本文選題：碲鋅鎘　切入點：深能級缺陷　出處：《西北工業(yè)大學(xué)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：化合物半導(dǎo)體碲鋅鎘(CdZnTe)晶體被認為是最具潛力的室溫半導(dǎo)體核輻射探測器材料。然而由于生長過程以及后續(xù)器件制備過程的復(fù)雜性,在晶體內(nèi)部形成各種缺陷,對載流子輸運過程以及器件性能產(chǎn)生嚴重影響,制約著高品質(zhì)CdZnTe成像探測器的發(fā)展。本文重點研究CdZnTe晶體中缺陷對載流子輸運過程以及器件性能的影響,揭示晶體中點缺陷、擴展缺陷以及輻照損傷誘生缺陷對載流子輸運過程影響的微觀機制,提出優(yōu)化探測器性能,尤其是時間響應(yīng)特性以及抗大劑量照射的方法。研制了一套激光誘導(dǎo)瞬態(tài)光電流(LBIC)測試系統(tǒng),用于分析測試高電阻半導(dǎo)體的載流子遷移率等載流子輸運參數(shù)。構(gòu)建了CdZnTe晶體載流子輸運特性的基本物理模型,確立了不同條件下激光誘導(dǎo)瞬態(tài)光電流譜的解譜分析方法。采用該方法可直接得出表面復(fù)合速率、俘獲時間、去俘獲時間、載流子遷移率、空間電荷密度等系列載流子輸運特性參數(shù)。采用均勻電場下的解譜法對不同電壓下的LBIC圖譜進行分析得出,CdZnTe晶體典型電子遷移率約為950 cm2/V-s,對應(yīng)的電子遷移率壽命積為1.32×10-3cm2/V,載流子發(fā)射率與電場的平方根呈線性關(guān)系。由此得出,電場對缺陷能級的去俘獲效應(yīng)影響的主導(dǎo)機制為Poole-Frenkel效應(yīng),即電場可以有效增強載流子去俘獲效應(yīng),從而達到高的載流子收集效率。采用光致發(fā)光譜(PL)和熱激電流譜(TSC)對晶體內(nèi)部缺陷分布進行了精確測試與分析,結(jié)合無接觸式微波光電導(dǎo)(MWPCD)、LBIC技術(shù)以及能譜響應(yīng)特性研究了不同缺陷分布對載流子輸運過程和器件性能的影響。采用Hornbeck-Haynes模型對MWPCD分析結(jié)果表明,MWPCD曲線快降部分主要由體復(fù)合作用主導(dǎo),慢降部分主要由載流子去俘獲效應(yīng)主導(dǎo)。同時發(fā)現(xiàn),A中心以及位錯相關(guān)的缺陷能級可顯著的降低CdZnTe晶體的體復(fù)合壽命。Te反位和Te間隙可能是導(dǎo)致去俘獲時間增長以及電荷收集不完全的主要缺陷。缺陷能級的去俘獲時間小于收集時間的特性有利于提高探測器性能。為了保證成像器件應(yīng)用時具有足夠高的計數(shù)率,同時避免引入過高的漏電流,采用亞禁帶光照辦法進行了CdZnTe晶體缺陷能級占據(jù)概率及空間電荷分布的調(diào)控,從而實現(xiàn)優(yōu)化。研究結(jié)果表明,亞禁帶光照后CdZnTe晶體的電阻率由約1.23×10m Ω·cm下降到約4.22×109Ω·cm,同時I-t曲線的弛豫時間從8.21 s減小到0.93 s。結(jié)合改進的SRH模型分析發(fā)現(xiàn),亞禁帶光可有效調(diào)節(jié)缺陷能級的占據(jù)概率,使得活性陷阱能級的濃度減低。通過對比亞禁帶光照前后LBIC圖譜可知,亞禁帶光照后晶體內(nèi)部空間電荷濃度從9.03×109cm-3下降到8.67×108cm-3,從而有效的抑制了載流子俘獲效應(yīng),使內(nèi)建場畸變減小。由241Am@59.5keV能譜效應(yīng)特性測試可知,亞禁帶光照有效提高了低電壓下探測器的能量分辨率,使得探測器的收集效率提高。根據(jù)Hecht公式擬合可知,亞禁帶光照后電子遷移率壽命積從8.59×104 cm2/V提高到1.17×10-cm2/V。由于載流子在擴展缺陷周圍的輸運與點缺陷有很大不同,本文首先建立了擴展缺陷周圍的勢壘調(diào)控俘獲模型,并結(jié)合α源誘導(dǎo)電流技術(shù),分析擴展缺陷對電子輸運過程和能譜響應(yīng)特性的影響。研究結(jié)果表明,擴展缺陷俘獲電子后在其周圍會產(chǎn)生明顯的肖特基型耗盡區(qū),使得內(nèi)部電場畸變。結(jié)合LBIC測試得出包含晶界樣品的有效電子遷移率為803 cm2/Vs,明顯小于單晶樣品910 cm2/Vs的電子遷移率。通過α源誘導(dǎo)電流信號上升時間統(tǒng)計分布得出,晶界會對電子漂移時間產(chǎn)生固有的擾動影響,且無法通過提高電壓來抑制。結(jié)合α源誘導(dǎo)電流信號幅值統(tǒng)計分布發(fā)現(xiàn),晶界作為載流子的復(fù)合區(qū)域,在低能端形成第二個峰,最終造成電荷收集不完全,影響探測器響應(yīng)的均勻性。采用超快脈沖X射線研究了不同劑量、不同電壓下CdZnTe探測器的時間響應(yīng)特性。結(jié)果表明,CdZnTe探測器的響應(yīng)時間約為2.2 ns。通過雙能級模型對非平衡載流子弛豫過程進行分析得出,自由載流子濃度隨時間變化率不只與缺陷能級的俘獲(復(fù)合)截面有關(guān),還與缺陷能級的占據(jù)概率有關(guān)。對不同入射劑量下CdZnTe探測器的時間響應(yīng)特性分析可知,CdZnTe晶體的極化閾值劑量約為2.78×109 photons mm-2s-1。由于能級占據(jù)概率的不同,大入射劑量時非平衡載流子主要通過復(fù)合作用快速弛豫到平衡態(tài)。而小劑量入射時,由于去俘獲效應(yīng)的影響,其時間響應(yīng)弛豫過程明顯延長。提高電壓可有效的避免載流子被俘獲以及增強載流子去俘獲效應(yīng),有利于提高探測器時間響應(yīng)特性。采用高劑量60Coγ射線為輻照源,研究了CdZnTe晶體中的能量沉積機理以及最終形成的穩(wěn)定缺陷形式,分析了輻照損傷對載流子輸運特性以及器件性能的影響。根據(jù)Kinchin-Pease理論,經(jīng)過一次康普頓散射后,Cd、Zn和Te原子獲得的最大能量分別為45.42 eV、78.11 eV和40.01 eV。根據(jù)Mott-McKinley-Feshbach經(jīng)典方程,CdZnTe晶體中康普頓反沖電子與不同晶格原子作用,其移位的截面比為σ(Cd):σ(Zn):σ(Te) =1:3.9:1.12。結(jié)合不同劑量照射下的PL結(jié)果可知,隨著輻照劑量的增大,A中心峰、A0X峰的強度不斷增強,DAP峰強度不斷減弱。該結(jié)果表明60Coγ射線在晶體內(nèi)部產(chǎn)生大量的VCd。VCd與InCd+結(jié)合形成穩(wěn)定的A中心。由LBIC測試結(jié)果可知,輻照損傷產(chǎn)生的缺陷主要通過增強電離雜質(zhì)散射的作用降低電子的遷移率。結(jié)合不同劑量下電子遷移率的變化關(guān)系,歸結(jié)出60Coγ射線對CdZnTe晶體電子遷移率損傷經(jīng)驗?zāi)Ｐ蜑?/μ=1/μ0+5.489×104-0.02676。輻照損傷引入的缺陷能級通過減低遷移率以及壽命,使電子的遷移率壽命積從1.36×10-3 cm2/V下降到7.56×10-4 cm2/V。同時,輻照損傷造成探測器的能量分辨率以及電荷收集效率的顯著降低。
[Abstract]:Compound semiconductor cadmium zinc telluride (CdZnTe) crystal was considered to be the most promising materials for room temperature nuclear radiation detectors. However, due to the growth process and the complexity of subsequent device fabrication process, the formation of various defects in the crystal, the carrier transport affect the transport process and device performance, restricts the development of high-quality CdZnTe imaging detector. This paper focuses on the defects in CdZnTe crystal transport process and device performance of carrier, reveal