晶格應變對氮化鋁半導體磁性影響之研究

烏采結構的三族金屬氮化物為具有新穎磁性的光電材料，為瞭解在氮化鋁中晶格應變對其磁性的影響，本研究以快速熱退火處理方式調變氮化鋁晶格應變，利用X-ray繞射儀、EDX、PL以及拉曼光譜分析其晶格結構，探討熱退火處理方法對氮化鋁晶格結構所引起的變化。結果顯示氮化鋁為高品質烏采晶型的多晶薄膜，EDX分析顯示在不同退火溫度條件下，會使N/Al比例改變，但是比值都大於1，即樣品的氮（N）原子百分比均大於鋁（Al）原子百分，說明樣品中存在原子空缺，Al原子空缺數應多於N原子空缺數；由樣品的PL光譜可得知與Al原子相關之空缺為VAl2- 或VAl3-的型態，電性量測結果顯示樣品均為高阻值特性。藉由Williamson-Hall plot分析法得知在不同退火溫度條件下，熱退火處理會使氮化鋁晶格結構的應變變小，同時影響晶粒尺寸；由拉曼量測顯示氮化鋁晶型沒有發生明顯的變化，但是晶格結構中應變的變化會造成聲子結構的改變，其A1（LO）峰值呈現與應變相依的變化，而E2（high）、 E1（TO）與A1（TO）峰值均往高頻偏移。振動樣品磁力計（VSM）量測磁性結果發現，氮化鋁樣品在室溫時具有明顯的磁滯曲線，熱退火處理會使其飽和磁化強度減少，然而飽和磁化強度變化的趨勢與N/Al比例的關聯並不明顯，但是和晶格應變量的減少較為一致。其中未退火處理的氮化鋁有最高的飽和磁化強度為20.3 emu/g，殘留磁化強度為0.4 emu/g，矯頑磁場為140 Oe；以1000oC退火處理的氮化鋁，其矯頑磁場則可增至257 Oe。根據BMP（束縛極化子）理論模型得知，晶格應變與束縛極化子的形成有關，我們推測應變量大的晶格可能有較高的形變能量，以致提高束縛極化子間耦合作用因此造成較大的飽和磁化強度。因此影響烏采結構氮化鋁（wz-AlN）磁性的主要機制，可藉由陽離子空缺所引發磁矩的理論模型說明，我們推測由晶格應變場引發的束縛極化子理論模型也是傳遞磁交換交互作用的重要媒介。

關鍵字

氮化鋁薄膜；晶格應變；離子空缺；磁性；束縛極化子

並列摘要

The novel magnetic properties of the group III-Nitrides with Wurtzite structure have made AlN the most serious candidates for the Spintronic devices and magneto-optoelectronic materials. In this thesis, we report the lattice strain effect on the magnetism of AlN semiconductors. The lattice strain of AlN crystals were modulated by Rapid Thermal Annealing (RTA) and ion-implant methods. The lattice structures were characterized by X-ray diffraction spectroscopy (XRD), Energy-Dispersive X-ray spectroscopy (EDX), photoluminescence (PL) and Raman spectroscopy analysis. The qualities of AlN thin films can be identified by XRD measurements and the results show that AlN samples studied here are polycrystalline thin films with Wurtzite structure. The N/Al mole ratio estimated from EDX are greater than 1 for AlNs under different RTA conditions and ion-implant treatments. The existence of Al vacancies can be demonstrated by PL measurements, and can be characterized by VAl2- and VAl3- types. Additionally, AlN shows a high resistivity by measurements. The strain of AlN samples decreases by annealing process and ion-implant treatment by the results of Williamson-Hall Plot analysis. Raman analysis show that the AlN samples are Wurtzite structures under the treatments. There is clear relationship between A1（LO）phonon mode and lattice strain. Moreover, E2（high）、 E1（TO）and A1（TO） modes show blue shift after annealing. The ferromagnetic properties-dependent saturation magnetization, Ms, was performed with vibrating sample magnetometer (VSM) at room-temperature. All samples show apparent hysteresis loops. The value of Ms, Mr and coercive fields (Hc) can be identified by their M-H curves. It clear reveals that Ms decreases with the decreases of the lattice strain, but there is no clear direct relationship between and Ms and N/Al mole ratio. The Ms, Mr and Hc for AlN are about 20.3 emu/g, 0.4 emu/g and 140 Oe, respectively. The Hc for AlN sample under 1000oC treatment is 257 Oe. According to the Bound Magnetic Polarons (BMP) theory, the formation of BMP is related to the lattice strain. The increase strain energy is favorable for coupling among BMP and result in higher Ms. Therefore, this work suggest that the ferromagnetic properties in AlN polycrystalline thin films origin in both the cation vacancies and BMP models.

並列關鍵字

AlN ； Strain ； Ion vacancies ； Magnetic ； Bound Magnetic Polaron

參考文獻

[44]郭昱賢，“利用XRD分析成長於不同緩衝層/基板之氮化銦特性”，碩士，國立台北科技大學，2011。

[13]劉昇旭，“氧化鋅摻雜釩之粉末合成與磁電結構特性研究”，碩士，國立成功大學，2005。

[37]Vanni Lughi and David R. Clarke, Applied Physics Letters, 89, (2006) 241911.

[26]Y.-R. Wu, M. Singh, and J. Singh, “Lateral and vertical charge transport in polar nitride heterostructures: Applications for HEMTs, novel vertical junction and Sensors”, C. Wood and D. Jena, Eds., Springer-Verlag New York, (2007) pp. 111-159.

[1]H. Li et al., “Copper-doped AlN polycrystalline powders: A class of room-temperature ferromagnetic materials”, Solid State Communications, Vol. 151, (2011) 499-502.

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晶格應變對氮化鋁半導體磁性影響之研究

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