We systematically characterized the inhomogeneous doping properties along the c-axis of Mg-doped p-GaN microrods. Axial variation of doping concentration and electrical resistance on the p-GaN rod were measured by time-of-flight secondary-ion-mass-spectrometry and four-point probe measurements, respectively. Defects-related optical information was obtained from photoluminescence spectra together with Raman experiments revealing the change of crystal quality and strain along the rod. On the basis of a correlation of these analyses, we confirmed that Mg concentration decreased along the axial direction of the rod, leading to increasing electrical resistance. This axial Mg concentration change was revealed by green luminescence because the intensity of green luminescence sensitively varied with the doping density in both high-doping and low-doping rods. Interestingly, all the resistances at the highly doped rods were higher than the lowly doped rods due to overall mobility degradation at the high-doping rods caused by a scattering effect of increased Mg impurities and strain. All analyses provided complementary information on the p-type doping process and contribute to understanding the p-doping properties of GaN rod based photonic devices. Furthermore, our axially resolved optical spectroscopic (photoluminescence and Raman) methods can provide a facile, fast, and nondestructive way to estimate the axial doping and conductivity inhomogeneity of a Mg-doped p-GaN rod without having complex, time-consuming, and destructive structural and electrical measurements.

中文翻译：

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掺杂Mg的GaN棒的轴向不均匀性：成分分析，电分析和光学分析之间的强相关性

我们系统地表征了掺杂Mg的p -GaN微棒沿c轴的不均匀掺杂特性。p上掺杂浓度和电阻的轴向变化-GaN棒分别通过飞行时间二次离子质谱法和四点探针法测量。缺陷相关的光学信息是从光致发光光谱以及拉曼实验中获得的，揭示了沿棒的晶体质量和应变的变化。基于这些分析的相关性，我们确认了镁浓度沿棒的轴向降低，导致电阻增加。由于绿色发光的强度随高掺杂和低掺杂棒中的掺杂密度敏感地变化，所以轴向Mg浓度变化由绿色发光揭示。有趣的是，由于增加的Mg杂质和应变的散射效应导致高掺杂棒的整体迁移率下降，因此高掺杂棒的所有电阻都高于低掺杂棒。所有分析都提供了有关以下方面的补充信息：p型掺杂过程有助于理解基于GaN棒的光子器件的p掺杂特性。此外，我们的轴向分辨光谱法（光致发光和拉曼光谱法）可以提供一种简便，快速且无损的方法来估算掺Mg的p -GaN棒的轴向掺杂和电导率不均匀性，而不会造成复杂，费时和破坏性结构和电气测量。