鎂、銦摻雜氮化鎵冷激光光譜與躍遷時間之研究

Abstract

本論文利用超快雷射激發鎂、銦摻雜氮化鎵薄膜，藉量測其時間累積與時間解析冷激光譜，探討未摻雜與摻雜試片躍遷時間之改變，並且以不同激發強度量測其時間累積之激發光譜變化。實驗中以冷激光光譜探討摻雜對光譜半高寬之影響 ; 並且以超快嚮應光電倍增管(μcpPMT)量測不同摻雜與波長之躍遷時間演進。對於未摻雜之氮化鎵，我們量到其低溫下近帶間躍遷之生命期約在100到250ps之間，與目前已發表文獻的結果相近。在低溫下以20 MW/cm2之超快雷射激發時，位於365nm之電漿(Electron Hole Plasma, EHP)躍遷出現，隨激發能量增加而大幅增加其強度且顯示有紅位移(red shift)。另外在微量銦摻雜氮化鎵之時間累積光譜發現近能帶躍遷(near band edge emission, NBE)之半高寬較未摻雜之氮化鎵有變窄的趨勢，且需50 MW/cm2之雷射激發才會出現同位置之EHP。室溫下量測銦摻雜氮化鎵時，入射強度高於25 MW/cm2即出現EHP。對於鎂摻雜氮化鎵之室溫時間累積光譜與連續冷激光譜(CWPL)之觀測發現鎂相關之躍遷在超快雷射激發下幾乎消失，而低溫下卻由鎂相關之躍遷主導。

In our study, we used a TRPL system and to measure the decay time of undoped GaN. The decay time for near band edge (NBE) is a few hundreds of picoseconds and consists with the reported data. We observe the EHP at 365 nm for undoped GaN at low temperature above 20 MW/cm2 excitation energy whose intensity superlinearly increases with excitation energy. In time-integration photoluminescence (TIPL), the FWHM of NBE emission of In-doped GaN is smaller than that of undoped GaN. The In-doped GaN inhibits EHP unless excited by 50 MW/cm2, which is reduced to 25 MW/cm2 at room temperature. For Mg doped GaN, we found that the Mg related transitions are much weaker in TIPL spectra than in CWPL spectra, but these transitions dominate the TIPL spectra at low temperature.