沉积参数对射频磁控溅射制备的碲锌镉薄膜的影响(英文)
2024-10-18
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第32卷第2期 红外与毫米波学报 Vo1.32,No.2 2013年4月 J.Infrareal Millim.Waves April,2013 文章编号:1001—9014(2013)02—0097—05 DOI:10.3724/SP.J.1010.2013.00097 Effects of deposition parameters on Cd1. Zn Te iflms prepared by RF magnetron sputtering CAO Hong ,CHU Jun.Hao ,WANG Shan Li ,WU Yun—Hua ,ZHANG Chuan.Jun ,。 (1.National Laboratory for infrared physics,Shanghai Institute of Technical Physics, Chinese Academy of Sciences,Shanghai 200083,China; 2.ShangHai Center for Photovoltaics,ShangHai 201201,China) Abstract:Cd1 Zn Te films were deposited by RF magnetron sputtering from Cdo 96 Zn0Te crystals target at different sub— .04strate temperatures,RF powers and working pressures.After deposition,the samples were annealed in high purity air at 473 K.The films were characterized using step profilometer,UV・VIS—NIR speetrophotometer,XRD and SEM.Depending on the deposition parameters and annealing,the values of the band gap of the CZT films varied between 1.45 and 2.02 eV. Key words:Cdl Zn Te;thin films;RF magnetron sputtering;band gap PACS:78.67.Pt,81.15.Cd.78.55.m ・ 沉积参数对射频磁控溅射制备的碲锌镉薄膜的影响 曹 鸿 , 褚君浩 , 王善力 , 邬云骅 , 张传军 (1.中国科学院上海技术物理研究所红外物理国家重点实验室,上海200083; 2.上海太阳能电池研究与发展中心,上海201201) 摘要:采用cd。 zn。 Te靶,利用射频磁控溅射制备碲锌镉薄膜,通过改变基片温度、溅射功率和工作气压,制得 不同的碲锌镉薄膜.将制备的碲锌镉薄膜放置在高纯空气气氛中,在473 K温度下退火.利用台阶仪、分光光度计、 XRD和SEM测试设备表征,结果表明,通过退火和改变沉积参数,可以制备出禁带宽度在1.45—2.02 eV之间调 节的碲锌镉薄膜. 关键词:碲锌镉;薄膜;射频磁控溅射;带隙 中图分类号:0484.1 文献标识码:A Introduction alloy films grown by RF magnetron sputtering in thin— iflm solar cells have attracted more and more attention The Cd1一 Zn Te(CZT)is known as a direct from some researchers.RF magnetron sputtering is one wide—band gap semiconductor.Its band gap can be tai- of the best options for commercialization,having the lored between 1.45 eV(CdTe)and 2.26 eV(ZnTe) advantages of simple and low cost instrumentation, by adjusting the film composition.CZT is one of the good reproducibility,high efifciency of material utiliza— important semiconductor materials used in the top cell tion and hi gh growth rate. of tandem solar cells,electro—optical modulators,pho— In order to get CZT films with desirable proper— toconductors,light emitting diodes,X—ray and gamma ties,different RF magnetron sputtering technologies ray deteetors.ete.[ 4。. have been applied.CZT films were prepared using in— In recent years,research and applications of CZT terdiffusion of sputtered layers of CdTe and ZnTe E . Received date:2012-08-13,revised date:2012—12・10 收稿日期:2012-08・13,修回日期:2012-12-10 Foundation items:Supposed by the Knowledge Innovation Program of Chinese Academy of Sciences(KGCX2 YW-347) Biography:CAO Hong(1977・),female,Ph.D.Research field focus on photovohaic structure and characteristics.E-mail:hongeao0606@yahoo.COB.cn 98 红外与毫米波学报 32卷 CZT films were also tried by CO.sputtering from a ZnTe. Cd target_o .Muhilayered CdTe/Zn structures were deposited by a muhilayer method .In this work. CZT films were grown by RF magnetron sputtering on glass substrates,using Cdo 96 Zno 04 Te crystal target with 50 mm diameter.The characteristics of the as. grown films have been investigated by step profilome. ter,UV—VIS—NIR spectrophotometer.XRD and SEM. 1 Experimental CZT films were fabricated by RF magnetron spur. tering on glass substrates.The sputtering target was cut from Cdo 96Z“0 04Te ingot with diameter of 50 mm.The sputtering chamber was evacuated to 8 pressure less than 3.0 X 10。Pa.Argon(99.999%)was admitted under control(gas flow 28.7 sccm)through a needle valve.The RF powers used in the growth process were 20 W,36 W and 50 W at the working pressure 2.4 Pa.The working pressures used in the growth process were 2.0 Pa,2.4 Pa and 3.8 Pa at the RF power of 36 W.A deposition time of 30 min was used. CZT films were deposited at different substrate temper. atures:473 K,573 K and 673 K at working pressure 0f 2.4 Pa and RF power of36 W.A deposition time 0f 60rain was used in the growth process.A series of CZT iflms were prepared by changing the process parameters (see Table 1).CZT flms deposited at different sub。 strate temperatures were annealed in high purity air for 40 min at 473 K. Tablel The preparation conditions of CZT thin films 表I CZT薄膜的制备条件 2 Results and discussion Figures 1—。