the point defects, extended defects and micro mechanism of irradiation damage induced defects in the transport process influence on carrier, optimize the detector performance, especially the time response characteristics and method of high dose irradiation. The development of a laser induced the transient photocurrent (LBIC) test system for analysis and testing of high resistance semiconductor carrier mobility and carrier transport The basic physical parameters. The construction model of CdZnTe crystal carrier transport properties, established the solution method of spectral analysis under different conditions of laser induced transient photocurrent spectrum. Using this method can obtain the surface recombination velocity, capture time, to capture time, carrier mobility, space charge density series carrier transport characteristic parameters. LBIC spectra of different voltages were analyzed using uniform electric field method, CdZnTe crystal typical electron mobility is about 950 cm2/V-s, corresponding to the electron mobility Lifetime product is 1.32 * 10-3cm2/V, the carrier rate and the square root of field emission showed a linear relationship. Thus, the electric field of the defect level to capture the effect of the dominant mechanism for the Poole-Frenkel effect, the electric field can effectively enhance the carrier to capture effect, so as to achieve high carrier collection efficiency. The photoluminescence spectrum (PL) and TSC spectrum (TSC) of internal defect distribution of crystal was accurate measurement and analysis, combined with contactless microwave photoconductivity (MWPCD), LBIC technology and the energy spectrum of different defect distribution transport process and device performance of carrier response. Using Hornbeck-Haynes model for MWPCD analysis the results show that the MWPCD curve is down by some of the main body of the composite leading role, slow down the main part of the carrier to capture the dominant effect. At the same time, the A center and dislocation related defects can significantly reduce the level of CdZnTe crystal body composite life trans.Te and Te clearance may be the main defects lead to capture time and growth the charge collection is not complete. The defect level to capture time less than collection time characteristics is helpful to improve the performance of the detector. In order to ensure the application of imaging devices with high enough count rate, the same Avoid introducing leakage current is too high, the sub bandgap illumination method of CdZnTe crystal defect level occupation probability and spatial regulation of the charge distribution, so as to realize the optimization. The results show that sub bandgap light after the resistivity of CdZnTe crystal is about 1.23 * 10m. Cm down to about 4.22 x 109. Cm. At the same time, the I-t curve of relaxation time is reduced from 8.21 s to 0.93 S. with the improved SRH model analysis showed that the sub bandgap light occupying probability can effectively adjust the defect level, the concentration of active traps reduced. By comparing the sub bandgap light and LBIC spectra, sub bandgap light inside the crystal from space charge concentration 9.03 x 109cm-3 decreased to 8.67 * 108cm-3, which effectively inhibits the carrier trapping effect, the built-in field distortion. By 241Am@59.5keV spectrum effect characteristic test shows that sub bandgap illumination can effectively improve the low voltage Under the energy resolution of the detector, the collection efficiency of the detector is improved. According to the Hecht formula fitting, sub bandgap light electron mobility Lifetime product increased from 104 cm2/V to 8.59 * 1.17 * 10-cm2/V. as carrier in the transport and transport