為了改善a-IGZO載子遷移率無法提升的問題，所以利用高溫退火處理來使IGZO結晶化(Crystallization)，但直接退火處理所形成的結晶IGZO4為多晶相，且晶粒小而產生晶界(Grain boundary)使晶相雜亂。為了解決結晶IGZO4晶相雜亂的問題，本研究以從優取向(Preferred orientation)結晶化的方法做前瞻性的研究。以AZO作為緩衝層，藉由AZO的C軸從優取向使IGZO在退火處理的長晶過程中，可以沿著AZO的從優取向成長，使結晶IGZO4也具有C軸取向，藉此改善晶相雜亂的問題。
從結果中得知a-IGZO在退火溫度800°C時，IGZO開始成長IGZO4結晶；IGZO4結晶隨著退火處理溫度上升持續成長。結構方面從TEM可以看到IGZO退火溫度1000°C持溫一小時後的結晶IGZO4；C軸方向結構是由一層InO2和一層GaZnO2交替堆疊而成，a-b兩軸方向是由InO6形成的六邊形(Hexagonal)結構，但非正六邊形。IGZO/AZO退火溫度1000°C持溫一小時後的結晶IGZO4；C軸方向結構一樣是由一層InO2和一層GaZnO2交替堆疊而成，但在C軸方向的InO2層狀間距有晶格變動(Change of lattice)的現象；a-b兩軸方向的InO6形成正六邊形結構
，且InO6中的In離子在a-b兩軸方向間距與AZO的Zn離子在a-b兩軸方向間距趨近相同。此證明在退火處理的長晶過程中，以AZO作為緩衝層，可使結晶IGZO4在a-b兩軸方向平行沿著AZO的a-b兩軸方向成長。IGZO/AZO的IGZO4晶粒明顯比IGZO的IGZO4晶粒還要更大，證明AZO緩衝層在退火處理過程中，有助於IGZO4結晶的成長。
在光電性質方面，從實驗發現隨著IGZO4結晶的成長，會使最大透射率波段逐漸藍移(Blue shift)。IGZO/AZO的透射率(Transmittance)相較於a-IGZO/AZO在黃紅光波段約下降6%，且在藍紫光波段的透射率則大幅上升14%，然而IGZO/AZO的可見光平均透射率仍有80%以上。具有C軸取向的結晶IGZO4可見光平均透射率比a-IGZO高了3.2%。IGZO/AZO的IRO2對比IGZO有稍微下降，說明AZO緩衝層可以減少晶界的亞晶格(Subgrain)產生。在能帶(Band)結構方面，IGZO/AZO的能隙對比IGZO明顯變小。因導電帶邊緣的滲透傳導(Percolation conduction)效應，使載子遷移率會隨著載子濃度增加而上升，而AZO作為緩衝層有助於IGZO4結晶的成長，改善了結構上的缺陷並降低了電阻率、提升了載子濃度，使載子遷移率上升。

High temperature annealing is adapted to improve the carrier mobility of a-IGZO. The crystalline IGZO4 can be observed after annealing, and the crystal phase is disordered due to the small grains and grain boundaries. In order to solve the disorder of crystalline IGZO4, AZO is used as buffer layer in this study. IGZO can be grown along the c-axis preferred orientation of AZO in the annealing process, and hence the crystalline IGZO4 can have c-axis orientation.
The results show that IGZO layer begin to grow crystalline IGZO4 when；the a-IGZO at annealing temperature of 800˚C. From the TEM images, the crystalline IGZO4 can be observed after annealing at the temperature of 1000˚C for one hour, and its c-axis orientation structure is formed by alternating the stacks of InO2 layer and GaZnO2 layer. The lattice constant of the InO2 layer in the c-axis orientation is also changed InO6 in the a-b plane can be observed to be a regular hexagonal structure, and In ion of InO6 has the same spacing in the a-b direction as the Zn ion of AZO in the a-b direction. In the annealing process, AZO buffer layer causes the a-b axial direction of the crystalline IGZO4 to grow parallel along the a-b axis of the AZO. The grain size of IGZO4 for IGZO/AZO specimen is significantly larger than that of IGZO specimen, and it proves that the AZO buffer layer contributes to the growth of IGZO4 crystal in the annealing process.
For electrical and optical properties, the blue shift of the maximal transmittance is observed with the growth of crystalline IGZO4. The transmittance of c-IGZO/AZO is 6% higher than that of a-IGZO/AZO, in the yellow-red light region, and it is also 14% higher in the blue-violet light region. The transmittance of IGZO/AZO for specimen the average visible light is above 80%. The average visible light transmittance of c-axis orientation crystal IGZO4 is 3.2% higher than that of a-IGZO specimen. The IRO2 of IGZO/AZO specimen is lower than that of IGZO specimen, indicating that the AZO buffer layer can reduce subgrains generation of grain boundaries. For band structure, the band gap of IGZO/AZO specimen is significantly smaller than that of IGZO specimen. Percolation conduction effect at the conduction band edge causes the increase in carrier mobility and carrier concentration. AZO buffer layer contributes to the growth of IGZO4 crystal, which can improve the structure defects and reduces the resistivity and increase the carrier mobility and carrier concentration.

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