三族氮化物金屬-半導體-金屬紫外光偵測器之製作及特性研究

Fabrication and Characterization Study of Ⅲ-Nitrides Based Metal-Semiconductor-Metal UV Detectors

許志祥(Chih-Hsiang Hsu)

指導教授 ： 高慧玲

中原大學/工學院/電子工程研究所/碩士(2009年)

https://doi.org/10.6840/cycu200900976

摘要

本論文利用三族氮化物中具有良好光電特性之氮化鋁及氮化鎵材料研製平面式金屬-半導體-金屬結構紫外光偵測器，並探討其特性。 氮化鋁金屬-半導體-金屬光偵測器是用In-situ metallization 製程，利用低溫迴旋濺鍍法在分別在藍寶石基板與氮化鎵/藍寶石基板上沉積之氮化鋁，再直接濺鍍金屬鋁作為電極金屬，製作成不同主動區厚度、圓形電極與不同指隙之指叉電極，來探討元件結構對於元件效能的影響。 當基板為藍寶石時，主動區厚度為4000Å之元件，暗電流為6.96pA，而厚度為1μm(此元件基板為p-GaN)之元件暗電流低到6.49pA，說明主動區厚度對於元件的影響，磊晶厚度越厚，品質越佳。非對稱之圓形電極可以有效的降低暗電流，提高光暗電流比，在面積比1:40時，光暗電流比值達到最大29.4，為面積比1:10的9.51倍。氮化鋁金屬-半導體-金屬光偵測器之暗電流的大小，依指隙的不同在52~3.78pA之間，相較於同樣以濺鍍法沉積氮化鋁製作金屬-半導體-金屬元件之文獻，其暗電流的值約少了五個order，說明了氮化鋁的品質是相當不錯的。當使用150W氘燈照射元件，光暗電流可達兩個order的差距，且光電流與入射光功率呈線性關係，顯示所製作之氮化鋁金屬-半導體-金屬光偵測器，適合深紫外光之偵測。 在氮化鎵金屬-半導體-金屬光偵測器中，將GaN/Sapphire基板經過稀鹽酸表面處理，放入迴旋濺鍍系統濺鍍金屬鋁作為指叉電極。在偏壓10V時，以指隙的不同，暗電流的大小12.6~137pA之間。並針對指寬指隙設計，提升元件效能，入射光He-Cd　雷射強度為0.0414mW，隨著指隙的不同，響應度在0.1168~0.1575A/W之間，與目前文獻上最好的p-GaN MSM元件響應度相比，同樣有著很好的響應度，且元件之光電流與入射光功率在大指係的情況下呈現不錯的線性度，證明所製作之氮化鎵MSM 元件非常適合當紫外光偵測器。使用Kr-F pulse雷射入射，元件的響應速度會隨著指隙變大、外掛電阻加大，而變慢，但對於偏壓的改變並不明顯。以外插法計算，可推得實際的上升時間，並計算元件之頻寬可得在工作偏壓20V，指寬、隙皆為4μm時，得到最大的頻寬為19.5MHz。

關鍵字

迴旋濺鍍法 ； 氮化鋁薄膜 ； 氮化鎵薄膜 ； 金屬-半導體-金屬元件

並列摘要

In this thesis, Ⅲ-nitride materials, GaN and AlN, which uniquely present at the same time the excellent electronic and optoelectronic properties, were employed to fabricate the metal-semiconductor-metal (MSM) photodetectors for UV detection.
AlN films were deposited on sapphire substrates as well as GaN/sapphire using helicon sputtering with growth temperature of 300℃. Al metal was in-situ deposited on AlN, right after the AlN film growth, to fabricate the electrodes of MSM UV photodetectors. Various thickness of absorption layer and different patterns of metal electrodes were employed to investigate the effects on the performance of photodetectors.
The AlN(4000Å) MSM photodetectors on sapphire substrates show the dark current of 6.96pA. The AlN(1μm) MSM photodetector on p-GaN substrates, show a lower dark current of 6.49pA. It indicates that larger thickness and smaller lattice mismatch between substrate and absorption layer can improve the quality of AlN films, and thus the performance of the photodetectors. Asymmetrical circle electrodes can suppress dark current and upgrade photo current. The area ratio of 1:40 results in a photo/dark current ratio of 29.4, which is 9.51 to that of the area ratio 1:10. In different finger spacing, dark current is between 3.78 and 52pA in AlN MSM photodetectors. Dark current become smaller by increasing finger spacing. The dark current of the photodetectors in this thesis is five orders of magnitudes less compared to reported literatures, indicating the excellent film quality in the AlN film growth. The photo/dark current ratio of the device shows more than 2 orders of magnitude with the illumination of D2 lamp, and the relationship between photo current and light power is in good linearity. According to the results, AlN MSM devices are suitable for UV detection.
The GaN MSM devices show dark current of 12.6-137pA at 10V bias for different finger spacing. Changing the design of finger width and spacing, we can increase the device responsivity. For 0.0414mW He-Cd laser illumination, the device responsivity between 0.1168 and 0.1575A/W with various finger spacing were obtained. The results are among one of the best in the reported literature. The relationship between photo current and laser power is linear when using larger finger spacing. The measured bandwidth of 19.5MHz at bias 20V were obtained by the real rise-time extrapolation, which may be limited by the measurement facility.

並列關鍵字

GaN thin film ； MSM ； Helicon sputter ； AlN thin film

參考文獻

[1] Cinzia Caliendo, “Gigahertz-band electroacoustic devices based on AlN thick films sputtered on Al2O3 at low temperature”, Appl. Phys. Lett., Vol. 83, No. 23, 2003.

[2] K. Uehara, C. –M Yang, T. Shibata, S. –K. Kim, S. Kameda, H. Nakase and K. Tsubouchi, “Fabrication of 5-GHz-Band SAW Filter with Atomicaly- Flat-Surface AlN on Sapphire”, IEEE Ultra. Sym., vol. 1, 2004.

[3] C. Caliendo, P. Imperatori, “High-frequency, high-sensitivity acoustic sensor implemented on AlN/Si substrate”, Appl. Phys. Lett., vol. 83, No. 8, 2003.

[5] Lung-Chien CHEN, Ming-Song FU and In-Lin HUANG, “Metal- Semiconductor-Metal AlN Mid-Ultraviolet Photodetectors Grown by Magnetron Reactive Sputtering Deposition”, J.J.Appl.Phys., Vol.43, No. 6A, 2004.

[8] M. A. Khan, J. N. Kuznia, D. T. Olson, J. M. Van Hove, M. Blasingame, L. F. Reitz, “High-responsivity photoconductive ultraviolet sensors based on insulating single-crystal GaN epilayers”, Appl. Phys. Lett., Vol. 60, p2917 (1992).