以有機金屬化學氣相磊晶法研製Ⅲ-Ⅴ族氮化物半導體材料特性與光電元件之研究

本論文的主旨是以有機金屬氣相沈積法所成長之高品質氮化鋁鎵厚膜為主，並利用氮化銦鎵/氮化鎵形成之多重量子井發光二極體光電特性加以分析；此外，論文亦探討氮化鎵材料中摻雜鎂或矽之薄膜沈積於不同層數之氮化鋁/氮化鎵緩衝層於矽基板上並分析其光電與材料相關特性。高品質之氮化鋁鎵是白光光源重要的組成材料之一，但由於氮化物基板之一為藍寶石基板技術最為成熟，因此成為侷限住高品質氮化物主要的瓶頸，特別在於厚膜的含鋁氮化物材料中。當鋁含量增加時其臨界厚度隨之減少，伴隨著超過臨界厚度即造成薄膜的差排產生，在元件的製程上產生極大的問題，為改善此一問題帶來的影響，本論文利用氮化鎵的兩階段成長法，成功的將氮化鋁鎵材料之臨界厚度提昇且不破裂之薄膜，提供一個有效的白光光源緩衝層成長方式，並可在一般以氮化鎵材料吸光問題上獲得改善的方法。為瞭解氮化鋁鎵薄膜品質良窳，並比較氮化鎵孕核層﹑氮化鋁孕核層﹑高溫氮化鎵緩衝層﹑低溫氮化鋁應力緩衝層等結構對氮化鋁鎵材料的影響，論文中利用紫光發光二極體沈積在所設計結構上來驗證，在材料品質驗證上主要以雙晶繞射X-Ray量測不同反射面，例如對稱面(0002), (0004), (0006),以及非對稱面( ) 及( )等平面之半高寬，並比較出所設計之樣品中最佳成長條件與結構，其中以氮化鋁鎵成長於氮化鎵孕核層之品質最好，另外由光激致光得到多層量子井中在不同成長溫度下具有不同銦含量組成與二次離子質譜分析材料的縱深具相同的結果，其次利用陰極致光觀察所設計之結構缺陷密度的比較，並且由穿透式電子顯微鏡的觀察輔助說明了相關結構缺陷上的不同。在紫光二極體方面，利用變溫電流-電壓量測粹取出二極體之理想因子與串聯電阻等參數，接著利用電容-電壓量測粹取出量子井中相關載子分佈及量子井寬度，在室溫變電流電激致光量測中粹取出二極體的波長藍移特性來自於量子井中壓電效應，而變溫電激致光量測觀察到的紅移是來自於焦爾熱效應。此外，氮化鎵成長於矽基板亦是本論文的研究重點，矽基板與氮化鎵晶格差異約有-16%，aSi(111)=0.3840 nm及aGaN=0.3189 nm的差異造成氮化鎵需承受來自於矽基板的拉應力，此外在此異質接面上不同的熱膨脹係數(GaN = 5.59x10-6 K-1, Si = 2.61x10-6K-1)造成磊晶層容易破裂，氮化鋁是最佳的應力緩衝層的選擇之一，雖可降低裂紋得到較佳品質的氮化鎵，但距離商業化仍需要克服前述的兩個問題，因此應力在此系統中亟待解決，本論文設計以不同對數的氮化鎵/氮化鋁來觀察結構應力變化情形，以釐清低溫緩衝層如何釋放氮化鎵與矽基板間的應力。首先由雙晶繞射X-Ray對稱面(0002), (0004), (0006),以及非對稱面( ) 及( )等反射面來檢驗氮化鎵分別摻雜鎂及矽原子之磊晶層，成長於不同對數的緩衝層上之磊晶品質變化，並藉由寬角度的繞射粹取出氮化鎵晶格變化，進而分析隨氮化鎵/氮化鋁對數的增加其磊晶成長方向上的晶格明顯增加，由掃瞄式電子顯微鏡及穿透式電子顯微鏡觀察所成長的樣品中氮化鎵/氮化鋁經由緩衝層可以降低穿透式差排的形成，樣品經由室溫及變溫光激致光觀察發現隨著氮化鎵/氮化鋁對數變化使表面的氮化鎵晶格常數變化使能隙受到雙軸壓力的影響而產生了能帶的變化，此外經由室溫下拉曼量測亦發現隨氮化鎵/氮化鋁對數增加應力明顯變緩的趨勢，而根據上述的觀察應力及晶格常數的變化，對未來發展高亮度發光二極體運用在矽基板上一個有力的參考。

