Role of Carbon on the electrical, optical and structural properties of GaN

在过去的三年中，人们对碳掺杂氮化镓（GaN）的兴趣和研究表明，碳在GaN中不会作为实际的受体。独立实验得出在价带以上0.7 ~ 1 eV的深受体状态下，掺杂碳的GaN的室温p型电导率似乎是虚幻的。我们最近对分子束外延（MBE）生长的c掺杂GaN的研究支持这些方面，因为我们无法在光谱或电学上识别受体特征，例如可能用于掺杂镁的GaN。氮化镓中C形成的深度缺陷的确切微观特征仍然是很大的兴趣，因为它提供了补偿残余n型电导率的可能性。mbe生长的超纯GaN代表了一个完美的参考系统，因为它允许将该参考系统与故意引入杂质的材料进行比较。我们最近的研究结果指出了在碳掺杂GaN生长过程中结构缺陷的形成。这方面将通过参考3.0 ~ 3.4 eV能量范围内的光谱光致发光特征来进一步研究碳掺杂水平。此外，我们还认识到碳并不完全与2.2 eV左右的黄色发光带的出现有关，这将通过共掺杂含碳材料进行进一步的详细研究。提出的工作的最后一个支柱是研究AlGaN/GaN HEMT层堆叠中的碳浓度与其电性能和工作模式之间的联系。

Intense interest and research over the past 3 years in gallium nitride (GaN) doped with carbon points at the fact that carbon will not act as a practical acceptor in GaN. Independent experiments concluded on a deep acceptor state ~ 0.7 – 1 eV above the valence band and with this, room temperature p-type conductivity of carbon-doped GaN seems illusive. Our recent research on C-doped GaN grown by molecular beam epitaxy (MBE) supports these aspects, as we could not identify the acceptor character spectroscopically or electrically, as e.g. possible for the case of GaN doped with magnesium. The exact microscopic character of the deep defect formed by C in GaN remains of big interest, since it presents a possibility to compensate residual n-type conductivity. MBE-grown ultra-pure GaN represents a perfect reference system, as it allows for the comparison between this reference and material with intentionally introduced impurities. Our recent results point at the formation of structural defects during the growth of carbon-doped GaN. This aspect will be further investigated by referring spectroscopic photoluminescence signatures in the energy range between 3.0 and 3.4 eV to the carbon doping level. Further it was realized that carbon is not exclusively related to the appearance of a yellow luminescence band around 2.2 eV, which will be studied in further detail by co-doping carbon-containing material. A last pillar of the proposed work are investigations to link carbon concentrations in AlGaN/GaN HEMT layer stacks with their electrical properties and operation modes.