Towards low energy consumption integrated photonic circuits based on Ge/SiGe quantum wells

Abstract

Despite being an indirect bandgap material, germanium (Ge) recently appeared as a material of choice for low power consumption optical link on silicon. Thanks to a low energy difference between direct and indirect energy bandgap, optical transitions around the direct gap can be used to achieve strong electroabsorption or photodetection in a material already used in microelectronics circuits. However, many challenges have to be addressed such as the growth of germanium-rich structures on silicon or the modeling of these structures around both direct and indirect bandgaps. This paper will explore recent achievements in Ge/SiGe quantum wells structures. Quantum confined Stark effect has been studied for different quantum well designs and light polarization. Both absorption and phase variations have been characterized and will be reported. Carrier recombination processes is also an intense research topic, in order to evaluate the competition between direct and indirect band gap emission as a function of temperature. Main results and conclusion will be introduced. Finally, high performance photonic devices (modulator and photodetector) that have already been demonstrated will be presented. At the end the challenges faced by Ge/SiGe QW as a new photonic platform will be presented.

Thin and locally dislocation-free SiGe virtual substrate fabrication by lateral selective growth

“…Si pillar seems to be pinned with the BOX and the SiO 2 cap during the cooling because of lower thermal energy, resulting in tensile strain formation. In the μ-Raman spectrum measured at ∼1 μm away from the Si pillar toward [1][2][3][4][5][6][7][8][9][10] direction [Shown as a red rectangle in Fig. 1(a)], the Si-Si peak at 516.0 cm −1 assigned to the Si pillar has disappeared.…”

“…The tensile strain is caused by the difference in thermal expansion between Si and SiGe and by the partial compressive strain of SiGe in lateral direction. The degree of the strain is slightly higher at the corner of the SiGe because the diagonal area is pulled by both [1][2][3][4][5][6][7][8][9][10] and [−1-10] directions. The Ge incorporation is increased by the tensile strain.…”

“…Virtual substrates (VS) of group IV materials such as SiGe and Ge are essential for fabricating high-performance and emerging devices. [1][2][3][4][5] However, because the SiGe VS is fabricated by heteroepitaxy on a Si substrate, strain is formed at the interface. Therefore, surface roughening and crystalline defect formation, which are caused by the strain fluctuation, cannot be avoided.…”

“…[17][18][19][20][21] By depositing heteroepitaxial material in a high aspect-ratio window, whose height/width ratio is typically higher than ∼1. 4, the TDs can be trapped at sidewalls because the TDs are grown on (111) plane. After trapping the TDs, the upper part of the selectively grown SiGe and Ge layers become theoretically dislocation-free.…”