低溫氮化鎵薄膜磊晶與物理特性之研究

Abstract

本論文中使用自組式雙加熱有機金屬化學氣相沉積(MOCVD)系統成長氮化鎵(GaN)薄膜，在低磊晶溫度850 ℃下成長變五三比(V/III)系列樣品，並利用霍爾量測、X光繞射以及光激螢光光譜，對於薄膜的電學與光學特性進行分析。 在變五三比系列中，V/III ratio從7500增加至20000，從霍爾量測得知GaN薄膜之最佳V/III ratio為10000，此時的載子濃度與載子遷移率分別為3.9x1018 cm-3以及146 cm2/Vs，而低溫(19K)光激螢光光譜亦為近能帶邊緣發光主導。為了進一步釐清影響GaN薄膜載子遷移率的主要散射機制，進行X光繞射與變溫霍爾量測實驗，探討不同散射機制的影響性。從X光繞射頻譜得知差排密度並未隨著V/III ratio改變有明顯變化，約在2.0x109到4.9x109 cm-2之間，顯示差排散射並非影響低溫GaN薄膜載子遷移率的主因。透過變溫霍爾實驗，量測載子遷移率隨溫度變化與T-1/2呈現線性關係，推測影響低溫GaN薄膜載子遷移率的主因為本質缺陷散射。

In this theses, we use the home-made two-heater MOCVD reactor to grow low-growth temperature(850 ℃) GaN (LT-GaN) thin films. The electrical and optical properties of these samples were investigated by Hall, X-ray diffraction and photoluminescence measurements. Hall measurement results indicate that the optimized V/III ratio of LT-GaN thin films grown by two-heater MOCVD reactor is 10000. The carrier concentration and carrier mobility of LT-GaN thin films is 3.9x1018 cm-3 and 146 cm2/Vs. The LT-photoluminescence (19 K) result shows that the emission is dominated by near band emission. The X-ray diffraction and temperature dependent Hall measurement (TD-Hall measurement) are employed to confirm the scattering mechanism. The X-ray diffraction spectra show that the dislocation density does not change significantly with the various V/III ratios, implying that the dislocations scattering is insignificant in V/III series of GaN films. The TD-Hall measurements indicate that the native defects scattering is the dominated scattering mechanism.