雙加熱氣相沉積系統成長低溫高載子遷移率的氮化鎵薄膜特性研究

Abstract

本論文使用自組式雙加熱氣相沉積(MOCVD)系統成長氮化鎵薄膜，在低磊晶溫度850℃下成長變上加熱溫度(Ceiling temperature, Tc)系列樣品，並利用霍爾量測、變溫霍爾量測、X光繞射與光激螢光光譜對氮化鎵薄膜的電學與光學特性進行分析。 變上升溫系列中，上加熱溫度從850℃提高至1150℃並與傳統磊晶條件(無上加熱溫度)比較，從霍爾量測發現在上加熱溫度為1050℃時，氮化鎵薄膜的載子遷移率與載子濃度分別為515 cm2/Vs與5.1x1016 cm-3。為了進一步釐清影響氮化鎵薄膜載子遷移率的散射機制，而進行X光繞射實驗與變溫霍爾量測實驗。從X光繞射頻譜得知差排密度並未隨上加熱溫度改變有明顯變化，約在3.5x108 cm-2到4.5x108 cm-2之間，顯示差排密度並未受到上加熱溫度影響而提升薄膜品質。透過變溫霍爾實驗，載子遷移率在低溫區間與T3/2呈現線性關係，而高溫區間與T-1/2呈現線性關係，推測影響氮化鎵薄膜載子遷移率的主因為本質缺陷散射造成。

In this theses, we use the home-made two heater MOCVD reactor to grow low-growth temperature GaN thin films at 850℃. The electrical and optical properties of the samples were investigated by Hall, Temperature dependent Hall, X-ray diffraction and photoluminescence measurements. Hall measurement results indicate that the optimized ceiling temperature of GaN thin film is 1050℃ in ceiling temperature series. The carrier mobility and carrier concentration of GaN thin film is 515 cm2/Vs and 5.1x1016 cm-3.The X-ray diffraction and temperature dependent Hall measurement are employed to confirm the scattering mechanism. The X-ray diffraction spectra shows that the dislocation density doesn't change with the various ceiling temperature, implying that the dislocation density won't affect by ceiling temperature and improve thin film quality. The temperature dependent Hall measurement indicates carrier mobility is linear relationship with T3/2 in low temperature measurement region and linear relationship with T-1/2 in high temperature measurement region, and we speculate that the native defects scattering dominate the carrier mobility.