【作者】 张李骊；

【导师】 郑有炓； 陈敦军；

【作者基本信息】 南京大学 ， 微电子学与固体电子学， 2013， 博士

【摘要】 Ⅲ族氮化物半导体材料中的AlN、GaN、InN以及它们的三元或者四元合金化合物均为直接带隙材料,并且可以通过调节组分使其合金化合物的带隙从红外到紫外波段内连续变化。布拉格反射镜(DBR)是微腔器件重要的组成部分,可见和近紫外区的AlGaN/GaN DBR或AlInN/GaN DBR已得到广泛研究,而应用于紫外区的AlGaN/Al(Ga)N或AlInN/Al(Ga)N DBR,由于高A1组分的AlGaN生长比较困难,再加上为了避免高反射区内的光吸收,DBR结构需同时采用两种高A1组分的AlGaN合金材料,限制了折射率的差值,使其研究较晚且进展不大。本论文基于Brunner等人的经验公式模拟了高Al组分AlGaN折射率的变化规律,并依此设计了高反区在日盲波段的AlGaN/AlInN DBR结构,采用分子束外延方法制备了两种AlGaN/AlInN DBR结构。同时,利用X射线衍射(XRD)、紫外-可见光分光光度计、透射电镜(TEM)、二次离子质谱仪(SIMS)等测试设备表征了DBR的微结构和光学特性,对DBR结构的应变以及光学特性做了深入的分析研究。取得的主要研究结果如下：1、利用薄膜光学中的传输矩阵法,计算了构建在LT-AlN缓冲层上的Al0.98In0.02N/AlyGa1-yN DBR结构在中心波长为246nm处的峰值反射率随Al组分的变化规律。在波长246nm处,AlyGa1-yN的折射率随A1组分的增加而降低,从而降低了DBR两种材料的折射率差,进而导致DBR的中心反射率也随着AlyGa1-yN中A1组分的增加而降低。2、采用MBE方法制备了不同周期和A1组分的AlxIn1-xN/AlyGa1-yN DBR结构,DBR结构的第一层和最后一层均为高折射率材料(AlGaN)。通过(0002)对称面和(105)非对称面XRD衍射谱以及倒易空间图计算分析得到了不同DBR结构的应变状态,结果显示在AlInN/AlyGa1-yN DBR结构中,AlGaN层的Al组分越高,周期数越多,DBR外延膜所累积的应变越大。此外,基于XRD模拟分析和SIMS测试结果,得到了DBR双层结构中合金的元素组分比。3、所制备的Al0.98In0.02N/Al0.8Ga0.2N DBR在高反射区的中心波长在246nm,其峰值反射率为83.9%、高反射区半高宽为18nm。根据实验结果分析得到该结构在246nm处的折射率差为9.25%,相比中心波长在近紫外波段的GaN基DBR,该结构呈现出一个相对较高的折射率差值。基于实验测试的DBR参数,采用传输矩阵法模拟了该结构的反射谱,发现实验所测得的反射谱与模拟结果存在较大偏差,分析认为在DBR的TEM图像中所观察到的AlInN和AlGaN非均匀层厚和不平整的AlInN/AlGaN界面是造成这个偏差的主要原因。4、依据实验结果所提取的折射率模拟了中心波长在246nm的日盲紫外Al0.98In0.02N/Al0.8Ga0.2N DBR结构,要使DBR在高反区反射率高于99%所需要的最少周期数为25.5对,模拟得到该结构的高反射区半高宽为19nm。更多还原

【Abstract】 Ⅲ-nitride materials (AIN, GaN, InN and their ternary or quaternary alloy compounds) are direct-band gap semiconductors. Owing to their advantages of the band gaps from0.7eV to6.2eV by adjusting the component and excellent physical and chemical stabilities, Ⅲ-nitride semiconductors are the most favorite material system for the fabrication optoelectronic devices operable from infrared to ultraviolet spectrum region. Distributed Bragg reflectors (DBRs) based on AlGaN/GaN or AlInN/GaN have been carried out in microcavity devices, which work in visible and near-ultraviolet region. However, the research on DBRs structure used in the ultraviolet region stem from the difficulty for growth good qulity high-A1-content AlGaN and the big strain in the structure caused by the lattice mismatch and thermal mismatch.In this dissertation, the regularity of the refraction index of the high-Al content AlGaN and AlInN is simulated by the formula provided by Brunner. And two solar-blind AlGaN/AlInN DBRs structures are designed and fabricated on an AIN template by plasma-assisted molecular-beam epitaxy. The properties of the two DBRs are also investigated by experimental characterizations. The main conclusions we have obtained are listed as follows: 1. The peak reflectivity variation of Al0.98In0.02N/AlyGa1-yN DBR structure with central wavelength at246nm fabricated on LT-AIN layer is calculated by the transfer matrix method. The refractive index values of AlyGa1-yN at246nm decrease as the Al content increasing, which results in reduction the refractive index difference between two layers in DBRs. And this lead to decrease the peak reflectivity of DBRs with increasing Al component in AlyGa1-yN layer.2. Two solar-blind AlGaN/AlInN DBRs structures with different periods and Al concentration are successfully grown by MBE. The strains in the DBR samples are analyzed by high resolution x-ray diffraction (HRXRD) and reciprocal space mapping (RSM). The results show that the strains in the samples increase with the Al composition and the DBRs period increasing. And the contents of In, Al and Ga in the two DBR structures are measured by SIMS and simulated by HRXRD.3. The13.5-pair Al0.98In0.02N/Al0.77Ga0.23N DBR structure exhibited a peak reflectivity of83.9%with central wavelength at246nm and a stopband width of18nm. The average refractive index contrast extracted from experimental data was9.25%for the Al0.98In0.02N/Al0.77Ga0.23N DBR at246nm, which is unexpectedly high. Based on the experimental refractive indices, the reflectivity spectrum of the DBR structure is simulated using the transfer matrix method. The results show that there some discrepancy exists between the simulated and experimental reflectivity spectra. Our investigations indicate that the the discrepancy is ascribed to the nonuniformity of layer thickness and the blurry, rough interface between the AlInN and AlGaN layers.4. Simulation results based on the experimental data indicated that a25.5-period Al0.98In0.02N/Al0.8Ga0.2N DBR will exhibit reflectivity higher than99%and a stopband width of19nm centered in the solar-blind UV region.更多还原