extended defects around the point defect is quite different, this paper extended barrier regulation capture the model around the defects, combined with alpha source induced current technology, analysis of extended defects on the response characteristics and the energy spectrum of the electron transport process. The results show that the extended defects capture electrons around it will produce obvious Schottky type depletion region, the internal electric field distortion. Combined with the LBIC test including grain boundary samples effectively the electron transfer rate of cm2/Vs was 803, significantly less than single crystal samples 910 cm2/Vs electron mobility. The induced current signal rise time distribution obtained by alpha source, grain boundary The disturbing effects inherent to electron drift time, and not to suppress by increasing the voltage. Combined with alpha source induced current amplitude distribution, grain boundary as composite carrier area, formed second peaks in the low end, resulting in incomplete charge collection uniformity, influence of detector response were studied by different doses. Ultrafast X ray pulse response time of CdZnTe detector under different voltage. The results show that the response time of CdZnTe detector is about 2.2 ns. on the nonequilibrium carrier relaxation process analysis by two-level model, the capture rate not only with the defect level changes in the free carrier concentration with time (composite) section, but also on the with probability occupy the defect level. Characteristics analysis of response to different dose of CdZnTe time of the detector, the polarization threshold dose of CdZnTe crystal is about 2.7 8 x 109 photons mm-2s-1. due to different level occupation probability, large incident dose of non equilibrium carriers mainly through the compound effect of fast relaxation to the equilibrium state. The small dose of incidence, due to trapping effect, the response time was significantly prolonged. The relaxation process can effectively improve the voltage to avoid capture and enhanced carrier carrier to capture the effect, can improve the response time of the detector. The high dose of 60Co gamma ray as radiation source, studied the mechanism of energy deposition in CdZnTe crystals and finally formed the stable defect form, analysis of radiation damage in transport properties and device performance of carrier. According to Kinchin-Pease theory, after a Compton scattering Cd, Zn and Te atoms, the maximum energy obtained is 45.42 eV, 78.11 eV and 40.01 eV. according to the Mott-McKinley-Feshbach equation, CdZnTe crystal Compton recoil electron with different lattice atoms, the displacement area ratio (Cd): sigma sigma sigma (Zn): (Te) =1:3.9:1.12. with different doses of irradiation PL results showed that with the increase of irradiation dose, A peak, A0X peak intensity increasing, DAP peak intensity decrease. The results show that the 60Co gamma ray VCd.VCd and InCd+ in a lot of crystals combine to form a stable A center by LBIC. Test results show that the main defects of radiation damage by enhancing the ionized impurity scattering effect reduce the electron mobility. Combined with the relationship between different doses of electron mobility, summed up the 60Co gamma ray migration the damage rate of empirical model is 1/ mu =1/ mu 0+5.489 * 104-0.02676. irradiation defect level introduced by reducing the mobility and lifetime of CdZnTe crystal electron, make the electron mobility Lifetime product from 1.36 * 10-3 cm2/V down to 7.5 At the same time, the energy resolution of the detector and the charge collection efficiency are significantly reduced by radiation damage at the same time of 6 x 10-4 cm2/V..

