氮化鋁之濺鍍沉積探討及其光電應用

The Investigation of Sputtering Deposition of AlN and its Optoelectronic Applications

陳美汝(Meei-Ru Chen)

指導教授 ： 高慧玲

中原大學/工學院/電子工程研究所/博士(2014年)

https://doi.org/10.6840/cycu201400707

摘要

本論文利用迴旋濺鍍系統，成功的以300-500℃的低溫直接在藍寶石基板上沉積AlN磊晶薄膜，探討AlN之成長機制及分析其結晶品質，並在AlN薄膜上研製金屬-半導體-金屬紫外光偵測器及評估元件之性能。
在AlN薄膜結晶品質方面，透過X光繞射檢測薄膜為c軸從優取向，並以φ方向掃描及TEM電子繞射圖驗證為單晶結構；其(0002)面X光擺動曲線的半高寬值會隨基板溫度增加而由0.94°降至0.58°，由此可推論薄膜品質會隨溫度增高而提升；薄膜之表面粗糙度則使用原子力顯微鏡觀測及估算，其表面粗糙度的均方根值僅為0.6-0.7 nm，顯示薄膜表面平整度甚佳，非常適合用於研製表面聲波元件。AlN對藍寶石基板之晶格不匹配度雖高達13.3%，但於本研究中但仍可成功的以低溫濺鍍達到磊晶之結果，本論文引用區域匹配磊晶(DME)模型及TEM影像來解釋AlN之成長機制；由觀察TEM之明視野及暗視野影像則可估算AlN薄膜的差排密度約為10^10 cm^-2，尚能符合光電元件之需求。藉由低溫CL 量測之螢光光譜亦可觀察到AlN能隙邊緣躍遷為6.33 eV，與其能隙理論值(6.2 eV)很接近，可再次證實AlN薄膜具有良好之磊晶品質。
於AlN 金屬-半導體-金屬紫外光偵測器的效能評估方面，本研究中不同電極指隙設計的紫外光偵測器，其暗電流最高僅為795 fA，非常接近以MOCVD法研製的最佳AlN金屬-半導體-金屬元件之暗電流值，顯示本研究以低溫沉積的AlN薄膜品質甚佳。另以暗電流所推算之元件理想因子及蕭特基能障各為1.03及1.01 eV，此數值顯示元件的蕭特基接觸品質甚好。在紫外光照光實驗中，元件的光暗電流比值接近兩個數量級，可知元件對紫外光感測能力甚佳，其光電流與入射光功率並且呈現線性關係，此線性特性即顯示本論文的紫外光偵測器已達實用水準。光頻譜響應實驗中，於波長200 nm處有最大響應度，由此證實元件可吸收光能量與AlN能隙相當之深紫外光，並激發最大的光響應度。元件於波長200 nm與可見光的光響應度差距約為兩個數量級，顯示元件對深紫外光與可見光之分辨能力頗佳。綜合以上結果，本研究之AlN 金屬-半導體-金屬元件極適合應用於深紫外光之偵測。

關鍵字

氮化鋁 ； 低溫沉積 ； 迴旋濺鍍系統 ； 磊晶 ； MSM紫外光偵測器 ； 頻譜響應

並列摘要

In this study, Aluminium Nitride thin films have been deposited directly on sapphire substrates at low temperatures (300-500℃) by a helicon sputtering system. The structural quality of AlN films was characterized by X-ray diffractometry and transmission electron microscopy (TEM). The full-width at half maximum (FWHM) of the (0002)-AlN rocking curve decreases with the growth temperature and is ranged within 0.58°-0.94°. The result suggests that the quality of the AlN films can be improved by increasing temperature. The films exhibit smooth surface with root-mean-square roughness as small as 0.6-0.7 nm evaluated by atomic force microscope. Even though the lattice-mismatch between AlN and sapphire is as high as 13.3%, the AlN epitaxial films have been obtained. The single crystalline characteristics of AlN film were confirmed by X-ray φ-scan reflection and SAD patterns of TEM. The growth mechanism of this large lattice-mismatched system can be explained by using the domain matching epitaxy (DME) model and the fourier-filtered image of the interface of AlN/sapphire. The dislocation density of about 10^10 cm^-2, which is low enough for optoelectronic applications, was calculated from the bright-field and dark-field TEM images of the sample. The band-edge transition (6.30 eV) of AlN film close to its theoretical value of energy bandgap was observed in the cathodoluminescence spectrum.
The metal-semiconductor-metal (MSM) photodetectors were fabricated on AlN/sapphire with various electrode spacing and were analyzed by the I-V characteristics. The low dark current of the AlN MSM devices was about 795 fA biased at 20V and was close to that of the best AlN MSM device fabricated by MOCVD in the reported literature, indicating the good quality of our AlN films. The ideality factor of 1.03 and effective Schottky barrier height of 1.01 eV derived from the dark current, reveal a good quality of Schottky contacts. The ratio of the photocurrent to dark current is more than two orders of magnitude with the radiation of the D2 lamp, showing fairly good sensitivity to the deep UV light. It is noted that the photocurrent increases almost linearly with the incident optical power. The linearity of the photoresponse is essential for photodetectors. The spectral response of the device displays the peak responsivity at 200 nm and a UV/visible rejection ratio of about two orders of magnitude.
The results of this low temperature deposition suggest the feasibility of epitaxial growth of AlN on sapphire substrates and the incorporation of the AlN films in optical devices at deep ultraviolet region.

並列關鍵字

helicon sputtering system ； Aluminum nitride ； low temperature growth ； epitaxial growth ； spectral responsivity ； MSM UV photodetector

參考文獻

[49] 陳弘修，“以迴旋濺鍍法沉積氮化鋁薄膜及其矽摻雜之研究”，中原大學碩士論文，民國101年。

[51] 莊子毅，“直流濺鍍高品質氮化鋁薄膜之物理與光學特性研究分析”，中原大學碩士論文，民國101年。

[4] J. Li, Z. Y. Fan, R. Dahal, M. L. Nakarmi, J. Y. Lin, and H. X. Jiang, “200 nm deep ultraviolet photodetectors based on AlN”, Appl. Phys. Lett., vol. 89, p. 213510, 2006.

[5] J. Jasinski, Z. Liliental-Weber, Q. S. Paduano, and D. W. Weyburne, “Inversion domains in AlN grown on (0001) sapphire”. Appl. Phys. Lett., vol. 83, p. 2811, 2003.

[6] Y. A. Xi, K. X. Chen, F. Mont, J. K. Kim, C. Wetzel, E. F. Schuberta, W. Liu, X. Li, and J. A. Smart, “Very high quality AlN grown on (0001) Sapphire by metal-organic vapor phase epitaxy”, Appl. Phys. Lett., vol. 89, p. 103106, 2006.