- 學位論文
氮化鋁薄膜特性分析及應用於研製紫外光偵測器之研究
Study of AlN Deposition and the Application for UV Detectors
摘要
本論文之目的是在藍寶石(sapphire)基板上低溫成長氮化鋁(AlN)薄膜，探討不同基板溫度下之薄膜品質，並應用氮化鋁材料良好光電特性研製平面式金屬-半導體-金屬結構紫外光偵測器。 實驗中，利用Helicon迴旋濺鍍系統低溫成長厚度為1μm之氮化鋁薄膜，利用晶像結構分析(XRD)、薄膜表面形貌分析(AFM)與穿透率量測(Transmittance measurement) ，分析不同基板溫度之薄膜特性。在研究中，與AlN(4000Å)/Sapphire比較，厚度為1μm之AlN薄膜因厚度增加使的累積的應力也越大(晶格不匹配度，12%)，晶像結構與表面粗糙度皆受其影響，並且未能得到薄膜品質與基板溫度的明顯關係。而AlN(1μm)/Sapphire仍具長高排向(002)、高平整度(~1nm)之特性，於晶格轉動曲線(Rocking curve)量測中也可得低半高寬值(~1°)。穿透率量測，AlN薄膜於長波段具有高穿透性，並且於波長200nm處促降為零，皆為顯示AlN薄膜良好的結構特性。藉由穿透率並可推得AlN薄膜於基板溫度450℃下，具有最大光學能隙值6.16 eV，十分接近文獻的理論值(6.2eV) 。 氮化鋁金屬-半導體-金屬光偵測器是用In situ metallization製程，於Sapphire基板低溫300℃成長AlN薄膜後，直接濺鍍金屬鋁做為指叉電極。元件具有低的暗電流，因指隙大小暗電流大小在191~795 fA之間，與目前文獻上具最低暗電流以MOCVD沉積AlN製作的MSM元件十分接近，說明了Helicon所成長氮化鋁的品質是相當優異的。使用150W氘燈照射元件，光暗電流接近於兩個order的差距，且光電流與入射光功率呈線性關係。在響應頻譜量測中，元件在入射光波長為200nm具有最大響應度為3.65×10-6 A/W，其響應波段與推導所的光學能隙吻合，並與長波段響應度有兩個order的差距，顯示所製作之氮化鋁金屬-半導體-金屬光偵測器具有良好的波段判別能力，適合深紫外光之偵測。
並列摘要
In this thesis, AlN thin film grown on c-sappire using Heclion sputtering system in low temperature(300~500℃)，and in application to fabricated the AlN metal-semiconductor-metal(MSM) photodetector. There were correlations of AlN thin film crystalline, surface morphology and transmittance characteristic measured by XRD, AFM and photospectrometer. In XRD θ-2θ scan, rocking curve and AFM measurement, AlN(1μm)/sapphire with relatively poor performance compared with AlN(4000Å)/Sapphire. It attributed to the great stress between AlN and Sapphire based on the large lattice mismatch of 12%, the stress effect more serious with thicker film growth. After all, AlN(1μm) still exhibit apparent c-axis preferred-oriention growth on c-sapphire, and low R.M.S roughness about of 1nm. And with low FHWM value in rocking measurement. In transmittance, it found that AlN exhibit high transmission in long wavelength(500~800nm), and decay abruptly in the wavelength of 200nm, it also indicate the great quality of AlN thin film. The best optical bandgap of 6.16 eV which very closed to the theoretical value of AlN Bulk can be calculation from the transmittance spectrum of the AlN thin film which exhibit best transmission with substrate temperature of 450℃ AlN MSM device were fabricated on AlN/Sapphire with the low temperature of 300℃, exhibit a low dark current between 191~795 fA with different electrode spacing. The dark current of the photodetectors in this thesis is closed to the AlN MSM devices fabricated by MOCVD in reported literatures, indicating the excellent quality in the AlN film growth. The photo/dark current ratio of the devices shows almost 2 orders of magnitude with the illumination of D2 lamp, and the relationship between photo current and light power is in good linearity. The peak responsivity of 3.65×10-6 A/W at the wavelength of 200nm and larger about 2 order than the responsivity at wavelength of 400nm, it consisting with the optical bandgap calculation and reveal the good selection ability of wavelength. According to the result, AlN MSM devices are suitable for deep UV detectors.