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arXiv 2003.00143cond-mat.mtrl-sci
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Ge的变温光致发光:实验与理论

Temperature-dependent photoluminescence in Ge: experiment and theory

José Menéndez, Christian D. Poweleit, Sean E. Tilton

摘要:

我们报告了在12 K温度下对高质量Ge样品的光致发光研究$\leq$ T $\leq$ 295 K,光谱范围涵盖间接能隙的声子辅助发射(在布里渊区的L点处的最低导带和$Γ$点处的价带顶部之间),以及直接带隙发射(从导带在$Γ$点的局部最小值)。光谱显示出丰富的结构,具有作为T的函数的快速变化的线形。一个理论来解释实验结果使用解析表达式的贡献LA,TO,LO和TA声子。精确地在$Γ$和L点处的状态耦合对于后两种声子模式是被对称性禁止的,但是对于附近的状态是允许的,并且可以使用波矢相关的变形势来解释。预测和观察到的光致发光线形之间获得了很好的协议。的预测信号的分解在不同的声子的贡献意味着,近室温的间接光吸收和发射主要由禁止的过程,和允许的过程的变形潜力小于先前假设的。

英文摘要:

We report a photoluminescence study of high-quality Ge samples at temperatures 12 K $\leq$ T $\leq$ 295 K, over a spectral range that covers phonon-assisted emission from the indirect gap (between the lowest conduction band at the L point of the Brillouin zone and the top of the valence band at the $Γ$ point), as well as direct gap emission (from the local minimum of the conduction band at the $Γ$ point). The spectra display a rich structure with a rapidly changing lineshape as a function of T. A theory is developed to account for the experimental results using analytical expressions for the contributions from LA, TO, LO, and TA phonons. Coupling of states exactly at the $Γ$ and L points is forbidden by symmetry for the latter two phonon modes, but becomes allowed for nearby states and can be accounted for using wave-vector dependent deformation potentials. Excellent agreement is obtained between predicted and observed photoluminescence lineshapes. A decomposition of the predicted signal in terms of the different phonon contributions implies that near room temperature indirect optical absorption and emission are dominated by forbidden processes, and the deformation potentials for allowed processes are smaller than previously assumed.

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