三族氮化物半導體光學性質研究

Abstract

本論文研究三族氮化物半導體的光學性質，研究的樣品主要包括氮化鋁(銦)鎵三(四)元磊晶薄膜、銅與矽共摻雜氮化鎵、矽摻雜氮化鎵，內容主要分為三大部分： (一)氮化鋁(銦)鎵三(四)元磊晶薄膜的光學性質： 這部分我們首先利用威廉斯-霍爾法和倒置空間對應法來計算貫穿式差排密度，並且觀察鋁含量及銦含量分別對於氮化鋁鎵以及氮化鋁銦鎵的影響。而從過去的文獻得知，氮化鋁銦鎵的量子發光效率比氮化鋁鎵來的好，但是其物理成因並不是十分清楚。首先利用光激發螢光光譜與拉曼光譜來證明似氮化銦鎵合金團的形成，更進一步的使用掃描式電子顯微鏡與原子力顯微鏡來看出一些似氮化銦鎵合金團的分佈情形，在這些量測當中，我們得到直接的證據，證明此四元化合物的高效率螢光發光是來自似氮化銦鎵合金團。 (二)銅與矽共摻雜氮化鎵的光學特性 這部分我們主要探討銅與矽共參雜氮化鎵的光學特性。利用離子佈值法，直接將高能量銅離子直入晶體中，之後在將此晶體用不同的溫度做熱退火處理。首先利用掃描式電子顯微鏡來觀察由銅離子所造成的V形缺陷，而在6K光激發螢光光譜中可得到熱退火溫度在700 OC 兩分鐘時，可將晶體恢復的最好。而在拉曼光譜中，我們發現了三個額外的峰值，並且比較在不同溫度下的離子佈植，對於晶體結構的影響，而在X光繞射實驗中，我們也發現了除了氮化鎵的峰值外，還多出一個由銅離子產生的峰值• (三)不同的矽摻雜濃度的氮化鎵 這部分主要是利用傅氏轉換紅外線光譜儀及實驗曲線回歸來分析矽摻雜濃度對於氮化鎵的影響，由此光譜可利用理論計算來得到晶體的厚度，並且比較由霍爾效應及上述方法所的到的離子濃度以及電子遷移率，在上述兩種方法中，所獲的的離子濃度成一個線性的關係，但所獲得的電子遷移率卻是觀察不出規律。而利用拉曼光譜，我們可以得到離子濃度對於氮化鎵 A1 (LO) 所造成的影響，從光激發螢光光譜，可以當離子濃度越大，會發生了能隙窄化，進而對於氮化鎵峰值造成一些紅移的現象。

This thesis concerns with the studies on the optical properties of III-Nitride semiconductors. X-ray diffraction (XRD), Photoluminescence (PL) , Raman scattering (RS), Scanning electron microscopy (SEM), Atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) are carried out to study the physical properties of III-nitride materials, including AlxGa1-xN, InxAlyGa1-x-yN, Cu-implanted GaN and Si-doped GaN. Many peculiar phenomena have been observed, which are very useful for understanding as well as application of III-nitride materials. (1)Optical properties in (In,Al)GaN We use two different X-ray analysis techniques; a Williamson Hall plot and reciprocal space mapping to obtain their threading dislocation densities for GaN, AlxGa1-xN and InxAlyGa1-x-yN epitaxial layers. A WH plot can provide information about coherence length and tilt angle from a linear fit to the line-width of the triple axis rocking curve (000l) symmetric reflections. RSM is typically used to obtain this data, but it is more involved in technique. We also report excitonic optoelectronic properties of InxAlyGa1-x-yN quaternary alloys, including PL and Raman measurements. Then, we perform scanning electron microscopy (SEM) image and atomic force microscopy (AFM) to observe the InGaN-like clusters. (2)Characterization of Cu-implanted GaN We present SEM, low temperature PL, RS and XRD in Cu-implanted GaN. Due to Cu+ ions, we can observe the V-defects from SEM image. Using PL spectrum, we calculate a value for the Cu shallow accepter energy of 200 meV. We find three additional modes in Raman spectra for Cu-implanted GaN. The implantation-induced peaks are mainly categorized into : disorder activated Raman scattering and scattering mechanisms of implantation induced defects. From XRD curves, we observed the lattice expansion in the implanted layer due to the incorporation of atoms into the interstitial sites of the host structure. Such expansion results in the compressive strain alone c axis in the neighboring un-implanted region. (3)Optical properties in Si-doped GaN We use FTIR to characterize these samples. Based on theoretical equations used to calculate the reflectance of the IR spectra, we can obtain film thickness, free carrier concentration and electron mobility of Si-doped GaN. Photoluminescence and Raman scattering have been done on GaN grown on sapphire with different Si-doping concentration. The electron concentration dependence of the band-gap energy measured by photoluminescence is interpreted as band-gap narrowing effect and evaluated by a simple relation. From Raman scattering data, we discussed the influence of the carrier concentration for Raman spectra and observed the phonon-plasmon interaction effect for the GaN A1 (LO) mode.