以原子層沉積系統成長鎵摻雜氧化鋅薄膜做為電流擴散層應用於氮化鎵系列發光二極體

本文使用 ALD 成長 n-type ZnO-based 薄膜，探討其做為透明導電膜 (TCO) 的能力。結果顯示，ZnO 薄膜在180℃的成長溫度下，可獲得最低電阻率6.5 × 10−3 Ω-cm。其對應的載子 (電子) 濃度與遷移率分別為3.37 × 1019 cm−3 以及28.56 cm2/V-s。而在摻雜 Ga 後的 ZnO 薄膜 (GZO)，更可大幅降低電阻率。在成長溫度325℃下成長的 GZO 薄膜，有最低電阻率4.39 × 10−4 Ω-cm，其載子 (電子) 濃度與遷移率分別為1.19 × 1021 cm−3 與11.9 cm2/V-s。在光學特性方面，ZnO 的光能隙約為3.276 eV，GZO 的光能隙約為3.631 eV。兩者在可見光波段 (400–700 nm) 皆有大於80%的高穿透率。尤其是在藍光波段 (450 nm) 更有超過95%的極高穿透率。將 GZO 薄膜應用到藍光 LED 當電流擴散層後，可以發現，與使用 ITO 做為電流擴散層的藍光 LED 相比。在注入電流20 mA 時，兩者有相似的 VF ~3.1 V。而且，在 GZO 薄膜與 ITO 薄膜兩者厚度相近時，GZO 有更低的片電阻。這導致GZO的電流擴散能力要高於 ITO，能獲得更好的功率效率。使用 GZO 的藍光 LED 功率效率為17.25%，優於使用ITO的功率效率16.77%。這些數據顯示，GZO 有極大的潛力能取代 ITO，成為藍光 LED 的透明導電膜。另外，在350℃的成長溫度下，GZO 薄膜在紫外光波段 (370 nm) 有較高的穿透率。且經過300℃氮氣環境下5分鐘的熱退火後，其在370 nm 的穿透率更能從84%上升到88%。在365 nm 的穿透率也能從80% 上升至86%。而電特性也不會因此劣化 (~5 × 10−4 Ω-cm)。因此，將其做為透明導電膜與內部導線，應用到紫外光 LED 上，以探討陣列式 LED (LED array) 是否能改善出光功率。經過與廣域式 (broad-area) LED 的比較後，可發現陣列式 LED 的最大光輸出功率密度為7.25 W/cm2以及可持續到90 mA 後才開始衰減。優於最大光輸出功率密度只能到1.34 W/cm2 以及在70 mA 後就開始衰減的廣域式 LED。結果表明，使用陣列式的 LED 對於 UV 區域的光輸出功率有顯著改善。

關鍵字

原子層沉積系統；氧化鋅；氧化鎵鋅；氮化鎵；發光二極體

並列摘要

In this dissertation, the potentiality of n-type ZnO-based thin films grown by ALD as transparent conductive oxide (TCO) was investigated. The results show that the minimum resistivity of ZnO film is 6.5 × 10−3 Ω-cm at a growth temperature of 180℃. The corresponding carrier (electronic) concentration and mobility are 3.37 × 1019 cm−3 and 28.56 cm2/V-s, respectively. Furthermore, the Ga-doped ZnO thin film (GZO) can reduce the resistivity significantly. The minimum resistivity of GZO film is 4.39 × 10−4 Ω-cm at growth temperature of 325℃, and their carrier (electronic) concentration and mobility are 1.19 × 1021 cm−3 and 11.9 cm2/V-s, respectively. In terms of optical characteristics, the optical band gap energy of ZnO is ~3.276 eV and the optical band gap energy of GZO is ~3.631 eV. The ZnO and GZO thin films exhibit the average transmittance over 80% in the visible spectra (400–700 nm), especially higher than 95% at 450 nm blue wavelength. After applying the GZO thin film to a blue LED as a current spreading layer, the characteristics of LEDs with GZO film are compared with those of LEDs with ITO film. The results show that when the injection current is 20 mA, they have similar VF ~ 3.1 V. Moreover, when the thickness of both the GZO film and the ITO film is similar, GZO has a lower sheet resistance. This results in the current spreading capability of GZO is higher than ITO. Thus, the GZO thin film has better power efficiency. The power efficiency of the blue LED with GZO is 17.25%, which is better than the power efficiency of the blue LED with ITO 16.77%. These data show that GZO has great potential to replace ITO as a transparent conductive film for blue LEDs. In addition, at a growth temperature of 350℃, the GZO film has a high transmittance in the ultraviolet wavelengt (370 nm). Furthermore, after 5 minutes of thermal annealing at 300℃ under nitrogen, the transmittance at 370 nm increased from 84% to 88%. The transmittance at 365 nm can also be increased from 80% to 86%. Moreover, the electrical characteristics are not deteriorated (~5 × 10−4 Ω-cm). Therefore, it is used as a current spreading layer and an internal wire to be applied to an ultraviolet LED to investigate whether an LED array can improve the optical power. After comparison with broad-area LEDs, it can be found that the maximum light output power density of the LED array is 7.25 W/cm2 and it can only begin to decay after it reaches 90 mA. It is better than a broad-area LED with a maximum optical output power density that can only reach 1.34 W/cm2 and start to decay after 70 mA. The results show that the use of array-type LEDs has a significant improvement in light output power in the UV region.