金屬有機前驅物－－三甲基銦對氮化銦磊晶薄膜之光電及化學特性影響

Investigation of Trimethylindium Flow Rate on Electro-Optical and Chemical Properties of InN Epilayer Grown on GaN/Al2O3 Substrate

III-V族化合物半導體是目前發光二極體元件的主要材料，其中氮化銦具有許多優異光電特性，其窄光學能隙（0.65 eV）是III-V族氮化物材料延伸至紅外光區的重要特性之一。由於大多數的氮化銦都是以金屬有機化學氣相沉積製備，然而金屬有機前驅物（三甲基或三乙基）中含碳氫氧等元素，使得材料在成長過程中造成元素的摻雜而影響了其光電特性，因此本研究以三甲基銦為三族前驅物，並以金屬有機分子束磊晶系統成長氮化銦薄膜，同時進行其化學組態、雜質元素與光電特性之相關性分析，以了解金屬有機前驅物對成長氮化物之影響。由二次離子質譜儀與X光光電子光譜儀結果發現，前驅物三甲基銦中的碳與氫會隨著製程中摻入InN薄膜，其濃度會隨著三甲基銦流量增加而增加。相反地，薄膜中的氧含量會隨著三甲基銦增加而減少。並且在InN表面有高濃度的碳、氫與氧雜質，因此當表面經過HCl蝕刻後，V/III~1.81所成長之InN薄膜的電子濃度由5.57×1019 cm-3降至3.31×1019 cm-3、遷移率則由192 cm2/V-s提升至335 cm2/V-s。光學性質部分透過光激發螢光光譜得知，近能帶邊緣放射訊號會隨著V/III流量比增加而藍移是因為Burstein-Moss effect，而高電子濃度大部分是氮空缺與雜質元素所貢獻，因此高載子濃度是造成光學吸收限藍移的主要原因。另外可知，三甲基銦前驅物在製程中會間接提高載子濃度，並影響光電特性。 III-nitride is important material for high power light emitting diode(LED) devices. Specially, InN has attracted the most attention among the III-V nitrides because of its noticeable narrow band gap(0.65 eV) , small effective mass and high electron mobility. Due to most InN fi lms were prepared by MOCVD. However, metal-organic precursor often included carbon, hydrogen and oxygen. Therefore, we discussed the chemical and electro-optical properties of InN fi lms grown on MOCVD-GaN lyaer with different trimethylindium fl ow rate. The InN fi lms were characterized by secondary ion mass spectrometry, X-ray photoelectron spectroscopy photoluminescence and Hall effect. InN films were grown on MOCVD-GaN/Al2O3 substrate by plasma-assisted metal-organic molecular beam epitaxy. Secondary ion mass spectrometry and X-ray photoelectron spectroscopy results showed that carbon and hydrogen of trimethylindium precursor were incorporated during InN fi lms growth. Also, the C and H concentrations increase with increasing trimethylindium fl ow rate. On the other hand, the oxygen concentration decreases with increasing trimethylindium flow rate. A relatively high C, H and O concentration exists near the surface of the InN film. Therefore, before etching, the fi lm exhibits the high carrier concentration of 5.57×1019 cm-3 and low mobility of 192 cm2/V-s. After etching, the etched InN fi lm exhibited a decreased carrier concentration of 3.31×1019 cm-3, increased electron mobility of 335 cm2/V-s. Optical properties showed that the PL spectra exhibited blue-shift with increasing V/III flow ratio due to the Burstein-Moss effect. However, high carrier concentration was measured probably due to nitrogen vacancies and impurity contributed. Therefore, blue shift of the optical absortion is caused by high carrier concentration.