论文标题
氮化壳（GAN）振动光谱中的碳缺陷的指纹考虑同位素效应
Fingerprints of carbon defects in vibrational spectra of gallium nitride (GaN) consider-ing the isotope effect
论文作者
论文摘要
这项工作研究了与最近报道的碳缺陷以及红外（IR）吸收和拉曼散射的新型峰值出现在碳（$^{12} c $）的浓度范围为$ 3.2*10^{17} $至$ 3.5*10^10^19} {19} cm^cm^{-3} $的浓度范围。在通过氢化物蒸气相外观（HVPE）生长的GAN样品中观察到14个独特的缺陷模式，然后与第一原理计算预测的缺陷特性进行了比较。与同位素质量效果相关的两个$^{13} c $富含样品中的振动频移表示含碳点缺陷的六个不同的配置。同位素替代的效果通过密度功能理论（DFT）计算很好地再现。特别注意最明显的缺陷，即三碳复合物（$ c_n = c = c_n $）和碳替代氮$ C_N $。 $ c_n = c = c = c_n $ dft在价值频段最大值的1.1 eV时，过渡级别（+/0）的位置（+/0）的位置（$ c_n = c = c_n $），这表明$（c_n = c = c_n）^+$提供$ {c_n}^ - $的补偿。 $ C_N = C = C_N $缺陷是突出的，但在DFT计算中具有很高的形成能。关于$ {C_N} $缺陷，显示出主机GA和N原子参与缺陷的离域振动，并显着影响同位素频移。从二元原子碳碳和碳 - 氢（C-H）配合物中发现了更多微弱的振动模式。此外，我们注意到$ c_n $，$ c_n = c = c_n $，c-h和$ c_n-c_i $缺陷的振动模式强度的变化，在IR吸收光谱中缺陷在与缺陷相关的UV/可见吸收范围内照射后。最后，证明在低于2.5 eV的缺陷吸收范围内，拉曼过程的谐振增强能够检测到碳掺杂浓度低至$ 3.2*10^{17} cm^{ - 3} $的缺陷。
This work examines the carbon defects associated with recently reported and novel peaks of infrared (IR) absorption and Raman scattering appearing in GaN crystals at carbon ($^{12}C$) doping in the range of concentrations from $3.2*10^{17}$ to $3.5*10^{19} cm^{-3}$. 14 unique vibrational modes of defects are observed in GaN samples grown by hydride vapor phase epitaxy (HVPE) and then compared with defect properties predicted from first-principles calculations. The vibrational frequency shift in two $^{13}C$ enriched samples related to the effect of the isotope mass indicates six distinct configurations of the carbon-containing point defects. The effect of the isotope replacement is well reproduced by the density functional theory (DFT) calculations. Specific attention is paid to the most pronounced defects, namely tri-carbon complexes($C_N=C=C_N$) and carbon substituting for nitrogen $C_N$. The position of the transition level (+/0) in the bandgap found for $C_N=C=C_N$ defects by DFT at 1.1 eV above the valence band maximum, suggest that $(C_N=C=C_N)^+$ provides compensation of ${C_N}^-$. $C_N=C=C_N$ defects are observed to be prominent, yet have high formation energies in DFT calculations. Regarding ${C_N}$ defects, it is shown that the host Ga and N atoms are involved in the defect's delocalized vibrations and significantly affect the isotopic frequency shift. Much more faint vibrational modes are found from di-atomic carbon-carbon and carbon-hydrogen (C-H) complexes. Also, we note changes of vibrational mode intensities of $C_N$, $C_N=C=C_N$, C-H, and $C_N-C_i$ defects in the IR absorption spectra upon irradiation in the defect-related UV/visible absorption range. Finally, it is demonstrated that the resonant enhancement of the Raman process in the range of defect absorption above 2.5 eV enables the detection of defects at carbon doping concentrations as low as $3.2*10^{17} cm^{-3}$.