關鍵字

氮化鎵；氮化鋁鎵；矽基板；發光二極體；穿透式電子顯微鏡

並列摘要

This dissertation discusses on a thick and crack-free AlGaN film that is deposited on a sapphire substrate by using metal-organic chemical vapor deposition (MOCVD) technology. A violet LED is used that InGaN/GaN multiple quantum wells (MQWs) are deposited on this AlGaN template. The properties of the violet LED are investigated on the basis of material properties and by carrying out measurements such as electrical and optical measurements. Another object, the GaN:Si and GaN:Mg films grown on different pairs, is studied. In addition, the properties of the GaN/AlN buffer layer are presented in this paper. High-quality AlGaN is fabricated on deep ultraviolet (DUV) materials for general illuminance. However, a nitride-based material is usually used with sapphire as the substrate which lack high quality nitride films cause by large lattice mismatch generates high density of dislocation from interface in this system. Especially, an AlN film as nucleation layer (NL) deposited on sapphire following GaN film usually contents dislocation density as high as order to 108~1010 cm-3. Consider, for example, an AlGaN film on GaN template whole Al content increases with decreasing ternary film thickness. The thick Al0.1Ga0.9N film grown on the sapphire substrate may generate a crack when the thickness of the film is greater than 0.1 m. Such a crack in the film will degrade the device performance. For solving this problem, we investigate AlGaN grown directly on GaN nucleation layer (NL) by using a two-step growth method. A thick and crack free of AlGaN film whose exceeds 1.7 m is obtained. By using this method, we introduced an effective buffer for growing the white LEDs. Furthermore, the high absorption of GaN at 365 nm can be suppressed by the thick AlGaN buffer. In order to investigate the quality of the AlGaN film, we compare the GaN NL, AlN NL, and HT-GaN templates, and insert an LT-AlN film for the growth of a thick AlGaN film on sapphire. The crystalline quality of AlGaN templates and device characteristics of violet LEDs fabricated from the AlGaN templates are investigated. XRD patterns of GaN (0002), (0004), and (0006), and of asymmetrical GaN (10-15) are used for studying the violet LEDs grown on the NL and templates and for indentifying the crystallite quality. The photo-luminescence indicated MQWs at different growth temperatures with different Indium content. With respect to the dislocation density, the images of cathode- luminescence (CL) showed that AlGaN on a GaN NL had a low dislocation density. Finally, high-resolution transmission electron microscopy (HR-TEM) showed that the thick AlGaN film with a GaN NL had better crystallite quality. In the case of the devices used of violet LEDs measurements, the ideal factor and series resistance of the diodes are estimated on the basis of the temperature dependence of the current-voltage measurement. In order to design MQWs, the capacitance-voltage (C-V) characteristics of all LED structures were measured by using an Agilent 4294A precision impedance analyzer at 100 kHz. Knowledge of the C-V characteristics in the zero-bias depletion region can be of further assistance in the estimation of the doping concentration of barrier and the thickness of the undepleted p-GaN layer. This in turn would lead to the optimization of the thickness of the MQWs and p-GaN layer. Furthermore, power dependent electroluminescence is examined for the LEDs in order to observe emission peaks that exhibit a little blue shift because of the screening effect of the piezoelectric field in the QWs. The temperature dependence of electroluminescence indicated a redshift caused by the Joule heating. GaN can be grown on foreign substrates, for example, GaAs and Si. But, the primary considertion how to growth a lattice mismatch material up to 16 % between GaN and Si substrate, is the requirement for the growth of a high quality film. In general, the lattice between aSi(111) = 0.3840 nm and aGaN = 0.3189 nm is under strongly tensile strain in the case of a GaN film deposited on a Si substrate. In addition, cracks are formed when the growth temperature cools down to the room temperature when the thermal expansion coefficient for GaN = 5.59 × 10–6 K–1, and that of Si = 2.61 × 10–6K–1. AlN is the most commonly used material to avoid such cracks. This method can efficiently suppress cracks and facilitate the growth of a high quality GaN film. However, for commercial application, the first requirement is how to improve the difference in the internal quantum efficient (IQE) of GaN base LEDs on silicon substrate than on sapphire substrate. However, the GaN/AlN relaxation mechanism remains unknown. We investigated GaN:Si and GaN:Mg grown on multiple pair (MP) GaN/AlN buffer layers and verified the residual strain at the top of the GaN with a Si or Mg dopant. By using this method, we examined the strain relaxation in a GaN film on a Si system. First, two sets of samples are investigated by using high resolution X-ray diffraction patterns of the /2θ scans of the symmetrical GaN (0002), (0004), and (0006), and the asymmetrical (10-12), and (10-15) planes. The increase in the number of pairs led to an increase in AlN lattice c more than the GaN. The cross sectional of SEM and TEM images also indicated that an increase in the MPs resulted in a decrease in the top GaN dislocation density. Futher, the energy band gap toward the narrow band gap due to the biaxial strain increased because of the temperature dependence of the photoluminescence peak and the increase in the MPs. The Raman measurement indicates that the GaN strain decreases with an increase in the MPs, which in turn induces GaN under a strain relaxation.

並列關鍵字

GaN ； AlGaN ； Si wafer ； Light-emitting diode ； TEM

參考文獻

[1] I. Akasaki, “Key inventions in the history of nitride-based blue LED and LD”, J. Crys. Growth 300, 2–10 (2007)

[2] J. Wu W. Walukiewicz, S. X. Li, R. Armitage, J. C. Ho, E. R. Weber, E. E. Haller, Hai Lu William J. Schaff, A. Barcz and R. Jakiela, “Effects of electron concentration on the optical absorption edge of InN”, Appl. Phys. Lett. 84, 2805 (2004)

[3] O Ambacher, “Growth and applications of Group III-nitrides”, J. Phys. D: Appl. Phys. 31 2653–2710 (1998)

[4] Y. Taniyasu, M. Kasu, T. Makimoto, “Threading dislocations in heteroepitaxial AlN layer grown by MOVPE on SiC (0 0 0 1) substrate”, J. Crys. Growth 298, 310–315 (2007)

[5] Y. Taniyasu, M. Kasu, T. Makimoto, “An aluminium nitride light- emitting diode with a wavelength of 210 nanometres”, Nature 441, 325 (2006)

國際替代計量

以有機金屬化學氣相磊晶法研製Ⅲ-Ⅴ族氮化物半導體材料特性與光電元件之研究

主題瀏覽