氧化鋅及二氧化錫光電性質之研究

Abstract

本論文分為兩部分，第一部分為熱門的II-VI 族半導體材料氧化鋅，吾人使用原子層沉積技術(Atomic layer deposition, ALD)成長高品質的氧化鋅做為晶種層，藉此增加基材的導電性，並使得電化學沉積的氧化鋅晶柱有較佳的結晶品質與結晶優選方向。藉由XRD、SEM、PL分析，探討不同電鍍參數，以及熱處理對結晶品質及顯微結構的影響，從而找出結晶品質最佳的電鍍參數。第二部分為透明導電膜二氧化錫之研究，將二氧化錫薄膜上蒸鍍鋁，在不同溫度或時間下進行熱擴散，製備p型導電薄膜。 第一部份為電化學沉積氧化鋅。首先，先藉由循環伏安法，獲得沉積氧化鋅的工作電位，必須要高於-1.2 V(相對於Ag/AgCl參考電極)。接著固定其他參數，分別探討在施加不同過電位、過氧化氫濃度、溫度的影響，XRD分析顯示在-0.95 V、過氧化氫濃度10 mM、80 oC時，具有最大的晶粒尺寸，為50.4 nm。接著探討晶種層的熱處理及電鍍後的熱處理之影響。以ALD成長的氧化鋅晶種層若不退火，由XRD半高寬和PL強度可以得知結晶品質大幅下降，電鍍後退火對晶體品質有改善。XRD及PL兩項分析皆顯示兩段式製程:-1.4 V持續10秒，接著-0.8 V持續5分鐘，可以比一段式製程:-0.8 V持續5分鐘，得到更高結晶品質的氧化鋅。 第二部分為二氧化錫的導電膜的製備，二氧化錫的導電薄膜可以藉由將鋁熱擴散進入二氧化錫薄膜製備而成，在霍爾效應量測中顯示二氧化錫導電薄膜是p型，並且只有在600 oC進行擴散，時間1到2小時，擴散完畢將表層的鋁以稀鹽酸酸蝕後才能得到。比較二氧化錫摻雜鋁在600oC下擴散，以不同轉速塗佈溶膠，以旋轉塗佈轉速4000 rpm均較轉速3000 rpm者具有較佳的電性及穩定性。在旋轉塗佈轉速4000 rpm時，於600 oC擴散兩小時，電洞濃度為3.33x1020 cm-3，載子遷移率為1.24 cm2/V•s，電阻率為0.03 Ω• cm；於600 oC擴散1小時後鹽酸酸蝕者，電洞濃度較高達4.05x1020 cm-3，載子遷移率為0.794 cm2/V•s，電阻率為0.0251 Ω•cm。吾人以此方法製備的二氧化錫之電洞濃度較現今多數文獻高兩個數量級。在製備完成後90天的期間，每30天進行霍爾效應的量測，結果顯示，無論是載子濃度、載子遷移率，電阻率都是穩定的值，顯示此薄膜電性的穩定性相當好。

The contents can be divided into two topics. In the first topic, high quality ZnO films were grown by atomic layer deposition (ALD) as seedlayer on sapphire substrates. Afterwards, the main layer of ZnO was prepared by electrodeposition. The effect of different electrodeposition parameters (applied voltage, precursor concentration, temperature ) and thermal treatment on crystalline quality and microstructures were investigated by XRD, SEM, PL analysis. In the second topic, the p-type conductive oxide, SnO2:Al was investigated. After incorporating Al as dopants into SnO2, the deposited films were annealed at various temperatures for different durations. The p-type conductive films of a high hole concentration and low resistivity were achieved. In the first topic on electrodeposition of ZnO, the potentials at which ZnO can be plated from a specific electrolyte were determined by using cyclic voltammetry. Experimental results indicate that ZnO films can be plated at potentials higher than -1.2 V(vs. Ag/AgCl) .The largest crystal size was 50.4 nm, obtained at the electrodeposition condition of -0.95 V, 10 mM H2O2 and 80 oC. Rapid thermal annealing (RTA) on seedlayer, and the post-deposition RTA treatment after electrodeposition can enhance the crystal quality. The XRD and PL analysis indicated that better ZnO crystal can be obtained by two-step electrodepostion . In the second topic, the p-type conductive SnO2:Al thin films were prepared by the thermal diffusion of Al on SnO2 thin films on glass substrate. Hall measurements revealed that the SnO2:Al films exhibited long-term stable p-type conductivity at a specific diffusion temperature of 600 oC .The p-type SnO2:Al films with a high hole concentration (4.05x1020 cm-3) and a low resistivity (0.0251 Ω•cm) was obtained.