3 show the transmission spectra for CZT films grown at various deposition parameters.Fig— ure 4 shows the transmission spectra of heat—treated CZT samples deposited at various substrate tempera・ tures.The spectra have consistent features,including coherent district,absorption edge and full absorption area。The difference of all samples lies in absorption edge position.According to semiconductor theory,ab— sorption edge position corresponds to band gap. Fig.1 Transmission spectra of CZT films deposited under different working pressures 图1 不同工作气压条件下制备的CZT薄膜的透射谱 iFg.2 Transmission spectra of CZT films deposited with different RF powers 图2不同溅射功率条件下制备的CZT薄膜的透射谱 Fig.3 Transmission spectra of CZT films deposited at dif- terlent substrate temperatures 图3 不同基片温度条件下制备的CZT薄膜的透射谱 The transmission data are used to calculate ab sorption coefifcient of the CZT films at different wave— 2期 CAO Hong et al:Effects of deposition parameters on Cd1 Zn Te films prepared by RF magnetron sputtering Fig.4 Transmission spectra of heat—treated CZT films de— posited at different substrate temperatures 图4不同基片温度下制备的CZT薄膜退火后的透射谱 lengths.The absorption coefficient Ot is given by the re— lation[ : ,:Ioexp(一 d) , (1) where I is the intensit【Ⅲu\ Jy of transmitted li/ _【 【^《 ght,I is the in— tensity of incident light and d is the thickness of CZT iflms. As the transmittance is defined as I/lo,we obtain rfom Eq.(1).In the high absorption region(Ot≥10 cm ),the photon energy dependence of the absorp・ tion coefficient can be described by the quadratic rela— tion[9l: (ahv) =A(hv—E ) , (2) where is the frequency of the incident beam,A is a constant and Eg is the optical gap.So if we plot (ahv) VS砌then the intercept of the straight line on the砌axis gives US the value of band gap E .Plots of (ahv) VS hv for CZT films are shown in Figs.5~8. respectively.In order to determine the band gaps of all samples,plots in Figs.5~8 were fitted.Table 2 is the iftting results of CZT thin iflms. The direct band gapof the CZT film increases .with the increase of RF power and decreases with the increase of working pressure. Due to the difference of Ar plasma on the energy transfer efficiency of Cd,Zn and Te atoms,in the sputtering process,the quantitative relationship is[1o]: 4MlM2 , (3) where M1 is the quality of the incident ion(Ar ),M2 is the quality of the target atom.Energy transfer coeffi. cient of Ar on each atom can be computed according. hv/eV Fig.5(ahv)。VS hv plots ofCZT thin iflms depos— ited under different working pressures 图5不同工作气压条件下制备的CZT薄膜带隙 的拟合结果 _【g。/. ̄3J~邕_【 《3 ^g。/>0 0_hv/eV Fig.6(ahv) VS hv plots of CZTthin iflms deposi. ted with different RF powers 图6不同溅射功率条件下制备的CZT薄膜带隙 的拟合结果 hv/eV Fig.7(othv) VS hv plots of CZT thin iflms deposited at different substrate temperatures 图7不同基片温度条件下制备的CZT薄膜带隙的 拟合结果 ly: z =0.94,YAT=—cd=0.78, Ar一 0.73.So Zn atom shows sputtering advantage in the sputtered films. As RF power increases.the average energy of the sputtered particles is also enhanced.When the working 【.z 2期 CAO Hong et al:Effects of deposition parameters on Cd1一Zn Te films prepared by RF magnetron sputtering 101 posited films are polycrystalline with preferential sputtering on glass deposition from the Cdo 96 Zn0 o4 Te crystals target at different process parameters.The de— posited films are polycrystalline with preferential (1 1 1)orientation,it indicates that the growth of CZT ilfm at low temperature is kinetically limited.In the case of kinetically limited growth,it may be expected that grains with a faster growing orientation may grow at the expense of others[。 .(1 1 1)orientation.The band gap of the deposited iflms increases as RF power increases.The band gap of the This will result in a gradual deposited ilfms decreases with increasing working pres— sure or deposition temperature.Heat treatment has an increase in grain size.An additional factor is that re— crystallisation and grain growth may take place dynami— cally during growth,especially at high growth tempera- ture. important influence on CZT films deposited at substrate temperature below the annealing temperature.By ad— justing the heat treatment and preparation conditions, the band gap of respective CZT films can be tuned rom f1.45 t0 2.02 eV. 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