ef f icient is given by the follow ing quadratic equation according to themodel pr opo sed by T auc 13 ,%non direct t ransition&op t 2( hv - Eg )( hv ) = B( 1)hvWhere B is a constant, is the pho to n energy andEoptoptg is the T auc optical band g

26、ap. The values of E g0 intersects of ( h ) 1/ 2 vs.can be derived f rom the =hplo ts ( see Fig . 3) . Fig. 3 indicates that non direct transition is the mechanism responsible for the opticalabso rption in this spectr al reg ion of the assited and annealed ( GeSe2 ) 100- x Bix f ilms.depoFig. 1 Optic

27、al t ransmittance s pect ra of asdeposited ( GeSe2 ) 100- x Bix f ilmsFig. 4 show s the Ram an spectra of the asdepo sited and annealed ( GeSe2) 100- x Bixfilms,respectively.For the as deposited f ilms,a bro ad plateau for the w av e number low er than 150cm- 1 isrelated to unresolv ed lat t ice mod

28、es. T he w eak- 1shoulder near 175cmcan be attributed either to thest retching mo de o f the Se3 Ge GeSe3 ethane chains ( x= 0) or to the A 1g mode in Bi2 Se3 pyramidal units ( x 0 ) .T he lat ter is mainly due to the Bi Se 14bo nd 15, 16 .The main band near 197cm- 1 is assig nedFig. 2 Opti cal abso

29、rption spectra of asdeposited ( GeSe2 ) 100- x Bix f ilmsFig. 3 Determination of the optical gaps in terms of T au cs law as lin ear extrapolation of the st rongabsorption data. ( a) As deposited f ilms; ( b) Annealed film s.to the A 1v ibration modes of the co rner sharingspectra o f studied sam pl

30、es is a bro ad o ne 330cm- 1 ) , o f mo derate intensity , w hich( 235 contains 16GeSe4/ 2 tetrahedrons. 213cmcan probably breathingvibrations oftetrahedrons 16, 17 . DueThe com panio n peaknearAc1 bi- 1several vibration bands.The m ain bands can be assig ned to the A 1 stretching m ode of Sen chain

31、s and Se8 ring molecules ( near 240 and 254cm - 1 ) 5 , theSe Se bonds in rings and Se Se st retching modesbe assignededge shar edto theGe2 Se8/ 2to higher disorder,laserablated film s co ntain higher density o f Se Se bonds ( formation of w rong bonds ) and larg e amo unts of molecular frag ments (

32、 including Sen chains) compar edw it h bulk glasses. T he second band o f the Ramancm- 1 ) 5, 14 ,( near260 and 280F2 antisymm et ricvibr at ion mo des of GeSe4/ 2 based st ructur al units( near 310 cm- 1 ) 17 .潘瑞琨, 等. 脈沖激光沉積法制備Ge Se Bi 硫系玻璃薄膜的結(jié)構(gòu) 691 第 28 卷第 5 期Fig. 4 Ram an spectra of ( GeSe2 ) 100

33、- x Bix f ilms. ( a) As deposited; ( b) An nealed.Bi addition caused three changes in the asaver age bo nd energ y has been proposed to contribute to such decrease of the optical band g aps in Ge Bi Se film s 2 . T he bond energ y o f Bi Se is sm aller than that of Se Se. As show n in Fig. 4, Bi add

34、ition causes the increase of the density of Bi Se bond and the decreasing of the density of Se Se bo nd w hile the Ge Se bo nd almo st doesnt changes. So the av er ag e bo ndenergy in the as depo sited f ilms decreased w ithdepo sited film s,w hichare consistent w ith thereports 2, 3, 16 .T he sho u

35、lder near 175cm- 1 becamest ronger and str ong er w hile the broad band ( 235330cm- 1 )is reduced, and the com panio n peak near213cm- 1 became w eaker w ith increasing Bi content.Annealing leads to tw o majorchang es in thethe broad band after annealingfilms as sho wn in Fig. 4( b) .Firstly,- 1incr

36、easing Bi content.Fig . 5 alsoshow s thatfro m 235 to 330cmis enhancedoptannealing increases E g o f the film s ex cept in x = 2film. Fig. 4 of Ram an spectra confirm s that averagebo nd energy in the as deposited f ilms increases afterex cept fo r the GeSe2 film ( x = 0) , w hich means thatthe dens

37、ity of Se Se bo nds increased. Secondly, the- 1shoulder near 175cmbecome weaker ex cept fo r theGeSe2 f ilm ( x = 0) , w hich means more Se Se bondsannealing.On the other hand,M . M .Hafizoptat t ributed the decrease of E g to the number of Bi Se bo nds 19 . Bi addition increased the number of Bi Se

38、 bo nds, w hich fo rmed tails of states extending theband into the m obility gap.at the ex pense of Bi Bi bonds. For the GeSe film ( x2= 0) , annealing decreases the Se Se hom opo lar bond. M o re Se3 Ge GeSe3 units and edge shared Ge2 Se8/ 2 bi tetrahedra for med at the ex pense of Se Se bonds duri

39、ng thermal annealing. M. Kincl et al. ex plained thermal induced decrease of hom opolar bonds by chang es o f st ructure and bondingarr angement.Fig. 5 show s that Bi addition decreases Egoipnt theas deposited f ilms m onotonously.T he decreasingB1/ 2Fig . 6 show s that the Tauc slopesaredif ferent.

40、 T he B1/ 2 values of the as depo sited f ilm are smaller than those of annealed f ilm s. And the higher the Bi content, the smaller the T auc slopes B . The parameter B in Eq. ( 1) is assumed to be an indicato r of the degree of structural randomness of amorpho us semico nductors. T he smaller the

41、B value, the higher the st ructur al diso rder 13 . Introducing Bi ato ms can increase the disorder of Ge Se netw ork in the materials . H igh concentration of localized states isresponsible f or the relatively low g in the asdepo sited f ilms. So Bi addition increases the disorder 181/ 2 20E optopt

42、of the f ilms and then decreasesg .It can beEdeduced that the films deposited at ro om temperature have hig her disor der than the annealed f ilms. H eattr eatment pr ocess can anneal out so me unsaturated defects 19 .Fig. 5 Dependen ce of the optical band gap on Bi conten t( mol % ) f or ( GeSe2 )

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