【學(xué)位授予單位】：西北工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TN304.2

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6 徐凌燕;CdZnTe晶體中的深能級缺陷及其對光電性能的影響[D];西北工業(yè)大學(xué);2014年

7 李巖;碲鋅鎘晶片高效低損傷加工工藝的研究[D];大連理工大學(xué);2010年

相關(guān)碩士學(xué)位論文 前10條

1 潘松海;鋁誘導(dǎo)CdZnTe多晶薄膜的制備及物理特性研究[D];北京化工大學(xué);2013年

2 張興剛;CdZnTe半導(dǎo)體探測器電極研究[D];西北工業(yè)大學(xué);2006年

3 伍順發(fā);CdZnTe晶體分離結(jié)晶界面形狀計算及穩(wěn)定性分析[D];重慶大學(xué);2008年

4 李輝;采用壓縮坩堝自由空間方法提高CdZnTe晶體性能的研究[D];上海大學(xué);2012年

5 陳繼權(quán);CdZnTe晶體歐姆接觸薄膜電極的制備工藝與性能研究[D];西北工業(yè)大學(xué);2004年

6 陳俊;CdZnTe晶體的表面處理和鈍化研究[D];四川大學(xué);2006年

7 孫金池;Cu/Ag合金薄膜用作CdZnTe探測器電極的研究[D];西北工業(yè)大學(xué);2005年

8 李鋒;CdZnTe探測器在X射線熒光分析中的應(yīng)用研究[D];國防科學(xué)技術(shù)大學(xué);2005年

9 文錦雄;常重力條件下分離結(jié)晶法制備CdZnTe晶體的全局數(shù)值分析[D];重慶大學(xué);2012年

10 黃平;利用88-100keV能區(qū)CdZnTe能譜測定鈾富集度[D];中國原子能科學(xué)研究院;2003年

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