發(fā)布時(shí)間：2018-03-01 17:17

  本文關(guān)鍵詞： ZnO 摻雜 AgNW 遷移率 載流子散射　出處：《湖北大學(xué)》2016年博士論文　論文類型：學(xué)位論文

【摘要】：透明導(dǎo)電薄膜是把光學(xué)透明性能與導(dǎo)電性能復(fù)合在一體的光電材料,其在平板顯示器、太陽能電池、發(fā)光二極管、氣體傳感器、電磁屏蔽視窗、節(jié)能玻璃等光電器件領(lǐng)域獲得了廣泛的應(yīng)用和日益增大的市場需求。目前應(yīng)用最廣泛的透明導(dǎo)電薄膜是In_2O_3:Sn(ITO)薄膜,但是ITO材料的主要成分In是一種及其昂貴且稀有的元素,限制了 ITO薄膜的實(shí)際應(yīng)用潛力。我們要研究的氧化鋅(ZnO)是一種寬禁帶Ⅱ-Ⅵ族半導(dǎo)體材料,自然狀態(tài)下成六方纖鋅礦晶體結(jié)構(gòu)。摻雜的ZnO薄膜具有與ITO薄膜相當(dāng)?shù)母咄高^率和低電阻率的特點(diǎn),并且原料豐富、價(jià)格低廉、無毒、在氫等離子體氣氛中穩(wěn)定不易被還原,有望成為替代ITO的理想材料。本文首先采用射頻磁控濺射法在玻璃襯底上面制備出高質(zhì)量的A1摻雜ZnO(AZO)透明導(dǎo)電薄膜,用XRD、SEM、XPS和分光光度計(jì)等測試手段對沉積AZO薄膜的物相、形貌、成分、光學(xué)性能等進(jìn)行了表征和分析。用Van der Pauw方法對樣品的電學(xué)特性進(jìn)行了測量,并分析了 AZO薄膜的導(dǎo)電機(jī)制。在制備過程中通過改變襯底溫度、氧氬比、功率、氣壓等工藝條件,研究各個(gè)參數(shù)對于薄膜光電性能的影響,得出最佳的工藝參數(shù)。最終確定用射頻磁控濺射法制備AZO薄膜的最佳工藝條件為:摻雜濃度為2 wt%下,氧氬比0:30,襯底溫度為常溫,工作氣壓3Pa,功率120W。在此條件下制備的AZO薄膜其透射率達(dá)到80%以上,電阻率可達(dá)到1 × 10~(-3) Ω·cm數(shù)量級。在優(yōu)化工藝參數(shù)的基礎(chǔ)上,我們研究了 ZnO薄膜表面界面特性與光電性能的關(guān)聯(lián),以實(shí)現(xiàn)薄膜結(jié)構(gòu)的優(yōu)化設(shè)計(jì)。通過對AZO薄膜進(jìn)行退火處理、改變厚度的處理方法從表面與界面的角度來分析AZO薄膜微結(jié)構(gòu)與光電性能的演變規(guī)律,并通過高溫高濕的環(huán)境穩(wěn)定性實(shí)驗(yàn)來探索薄膜電學(xué)性能退化的機(jī)理。最終嘗試薄膜表面與銀納米線(AgNW)復(fù)合的方法,實(shí)現(xiàn)降低表面電阻和提高環(huán)境穩(wěn)定性的目的。首先退火結(jié)果的比較表明在真空中退火的AZO薄膜比未退火和空氣中退火的薄膜顯示出更低的電阻率,特別是真空退火后載流子遷移率明顯增大,結(jié)合Ols電子態(tài)分析判斷,其增大的遷移率主要源自于真空退火環(huán)境中AZO晶界處吸附的O向外界擴(kuò)散,晶界缺陷濃度降低,對載流子的散射作用減弱。此外,AZO薄膜越厚,結(jié)晶程度和擇優(yōu)取向都更好,遠(yuǎn)離界面處的晶粒逐漸合并長大,形成超大的晶粒,結(jié)構(gòu)也更加致密。當(dāng)AZO薄膜厚度達(dá)到2.5μm時(shí),載流子濃度和遷移率都明顯增大,電阻率可以達(dá)到8.24×10~(-4)Ω·cm。但是AZO薄膜厚度太厚時(shí),光學(xué)透過率會(huì)有所下降。然后我們研究了 AZO薄膜的環(huán)境穩(wěn)定特性,在室內(nèi)環(huán)境放置24天后AZO薄膜的方阻增大了 11.1%,而高溫高濕環(huán)境中薄膜的方阻增大了 95.5%。電學(xué)性能測試結(jié)果表明薄膜電學(xué)性能退化主要原因不是載流子濃度的下降,而是載流子遷移率的降低,結(jié)合XPS深度元素分析結(jié)果還可以發(fā)現(xiàn)O向內(nèi)部擴(kuò)散明顯,而且含有O_2、H_2O、CO_2等共價(jià)鍵較強(qiáng)的產(chǎn)物。最后我們嘗試在AZO薄膜上旋涂一層AgNW并進(jìn)行真空退火處理,復(fù)合薄膜的表面電阻可以從24 Ω/□降低到9.8 Ω/□,環(huán)境穩(wěn)定性也得到大幅改善。結(jié)合AZO薄膜的表面特性我們認(rèn)為,由于AgNW在AZO薄膜表面形成網(wǎng)狀結(jié)構(gòu)的導(dǎo)電通道,弱化了薄膜表面的晶界對載流子的散射效果,從而克服了濕熱環(huán)境通過AZO薄膜晶界帶來的負(fù)面影響。通過改變摻雜濃度及摻雜元素可以探究導(dǎo)電的機(jī)理及主要影響因素。隨著A1的摻雜濃度的增加,ZnO薄膜的導(dǎo)電性也發(fā)生變化,當(dāng)Al摻雜質(zhì)量分?jǐn)?shù)為2%時(shí),薄膜的導(dǎo)電性能最佳,其低的電阻率和高的載流子濃度主要原因是具有相對較高的有效摻雜率。通過在Ar和H_2混合氣氛濺射實(shí)現(xiàn)H鈍化Al摻雜ZnO薄膜可以有效的提高載流子濃度,薄膜的電子濃度達(dá)到6.416×10~(20) cm~(-3),電阻率也因此進(jìn)一步降低到6.49×10~(-4) Ω·cm,此時(shí)薄膜的光學(xué)帶隙也達(dá)到了 3.78 eV。H鈍化Al摻雜的結(jié)果表明H不僅可以影響AZO薄膜的結(jié)構(gòu),鈍化薄膜晶界缺陷,還會(huì)扮演電子施主的角色提高薄膜的導(dǎo)電性,故H的摻雜有利于獲得高性能AZO透明導(dǎo)電薄膜。相對于ZnO薄膜而言,In、Ga共摻的ZnO薄膜可以明顯改善和提高載流子遷移率,其值達(dá)到24.01 cm~2/Vs,但是載流子濃度并不高,只有2.74×10~(20)cm~(-3)。XPS測試其元素深度分布可以推測摻雜的ZnO薄膜內(nèi)部的施主主要來源于替位摻雜缺陷,而不是O空位或間隙Zn缺陷。本文最后論了薄膜中幾種主要的載流子散射機(jī)制:雜質(zhì)離子散射、晶界散射和極化光學(xué)聲子散射機(jī)理,確定了每種機(jī)理的推理和計(jì)算公式。通過ZnO、AZO和IGZO薄膜的變溫電學(xué)性能測試,特別是不同薄膜的載流子遷移率隨溫度的變化,探究每種散射機(jī)理對薄膜遷移率影響的強(qiáng)弱。首先發(fā)現(xiàn)極化光學(xué)聲子散射限制的遷移率隨著溫度升高而迅速下降,但是溫度升到室溫時(shí),遷移率仍然遠(yuǎn)大于200 cm~2V~(-1)s~(-1),對遷移率的限制不占主導(dǎo)作用。對于ZnO薄膜來說,晶界散射起主要的限制作用,而對于IGZO薄膜來說,由于隧穿電導(dǎo)的作用,雜質(zhì)離子散射是主要的限制機(jī)理。而熱電子發(fā)射遷移率與電子隧穿遷移率均與載流子濃度和晶界缺陷態(tài)密度密切相關(guān),通過圖解可以發(fā)現(xiàn),溫度、晶粒尺寸、載流子濃度和晶界缺陷態(tài)密度四個(gè)因素共同影響雜質(zhì)離子散射、晶界散射和極化光學(xué)聲子散射這三種電子傳輸機(jī)制之間的競爭與平衡關(guān)系。
