使用酸性礦化劑進行氨熱法合成氮化鎵晶體之研究

Abstract

氮化鎵在藍綠光二極體與雷射二極體的光電運用上，已成為具吸引力的材料之一，氮化鎵光電元件目前是採用磊晶的方式在異質基材上沉積薄膜，也由於缺乏同質基材的緣故，使得鍍膜產生了無法避免的缺陷，裂化了元件的性質與壽命，所以開發氮化鎵同質基材是必然的趨勢，而氨熱法長晶在此方面具高度的發展性。 本實驗中，使用三種不同的酸性礦化劑(NH4Cl、NH4Br、NH4I)，並且在不同的溫度下進行長晶，將鎵、礦化劑及液態氨溶劑密封於壓力釜中，施加溫度及壓力至液態氨的臨界點之上，此時為超臨界流體，此狀態下鎵與礦化劑作用而形成中間產物，中間產物分解之後析出氮化鎵晶體，實驗結果顯示，NH4Cl可在低溫下合成出氮化鎵晶體，相較於其他礦化劑，NH4Cl較具活性可以促進氮化鎵合成，從SEM來看，氮化鎵晶體由許多的奈米顆粒所聚集而成，XRD顯示，酸性礦化劑所合成的氮化鎵，都有出現兩種晶體結構，NH4Cl較易形成六方晶結構，而NH4Br、NH4I較易形成立方晶結構。

GaN have been an attractive material for optoelectronic applications in blue-green light emitting diodes and blue laser diodes due to there excellent property. GaN thin film deposited on heterogeneous substrates bring a drawback in film quality because of lack of GaN substrates. The ammonothermal method is a potential method to synthesize high quality single crystal of GaN for homogeneous substrates. GaN were synthesized by ammonothermal using three kinds of acid mineralizer (NH4Cl、NH4Br、NH4I) at different process temperature. Precursor (gallium), solvent (ammonia) and mineralizer were sealed in the autoclave. The solvent can be brought to supercritical fluid by increasing temperature and pressure above critical point of solvent. Gallium dissolved in supercritical ammonia to form gallium-containing intermediates and then intermediates converted to crystalline phase of GaN. As the result, using NH4Cl as a mineralizer can synthesize GaN at lower temperature. It seems to be more effect to form GaN compared to other acid minerlizers. In SEM, it shows agglomerate GaN composed of nanoparticales. Depending on XRD, Both wurtzite structure and zinc-blende structure were obtained in ammonothermal synthesis. Using NH4Cl favors wurtzite GaN while using NH4Br and NH4I favor zinc-blende GaN