Enhancements of direct band radiative recombination from Ge

High performance light emitters on silicon are one of the most urgent components for silicon-based Electronic-Photonic Integration Circuits (EPICs). Many efforts have been devoted to create the lasing condition in Si such as Si nanocrystals, Er-doped Si, SiGeSn alloy, Si/SiGe cascade structure. However, the avaliable laser emission in Si is not reported yet. The difficulty of lasing emission in pure Si arises from the fact of the indirect band gap nature of Si; the electron and hole pair recombination needs phonon assistance for momentum conservation between conduction band and valance band. The second-order recombination process makes the low stimulated emission rate and degrades the light efficiency in bulk-Si.



Germanium (Ge) is expected to be the possible candidate for silicon-based EPICs due to its high carrier mobility, strong photon absorption, pseudo-direct band gap, 1.55um light emission and high Si compatibility. Similar to silicon, Ge is an indirect band gap material. However, the small energy difference between direct and indirect valley (~136meV) makes the direct radiative transition in Ge easier than in Si. We have demonstrated several methods to enhance direct radiative transition in Ge, such high doping concentration, the elevated temperature, high pumping excitation, mechanical strain and epitaxial strain from thermal expansion. The direct radiative transition is the key issue that determines the optical gain in Ge laser devices.


 Related Publications:
  1. T. -H. Cheng, K. -L. Peng, C. -Y. Ko, C. -Y. Chen, H. -S. Lan, Y. -R. Wu, C. W. Liu, and H. -H. Tseng, “Strain-enhanced photoluminescence from Ge direct transition,” Appl. Phys. Lett., Vol. 96, 211108, 2010.
  2. T. -H. Cheng, C. -Y. Ko, C. -Y. Chen, K. -L. Peng, G. -L. Luo, C. W. Liu, and H. -H. Tseng, “Competitiveness between direct and indirect radiative transitions of Ge,” Appl. Phys. Lett., Vol. 96, 091105, 2010.