- 學位論文
溫度效應對氮化銦磊晶層光學特性的研究
Effects of temperature on the optical properties of InN epilayers
摘要
我們從吸收光譜觀察到不同載子濃度的氮化銦皆有能帶尾端的現象，這是因為有聲子做能量轉移所導致的。由變溫的螢光上升時間(Rise time)以及吸收光譜，可以推論出有一小能量的聲子存在。由變溫光激螢光光譜，觀察到隨溫度增加能量峰值有下降、上升再下降的現象，此S型行為是因為載子受到溫度的活化，脫離原本的侷域態而躍遷到高能量能態。從低溫時間鑑別光激螢光光譜與變溫的光激螢光強度可得出侷限能量與活化能，這些能量都與利用S型行為公式擬合得出的能量相互吻合。 我們利用光激螢光光譜來討論氮化銦磊晶層的載子鬆弛機制。實驗中獲得電子氣體溫度的變化，在不同的載子濃度樣品下，電子損失能量鬆弛至導帶的主要機制是以不同比例的電子-光學聲子和電子-聲學聲子交互作用的理論模型來解釋。低溫下不同載子濃度樣品的聲子生命期與理論所得的生命期有所差異，此差異可能是來自於熱聲子效應的作用。我們發現氮化銦磊晶層中，A1(LO)模態的聲子生命期隨著溫度增加而減少，表示A1(LO)模態的聲子會隨溫度以不對稱的型式衰減成一個E2(high)模式的聲子和一個小能量的聲子。
並列摘要
We observe the concentration dependence of the band-tail effect from absorption spectra of InN epilayers , due to energy transfer by phonons. Based on the temperature dependence of photoluminescence (PL) spectra, we observed an anomalous temperature dependence of the peak energy, i.e., a S-shaped (decrease-increase-decrease) peak energy as a function of temperature. This behavior is suggested to be originated from delocalization of the localized carriers by thermal activation. From the time-resolved PL and CW PL intensity from different temperatures, we obtain the localization energy and the activation energy. These energies are found to be in good agreement with the fitted energy obtained from the S-shape behavior. We studied the energy relaxation of electrons in InN epilayers using PL. It is found the measured electron temperature variation in different concentration can be explained by two different rate model based on the energy relaxation of electrons due to LO phonon and acoustics phonon scattering. Under the low temperature the different concentration sample phonon lifetime respectively is higher than the theoretical phonon lifetime. This deviation is attributed to the presence of the hot phonon effect. The A1(LO) phonon lifetime in InN decreases with increasing temperature. This tendency illustrates the A1(LO) phonon decays asymmetrically into a E2(high) and low-energy phonon.