雙加熱有機金屬氣相沈積系統成長 p 型氮化鎵薄膜電特性之研究

Abstract

本論文使用自組式雙加熱有機金屬氣相沈積系統(MOCVD)成長 p 型氮化鎵薄膜,主要探討在不同成長溫度(Substrate Temperature, Ts) 以及不同上加熱溫度(Ceiling Temperature, Tc)下對於薄膜品質的影響, 並利用霍爾量測、X 光繞射、光激螢光光譜以及電中性原理進行 p 型 氮化鎵薄膜電學及光學特性分析。 變成長溫度系列中,基板溫度從 1000oC 降至 725oC 並與傳統磊 晶條件(無上升溫系統)比較,從霍爾量測發現加入上升溫系統 1150oC 後,整體阻值可維持~2.69 Ω-cm 至基板溫度 800oC,且藉由 X 光繞射 半高寬發現在低成長溫度下差排密度始終小於傳統條件約 1.5 倍。 為了釐清上升溫系統對於何種補償以及散射中心的影響,後續在低基 板溫度下成長了變上加熱溫度系列樣品,利用室溫霍爾量測搭配電中 性原理估算並發現補償濃度隨上加熱溫度有接近 50 倍的變化,約 4.5x1018cm-3 到 1x1017cm-3。接著利用光激螢光光譜觀察此系列樣品黃 光帶歸一強度與上加熱溫度之關係,發現在未開啟上升溫系統時黃光 帶強度約為開啟時的 1000 倍,推測上升溫系統提供腔體上方一穩定 熱場成功改善了傳統 MOCVD 系統中三族前驅物(TMGa)在低溫成長 時,因氣相溫度不足導致 TMGa 分子裂解不完全所引起的大量碳雜 質溶入問題。

In this thesis, we use the home-made Two-Heater MOCVD reactor to grow p-type GaN thin film. We aim to investigate the effects of substrate temperature(Ts) and ceiling temperature(Tc) on the films quality. The electrical, structure and optical quality were analyzed by Hall measurement, Charge neutrality principle, X-ray diffraction and Photoluminescence measurement. In the substrate temperature varied series, Two-Heater mode (T.H.) Tc is fixed at 1150oC and Ts was designed to decrease from 1000oC to 725oC compared with the Conventional mode (Conv.). We find that the resistivity can maintain 2.69Ω-cm until Ts=800oC and the dislocation density are always 1.5x smaller than Conv. samples. In the ceiling temperature varied series, Ts is fixed at 800oC and Tc is changed from 650oC to 1150oC. We found that density of compensating donor has near 50x decrease from 4.5x1018cm-3 to 1017cm-3 and the normalized intensity of yellow emission(2.2eV) has also decrease more than 1000x with higher Tc. Therefore, we speculate that the ceiling temperature can provide a high temperature zone in upper chamber for III-precursors to crack more efficiently, hence less carbon impurity will incorporate in films.