标题： 中红外光谱椭偏和光学霍尔效应测定高铝含量Al$_x$Ga$_{1-x}$N合金的红外介电函数、声子模态和自由电荷载流子特性 显示英文标题

标题： Infrared dielectric function, phonon modes and free-charge carrier properties of high-Al-content Al$_x$Ga$_{1-x}$N alloys determined by mid-infrared spectroscopic ellipsometry and optical Hall effect

摘要： 声子模式参数和高铝含量Al$_x$Ga$_{1-x}$N合金的各向异性中红外介电函数张量分量随铝含量$x$的变化情况，通过中红外光谱椭偏测量对在4H-SiC衬底上制备的一组高质量硅掺杂Al$_x$Ga$_{1-x}$N外延层进行了精确确定。 发现$E_1$(TO) 模式表现出双模行为，而$A_1$(LO) 模式表现出单模行为，这与之前拉曼散射光谱学的报道一致。 IR活性声子频率参数的组成依赖关系被建立，并提供了关于可能由无序激活的静默$B_1$模式的讨论。 静态介电常数随$x$的变化由使用最佳匹配模型导出的声子模频率和高频介电常数参数，并应用Lydanne-Sachs-Teller关系确定。 高铝含量Al$_x$Ga$_{1-x}$N合金中的有效质量参数及其组成依赖性由中红外光学霍尔效应测量确定。 此外，具有相似硅掺杂水平的Al$_x$Ga$_{1-x}$N薄膜的自由电子浓度$N$和迁移率参数$\mu$随铝含量$x$的变化进行了研究并进行了讨论。 显示英文摘要

摘要： The phonon mode parameters and anisotropic mid-infrared dielectric function tensor components of high- Al-content Al$_x$Ga$_{1-x}$N alloys in dependence of the Al content $x$ are precisely determined from mid-infrared spectroscopic ellipsometry measurements for a set of high-quality Si-doped Al$_x$Ga$_{1-x}$N epitaxial layers on 4H-SiC substrates. Two-mode behavior of the $E_1$(TO) modes and one-mode behavior of the $A_1$(LO) mode are found in agreement with previous Raman scattering spectroscopy reports. The composition dependencies of the IR active phonon frequency parameters are established and a discussion on the silent $B_1$ mode that may be disorder activated is provided. The static dielectric constants in dependence of $x$ are determined by using the best-match model derived phonon mode frequency and high-frequency dielectric constant parameters and applying the Lydanne-Sachs-Teller relation. The effective mass parameter in high-Al-content Al$_x$Ga$_{1-x}$N alloys and its composition dependence are determined from mid-infrared optical Hall effect measurements. Furtheremore, the free electron concentration $N$ and mobility parameters $\mu$ of Al$_x$Ga$_{1-x}$N films with similar Si doping levels are investigated as function of the Al content, $x$ and discussed.