- 學位論文
α相碘化汞電性及輻射偵測特性分析
Electrical Characterization And Radiation Spectroscopy Analysis of α-HgI2 Crystals
摘要
本文利用物理蒸汽傳輸法成長α相碘化汞(α-HgI2)晶體並進行其電性及輻射偵測特性的研究。在晶體成長方面，利用提高晶體成長溫度(~112℃)後，可獲得有清楚成長刻面、透光性良好的晶體。在電性量測方面，於I-V特性曲線觀察到暫態電流(transient current)的現象。藉由I-t特性量測，得到不同溫度、固定偏壓下電流隨時間衰減的情形，我們將此行為歸因於塊材內電場的鬆弛(relaxation)及缺陷中心捕捉電荷的釋放(detrapping)過程。此外，利用一拉長型指數衰減函數與單純指數衰減函數疊加可對此行為得到良好的描述，並經由擬合計算得到一系列關係到釋放時間的衰減時間常數τ1、τ2；其中Type 2晶體於偏壓10 V下所得到的τ2遵循熱活化的結果，經由作Arrehnius plot擬合計算得到活化能Et2 = 290 ± 80 meV。另一方面，在電場垂直碘化汞c軸的情況下，由暗電導率隨溫度的變化求得四類晶體的活化能Ea介於1.1 ~ 1.3 eV之間，並加以討論。最後，輻射偵測特性量測的結果顯示本實驗室所成長之碘化汞晶體品質已達到可偵檢計數的等級；但於多頻道分析頻譜中未得到241Am應有的峰值，此可歸因於晶體內部缺陷密度仍然過高及所謂的”極化效應(polarization effect)”。
並列摘要
In this report, electrical characterization and radiation spectroscopy of α-HgI2 crystals grown from vapor phase are studied. By improving the temperature of crystal growth up to 112℃, the as-grown crystals are transparent and have clear facets. From the I-V curve, we observe the result of transient current. And by the I-t measurement, we obtain that current decay with time under bias. This decay may be due to the relaxation of electric field in the bulk and the detrapping of charges trapped by the trapping centers. Furthermore, the I-t curve can be fitted with the superposition of a stretched exponential decay function and a single exponential decay function. The decay time constants, τ1 andτ2 , relate to the detrapping time is evaluated. But only in the case of Type 2 crystal under bias 10 V, the time constant τ2 shows the result from thermal active mechanism. By Arrehnius plot, the activation energy Et2 = 290 ± 80 meV is evaluated. In another way, from the temperature dependence of dark conductivity of crystals for different type, the activation energy Ea is evaluated of about 1.1 ~ 1.3 eV. Finally, the radiation spectroscopy indicate that crystals grown in our laboratory achieve counter level.