[Abstract]:The transparent conductive film is the photoelectric material and the conductive performance of the optical properties of the composite in the transparent one, the flat panel display, solar cells, light-emitting diodes, gas sensors, electromagnetic shielding windows, glass and other optoelectronic devices is widely used and the increasing market demand. Currently the most widely used transparent conductive film is In_2O_3:Sn (ITO) film, but the main ingredients of ITO materials and In is an expensive and rare element, limiting the application potential of ITO films. We need to study the Zinc Oxide (ZnO) is a kind of wide band gap II-VI semiconductor material, the six party wurtzite structure into ZnO under natural condition. The film doped with ITO thin film is high transmittance and low resistivity characteristics and abundant raw materials, low price, non-toxic, the hydrogen in the plasma atmosphere is stable and is not easy to be restored, is expected to become The ideal material to replace ITO. Firstly, using RF magnetron sputtering method on glass substrate were prepared by doping A1 high quality ZnO (AZO) transparent conductive thin film, XRD, SEM, XPS and photometer for deposition of AZO thin film phase, morphology, composition and optical properties of the characterization and analysis. The electrical characteristics of samples using Van der Pauw method were measured and analyzed the conduction mechanism of AZO thin films. By changing the substrate temperature in the preparation process, oxygen argon ratio, power, pressure and other process conditions, effects of various parameters on the electrical properties of thin films, the optimum parameters the final to determine the optimum conditions for preparation of AZO films by RF magnetron sputtering as the doping concentration is 2 wt%, ratio of oxygen and argon at 0:30, the substrate temperature is room temperature, working pressure 3Pa, 120W. power under the condition of AZO thin films prepared by the transmittance reached 80% Above, the resistivity can reach 1 * 10~ (-3). The level of CM. Based on the optimization of process parameters, we studied the association of surface and interface properties of ZnO thin film and photoelectric properties, in order to achieve the optimal design of thin film structure. Based on the AZO thin films were annealed, the thickness change processing method from surface and interface the perspective of the evolution and photoelectric properties of AZO thin film micro structure, and through the stability test of high temperature and high humidity environment to explore the mechanism of the degradation of electrical properties of the films. The final attempt to film and silver nanowires (AgNW) composite method, can reduce the surface resistance and improve the stability of the environment. The first annealing that the AZO films annealed in vacuum than annealed without annealing in air and show lower resistivity, especially after annealing in vacuum carrier mobility increased significantly with Ols State analysis, the increasing mobility mainly from the vacuum annealing environment in AZO grain boundaries. The adsorption of O to the outside diffusion, grain boundary defect concentration decreased, reduced scattering effect on the carrier. In addition, the AZO film is thicker, degree of crystallinity and orientation are better, far away from the interface with grain gradually grew up, the formation of large the grain, the structure is more compact. When the thickness of AZO film reached 2.5 m, carrier concentration and mobility are obviously increased, the resistivity can reach 8.24 * 10~ (-4) cm. AZO. But the film thickness is too thick, the optical transmittance will decline. Then we study the environmental stability characteristics of AZO thin films in the indoor environment, after 24 days of AZO thin film resistance increased by 11.1%, while the resistance film of high temperature and high humidity environment. The test results show that the electrical properties of 95.5%. thin film electrical property degradation is not the main reason for the carrier The decrease of the concentration, but lower carrier mobility, combined with the results of XPS depth elements can also be found in