以時間解析飛秒光譜研究摻碲銻化銦的超快動力學

Abstract

本論文以時間解析飛秒光譜研究摻碲銻化銦之超快動力學，透過改變樣品之環境溫度及激發光之能量密度，我們可藉由瞬時反射率的變化(□R/R)得到不同溫度及激發光能量密度下之電子-聲子能量弛緩時間，並根據雙溫模型計算電子-聲子耦合常數。電子-聲子耦合常數與自由電子的濃度有關，自由電子可藉由環境的熱能激發至傳導帶，而增加激發光的能量密度同樣地也會增加自由電子的濃度。此外，透過變溫的霍爾實驗及電阻量測，我們證明高摻雜濃度的銻化銦在傳輸性質上具有金屬的特性，然而接近本質的銻化銦其電導率或電阻率在170 K附近出現金屬絕緣相變的現象。本論文也進行變溫的紅外反射光譜量測，而電漿邊緣隨溫度的改變有紅移及藍移的現象。若依據Drude-Lorentz 模型擬合紅外反射光譜，則可得到電漿頻率，進而計算電子的等效質量、電子的動量散射時間及電子-聲子耦合常數。 藉由時間解析激發-探測顯微儀，我們能在固定溫度梯度的PANTEC熱電元件上進行不同位置的時間解析光譜掃描，且在特定位置增加激發光的能量密度，時間解析光譜將由電子-電子的能量弛緩過程，轉變為電子-聲子的能量弛緩過程，證實在PANTEC熱電元件的架構下，電子溫度與聲子溫度具有非平衡的現象。

In this dissertation, we used time-resolved femtosecond spectroscopy to study the ultrafast dynamics of Te-doped InSb with various doping electron concentration. The relaxation time of photoinduced quasiparticles was determined by fitting the relaxation process of □R/R at various ambient temperatures and with various pump fluences. According to two-temperature model, the electron-phonon coupling constant of InSb could be further estimated from the relaxation time obtained from □R/R, which strongly correlates to the number of the effective free carriers in InSb caused by optical pumping or thermal excited carriers. The electrical properties of InSb were studied by temperature-dependent Hall measurements and resistance experiments. The resistivity of heavily doped InSb represents the metal-like behavior. Surprisingly, a metal-insulator phase transition was clearly observed around 170 K in intrinsic InSb. Moreover, the shifts of plasma edges were observed by the temperature-dependent infrared reflectivity spectrum. According to Drude-Lorentz model, the plasma frequency could be obtained by fitting the infrared reflectivity spectrum. The electron effective mass, electron momentum scattering time and electron-phonon coupling constant could be calculated from the fitting parameters. The electron and phonon temperature discontinuity in the PANTEC structure was clearly observed by the time-resolved pump-probe microscope. The carrier relaxation process was changed from interband electron-electron scattering to electron-phonon scattering as increasing the pumping fluence near the interface of PANTEC structure.