Xu Chi, Fernando Nalin S, Zollner Stefan, Kouvetakis John, Menéndez José
Department of Physics, Arizona State University, Tempe, Arizona 85287-1504, USA.
Department of Physics, New Mexico State University, Las Cruces, New Mexico 88003-8001, USA.
Phys Rev Lett. 2017 Jun 30;118(26):267402. doi: 10.1103/PhysRevLett.118.267402. Epub 2017 Jun 27.
Phase-filling singularities in the optical response function of highly doped (>10^{19} cm^{-3}) germanium are theoretically predicted and experimentally confirmed using spectroscopic ellipsometry. Contrary to direct-gap semiconductors, which display the well-known Burstein-Moss phenomenology upon doping, the critical point in the joint density of electronic states associated with the partially filled conduction band in n-Ge corresponds to the so-called E_{1} and E_{1}+Δ_{1} transitions, which are two-dimensional in character. As a result of this reduced dimensionality, there is no edge shift induced by Pauli blocking. Instead, one observes the "original" critical point (shifted only by band gap renormalization) and an additional feature associated with the level occupation discontinuity at the Fermi level. The experimental observation of this feature is made possible by the recent development of low-temperature, in situ doping techniques that allow the fabrication of highly doped films with exceptionally flat doping profiles.
理论上预测了高掺杂（>10^{19} cm^{-3}）锗的光学响应函数中的相位填充奇点，并使用光谱椭偏仪进行了实验证实。与直接带隙半导体不同，后者在掺杂时表现出众所周知的伯斯坦-莫斯现象，n型锗中与部分填充导带相关的电子态联合密度中的临界点对应于所谓的E_{1}和E_{1}+Δ_{1}跃迁，其具有二维特性。由于这种维度降低，不存在由泡利阻塞引起的边缘移动。相反，人们观察到“原始”临界点（仅因带隙重整化而移动）以及与费米能级处的能级占据不连续性相关的附加特征。最近低温原位掺杂技术的发展使得能够制造出具有异常平坦掺杂分布的高掺杂薄膜，从而使得对这一特征的实验观测成为可能。
