Positron Annihilation Lifetime Spectroscopy (PALS) Technique y-detection:scintillator photomultiplier Time between positron penetration and it's annihilation in a sample is measured 3-6x106 are accumulated in a spectrum Mathematics dn(t) =-入n(t)】 n(0)=1 probability n(t)that e+is alive at time t: dt A-positron annihilation rate 10 Siw=219p时 Positron lifetime spectrum in bulk: GaAs Zn 230 ps 10 n(t)=e hbuu! : 102 slope of the exponential decay .m 10 人bwk I bulk 100 200 300 400 1n-1---1- Channels PDF文件使用"pdfFactory”试用版本创建iw.fineprint.cn
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Positron Trapping Potential positive charge Rydberg states neutral due to negative charge negative charge X Attractive potential mainly due to missing ion(repelling core is absent) in semiconductors:additional Coulomb tails (1/r->rather extended) PDF文件使用"pdfFactory”试用版本创建w,fineprint..cn
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Physics bulk one-defect trapping model trapping rate K trapping annihilation from bulk with入，=1/rbs-1 1 trapping to vacancy-defect with K s-1 annihilation from the defect with=1/d annihilation two-component lifetime spectrum N(t)=I/t exp(-t/)+12/t2 exp(-t/t2) 10 。 g8A3t=350p5t=280ps GaAs:Zn 230 ps ■Information vacancy type (mono-,di-,vacancy cluster) tawv=∑lt 2-reflects the electron density defect concentration C 10 K=- 11 ≈C 100 200 300 400 Channels PDF文件使用"pdfFactory”试用版本创建iw.fineprint.cn
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Positron Lifetime Spectra 106 ◆ positron lifetime spectra consist of As-grown Cz Si exponential decay components Plastically deformed Si ◆ positron trapping in open-volume defects leads to long-lived components 105 longer lifetime due to lower electron density T2=320ps ■ analysis by non-linear fitting:lifetimes r;and (divacancies) intensities I 104 ◆ positron lifetime spectrum: N0= T3=520ps =218ps (vacancy 103 clusters) trapping coefficient (bulk) : 图司 2 3 5 Time [ns] trapping rate defect concentration PDF文件使用"pdfFactory”试用版本创建iw.fineprint.cn
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目前正电子寿命谱的状况 PAL谱仪在1980s中期完全定型， ■采用BaF,闪烁体是PAL谱仪的一次重要 革新 存在的关键问题： 寿命谱的分辨极限； BaF,闪烁体和光电倍增管的老化.， PDF文件使用"pdfFactory”试用版本创建品.fineprint.cn
目前正电子寿命谱的状况 n PAL谱仪在1980s中期完全定型. n 采用BaF2闪烁体是PAL谱仪的一次重要 革新. n 存在的关键问题: 寿命谱的分辨极限; BaF2闪烁体和光电倍增管的老化. PDF 文件使用 "pdfFactory" 试用版本创建 3www.fineprint.cn 33