O to the internal diffusion is obvious, but also contains O_2, H_2O, CO_2 and other strong covalent products. Finally we try on the AZO film coated with a layer of AgNW and vacuum annealing treatment, surface resistance of composite films can from 24 to 9.8 ohms / lower - Omega / -, environmental stability has been greatly improved. Combined with the surface properties of AZO films we think, because the AgNW forming conductive channel network structure on the surface of AZO film, the weakening of the scattering effect on the carrier of grain boundary film surface, so as to overcome the negative effects of hygrothermal environment through the AZO grain boundary film bring. By changing the doping concentration and doping elements can be conductive to investigate the mechanism and the main influence factors. With the increase of A1 doping concentration, the conductivity of ZnO films is also changing, when Al The doping concentration is 2%, the best performance of the conductive film, low resistivity and high carrier concentration is the main reason for having relatively high effective doping ratio. Through the realization of H passivation of Al doped ZnO films on Ar and H_2 mixed atmosphere sputtering can effectively improve the carrier concentration, the electron concentration reached to 6.416 * 10~ (thin film 20) cm~ (-3), so the resistivity is further reduced to 6.49 * 10~ (-4). Cm, the optical band gap of the films reached 3.78 eV.H passivation doped Al results show that H not only can influence the structure of AZO thin film, passivation film boundary defects, the conductivity will play the role of improving film electron donor therefore, H doping is beneficial to obtain high performance AZO transparent conductive films. Compared with the ZnO film, In, ZnO Co doped Ga thin films can be obviously improved and enhanced carrier mobility, its value reached 24.01 cm~ 2/Vs, but the current carrying Concentration is not high, only 2.74 * 10~ (20) cm~ (-3).XPS test ZnO film internal donor the depth profile of elements can be doped mainly from substitutional doping defects, rather than the O vacancy or interstitial defects. Finally, Zn on several main carrier scattering mechanism in the film: impurity ions scattering and grain boundary scattering, polar optical phonon scattering mechanism, reasoning and calculation formula for each mechanism is determined. Through ZnO, the electrical properties of temperature test of AZO and IGZO films, especially films of different carrier mobility versus temperature on each scattering mechanism of the film mobility influence. The first migration polar optical phonon scattering limit rate decreased rapidly with the increasing of temperature, but the temperature to room temperature, the migration rate is still far greater than 200 cm~2V~ (-1) s~ (-1), the mobility restriction does not play a dominant role for the ZnO. Film, play the main role in the grain boundary scattering limit, and for IGZO thin films, due to the tunneling conductance effect, scattering of impurity ions is limited. The main mechanism of the thermal electron emission and electron tunneling mobility mobility and carrier concentration and grain boundary defect density is closely related, through diagrams can be found in temperature grain size, carrier concentration, grain boundary and defect density of four common factors that affect the scattering of impurity ions, the relationship between competition and balance between grain boundary scattering and polarization optical phonon scattering of the three electron transfer mechanism.

【學(xué)位授予單位】：湖北大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TB383.2

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