不同氣體環境熱處理氧化鋅緩衝層對共濺鍍薄膜特性影響之研究

A study of the ZnO buffer layer annealed under various atmosphere and its effect on the post-deposition cosputtering films

莊翔鈞(Chuang Hsiang chun)

指導教授 ： 劉代山

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/碩士(2008年)

摘要

本研究利用射頻磁控共濺鍍系統沉積氧化鋅緩衝層，再以不同氣體環境(氧氣、氮氣、氫氣)熱處理，以改善氧化鋅緩衝層內部之結構缺陷。研究結果顯示，各種不同氣體環境熱處理氧化鋅緩衝層之XRD，其氧化鋅緩衝層優先成長方向(002)，皆隨著熱處理溫度上升，繞射峰值越趨於明顯，半高寬值(FWHM)變小而晶粒大小也隨熱處理溫度上昇而變大；在熱退火500oC時，以氧氣熱處理氧化鋅緩衝層之(002)繞射峰值為最明顯，氮氣熱處理之氧化鋅緩衝層次之，氫氣熱處理之氧化鋅緩衝層為最低。而在氧化鋅緩衝層薄膜之應力，因為熱退火提供足夠的能量，使薄膜內之應力鬆弛，其影響為使薄膜由壓應力至張應力；以氫氣熱處理氧化鋅緩衝層之張應力為最高，氧氣熱處理次之，氮氣熱處理氧化鋅緩衝層為最低。
不同氣體環境熱處理氧化鋅緩衝層之PL量測，可觀察到有紫外光區域(UV emission)與綠光區域(green emission)；而影響紫外光區強弱為薄膜之結晶性，隨著熱處理溫度上升各氧化鋅緩衝層結晶性逐漸增強而造成紫外光區域增強；而綠光區域之強弱為氧缺位(Vo)影響為主因，由於氫氣熱處理為增加氧缺位，因此氫氣熱處理氧化鋅緩衝層有最大相對峰值；而氧氣熱處理為填補氧缺位(Vo)，因此綠光區域之相對峰值為最弱；由上述研究結果可知，不同氣體環境熱處理之氧化鋅緩衝層，其結晶性隨著熱處理溫度越高其優先成長方向(002)之繞射峰值越強而晶粒也越大；氧化鋅緩衝層之應力，隨著熱處理溫度升高，皆由壓應力逐漸轉換成張應力，以氫氣熱處理之氧化鋅緩衝層為最明顯；而由PL量測可知，紫外光區域亦隨著不同氣體環境熱處理溫度升高而越趨於明顯；而綠光區域以氫氣熱處理之氧化鋅緩衝層峰值為最大。
氧化銦錫薄膜(ITO)沉積於不同環境熱處理氧化鋅緩衝層上，可有效提升載子濃度；因為氧化鋅緩衝層增加氧化銦錫薄膜薄膜內部In2O3(222)之結晶性，而導致載子濃度增加。ITO-ZnO共摻雜薄膜沉積於不同環境熱處理氧化鋅緩衝層則逐漸降低載子濃度；原因為氧化鋅緩衝層與ITO-ZnO共摻雜薄膜為同質結構，且氧化鋅緩衝層有抑制雜質(Sn)摻雜作用，因此載子濃度下降，以氮氣熱處理最明顯。
室溫下濺鍍AlN-ZnO 共濺鍍薄膜於不同氧化鋅緩衝層上由電特性可知，以氮氣熱處理氧化鋅緩衝層載子濃度下降最多，此原因為氧化鋅緩衝層有抑制雜質摻雜作用，且以氮氣熱處理結晶性為最佳，因此載子濃度下降最多，其次為氫氣與氧氣熱處理。而經過氮氣熱處理400oC之AlN-ZnO 共濺鍍薄膜，其導電形態並無轉換成穩定p型導電型態，原因為氧化鋅緩衝層增強了AlN-ZnO 共濺鍍薄膜內部氧化鋅之結晶特性，且抑制了沉積AlN-ZnO 共濺鍍薄膜時之AlN之含量，而導致無法順利轉換。

關鍵字

氧化鋅薄膜,氧化鋅緩衝層,熱退火

並列摘要

In this study, the ZnO bufferl layer were grown on Si(100) substrate by the reactive RF magnetron sputtering. In addition,the annealing at 300oC to 700 oC under oxygen(O2), nitrogen(N2) and Hydrogen(H2) respectively. That were improve the ZnO buffer layer internal structure defects.
The result of study, the X-ray diffraction peak angles of ZnObuffer layer with (002) orientation as a function of annealing temperature. That the high thermal annealing has the effects of narrowing the diffraction peak, indicating that grain growth has occurred. The stress in ZnO buffer layer changes from compressive to tensile with the increase of room temperature to 700 oC.The ZnO buffer layer obtainsthe tensile stress quantity for to be highest at annealing under Hydrogen environment.
The Photoluminescence spectra have two bands of luminescent peaks. One band is located in the range of UV and violet light. The other band consisted of green luminescence. The thin film crystallinity is affects the UV emission intensity the main reason. The various ZnO buffer layer crystallinity gradually strengthens along with the heat treatment temperature rise to bring about the UV emission region enhancement.
The green luminescence of ZnO is related to oxygen vacancies(Vo). Therefore has the highest relative peak value by the hydrogen heat treatment ZnO buffer layer, Because hydrogen heat treatment for increases the oxygen vacancy(Vo).Because oxygen heat treatment for decrease the oxygen vacancy(Vo), so that has the lower relative peak value by the hydrogen heat treatment ZnO buffer layer.
We report a buffering method of improving the quality of ITO thin flms on Si by r.f. magnetron sputtering. By applying a ZnO buffer before the ITO deposition in the same run of sputtering.Room-temperature Hall effect measurements showed that a increase of carrier density and decrease of mobility.It is evident to argue that increasing the ITO crystallinity is one way to increase the free carrier concentration since, with a more crystalline structure, there will be increased Sn solubility and less scattering centers. The slightly increased carrier concentration may come from the increased Sn solubility in In2O3 matrix.
Indium zinc oxide (IZO) thin films at atomic ratios Zn：In at.33 % were doping on the ZnO buffer layer by rf cosputtering system at room temperature using indium tin oxide (ITO) and zinc oxide (ZnO) targets.We can observe increased the X-ray diffraction peak angles of Indium zinc oxide (IZO) doping on ZnO buffer layer with (002) orientation as a function. The carrier concentration decrease of Indium zinc oxide (IZO) thin films on ZnO-buffer Si comes from the drastic improvement of the crystal structure. It will be to restrain ITO co-doping to enter Indium zinc oxide (IZO) thin films.
In addition, AlN codoped ZnO thin films on the ZnO buffer layers by the reactive RF magnetron sputtering. To investigate the effect of homo-buffer layer on the crystallinity of N–Al codoped ZnO films, XRD analysis exhibit high preferential orientation of (002) plane, indicating their good crystallinity and the value of full-width at halfmaximum (FWHM) of the N–Al codoped film is much lower, so that grain growth has occurred. AlN codoped ZnO thin films grown with the buffer layer has a much lower carrier concentration and a higher carrier mobility than that without buffer layer. The results indicate that the ZnO film grown with buffer layer has fewer defects which act as donors. The introduction of buffer layer can suppress evidently the generation of defects and dislocations derived from the large lattice mismatch and the difference of thermal expansion coefficients between ZnO and substrate.

並列關鍵字

ZnO thin film,ZnO buffer layer,annealing

參考文獻

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