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

在过去的三年里，人们对掺碳氮化镓(GaN)的浓厚兴趣和研究表明，碳在GaN中并不是一个实际的受主。在价带上方~0.7-1 eV的深受主态上进行的独立实验表明，碳掺杂GaN的室温p型电导似乎是虚幻的。我们最近对分子束外延(MBE)生长的C掺杂GaN的研究支持了这些方面，因为我们无法通过光谱或电学来识别受主特性，例如对于掺镁的GaN。碳在GaN中形成的深缺陷的精确微观特征仍然是人们非常感兴趣的，因为它提供了补偿剩余n型电导的可能性。分子束外延生长的超纯GaN代表了一个完美的参比系统，因为它允许在这个参比与故意引入杂质的材料之间进行比较。我们的最新结果指出，在碳掺杂GaN的生长过程中会形成结构缺陷。这方面将通过参考在3.0和3.4 eV之间的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，人们还意识到碳并不完全与2.2 eV附近黄色发光带的出现有关，这将通过共掺杂含碳材料进行更详细的研究。拟议工作的最后一个支柱是研究AlGaN/GaN HEMT层叠中的碳浓度与其电学性质和操作模式之间的联系。

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.