Du Yong, Kong Zhenzhen, Toprak Muhammet S, Wang Guilei, Miao Yuanhao, Xu Buqing, Yu Jiahan, Li Ben, Lin Hongxiao, Han Jianghao, Dong Yan, Wang Wenwu, Radamson Henry H
Key Laboratory of Microelectronic Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China.
Institute of Microelectronics, University of Chinese Academy of Sciences, Beijing 100049, China.
Nanomaterials (Basel). 2021 Apr 6;11(4):928. doi: 10.3390/nano11040928.
This work presents the growth of high-quality Ge epilayers on Si (001) substrates using a reduced pressure chemical vapor deposition (RPCVD) chamber. Based on the initial nucleation, a low temperature high temperature (LT-HT) two-step approach, we systematically investigate the nucleation time and surface topography, influence of a LT-Ge buffer layer thickness, a HT-Ge growth temperature, layer thickness, and high temperature thermal treatment on the morphological and crystalline quality of the Ge epilayers. It is also a unique study in the initial growth of Ge epitaxy; the start point of the experiments includes Stranski-Krastanov mode in which the Ge wet layer is initially formed and later the growth is developed to form nuclides. Afterwards, a two-dimensional Ge layer is formed from the coalescing of the nuclides. The evolution of the strain from the beginning stage of the growth up to the full Ge layer has been investigated. Material characterization results show that Ge epilayer with 400 nm LT-Ge buffer layer features at least the root mean square (RMS) value and it's threading dislocation density (TDD) decreases by a factor of 2. In view of the 400 nm LT-Ge buffer layer, the 1000 nm Ge epilayer with HT-Ge growth temperature of 650 °C showed the best material quality, which is conducive to the merging of the crystals into a connected structure eventually forming a continuous and two-dimensional film. After increasing the thickness of Ge layer from 900 nm to 2000 nm, Ge surface roughness decreased first and then increased slowly (the RMS value for 1400 nm Ge layer was 0.81 nm). Finally, a high-temperature annealing process was carried out and high-quality Ge layer was obtained (TDD=2.78 × 10 cm). In addition, room temperature strong photoluminescence (PL) peak intensity and narrow full width at half maximum (11 meV) spectra further confirm the high crystalline quality of the Ge layer manufactured by this optimized process. This work highlights the inducing, increasing, and relaxing of the strain in the Ge buffer and the signature of the defect formation.
这项工作展示了使用减压化学气相沉积（RPCVD）腔室在Si（001）衬底上生长高质量Ge外延层的过程。基于初始成核，采用低温-高温（LT-HT）两步法，我们系统地研究了成核时间和表面形貌、LT-Ge缓冲层厚度、HT-Ge生长温度、层厚度以及高温热处理对Ge外延层形态和晶体质量的影响。这也是一项关于Ge外延初始生长的独特研究；实验的起始点包括斯特兰斯基-克拉斯坦诺夫模式，其中最初形成Ge湿层，随后生长发展形成核。之后，由核的合并形成二维Ge层。研究了从生长开始阶段到完整Ge层的应变演变。材料表征结果表明，具有400nm LT-Ge缓冲层的Ge外延层至少具有均方根（RMS）值，其位错密度（TDD）降低了2倍。鉴于400nm LT-Ge缓冲层，HT-Ge生长温度为650°C的1000nm Ge外延层显示出最佳的材料质量，这有利于晶体合并成连接结构，最终形成连续的二维薄膜。将Ge层厚度从900nm增加到2000nm后，Ge表面粗糙度先降低，然后缓慢增加（1400nm Ge层的RMS值为0.8nm）。最后，进行了高温退火处理，获得了高质量的Ge层（TDD = 2.78×10cm）。此外，室温下强烈的光致发光（PL）峰强度和窄的半高宽（11meV）光谱进一步证实了通过这种优化工艺制造的Ge层具有高晶体质量。这项工作突出了Ge缓冲层中应变的诱导、增加和松弛以及缺陷形成的特征。
