薄膜异质结构中红外折射率的同步测量：GaAs/AlGaAs的方法与结果
Simultaneous Measurement of Mid-Infrared Refractive Indices in Thin-Film Heterostructures: Methodology and Results for GaAs/AlGaAs
AI总结：
本文提出一种结合傅里叶变换红外光谱和扫描电子显微镜的新方法，同步测量了GaAs和AlGaAs在2.0至7.1μm范围内的折射率，相对不确定度达$10^{-4}$量级，对中红外光学器件设计具有重要意义。
摘要：
我们展示了在$2.0$至$7.1\,\mathrm{μm}$（$5000$至$1400\,\mathrm{cm^{-1}}$）范围内同步测量砷化镓（GaAs）和砷化铝镓（Al$_\mathrm{x}$Ga$_\mathrm{1-x}$As）折射率的结果。这些数值取自通过分子束外延生长的高纯度单晶超晶格Bragg反射镜（背景掺杂$\leq 1 \times 10^{-14}\,\mathrm{cm^{-3}}$）。为在如此宽的波长范围内恢复折射率，我们为每种材料拟合了色散模型。通过一种成熟方法的新颖组合，我们利用傅里叶变换红外光谱法测量了Bragg反射镜的光度准确透射光谱，并利用扫描电子显微镜测量了结构的各物理层厚度。为推断折射率值的不确定度，我们估算了相关测量不确定度，并通过蒙特卡洛方法进行传播。这种高度适应性的方法最终得出，在测量的光谱范围内，GaAs和Al$_{0.929}$Ga$_{0.071}$As的传播相对不确定度均在$10^{-4}$量级。拟合模型还可以近似MBE生长的$0\leq x \leq 1$的Al$_\mathrm{x}$Ga$_\mathrm{1-x}$As的折射率。这些更新值和测量方法对于许多领域高度关注的光谱区域中下一代有源和无源光学器件的设计、制造和表征至关重要，例如中红外光谱区域的激光器设计和腔增强光谱学。
英文摘要：
We present our results for simultaneous measurement of the refractive indices of gallium arsenide (GaAs) and aluminum gallium arsenide (Al$_\mathrm{x}$Ga$_\mathrm{1-x}$As) from $2.0$ to $7.1\,\mathrm{μm}$ ($5000$ to $1400\,\mathrm{cm^{-1}}$). We obtain these values from a monocrystalline superlattice Bragg mirror of excellent purity (background doping $\leq 1 \times 10^{-14}\,\mathrm{cm^{-3}}$), grown via molecular beam epitaxy. To recover the refractive indices over such a broad wavelength range, we fit a dispersion model for each material. In a novel combination of well-established methods, we measure both a photometrically accurate transmittance spectrum of the Bragg mirror via Fourier-transform infrared spectrometry and the individual physical layer thicknesses of the structure via scanning electron microscopy. To infer the uncertainty of the refractive index values, we estimate relevant measurement uncertainties and propagate them via a Monte-Carlo method. This highly-adaptable approach conclusively yields propagated relative uncertainties on the order of $10^{-4}$ over the measured spectral range for both GaAs and Al$_{0.929}$Ga$_{0.071}$As. The fitted model can also approximate the refractive index for MBE-grown Al$_\mathrm{x}$Ga$_\mathrm{1-x}$As for $0\leq x \leq 1$. Both these updated values and the measurement approach will be essential in the design, fabrication, and characterization of next-generation active and passive optical devices in a spectral region that is of high interest in many fields, e.g., laser design and cavity-enhanced spectroscopy in the mid-infrared spectral region.
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