With the rapid development of optical communication and interconnect, electronic photonic integrated circuits (EPICs) play a more and more important role in data transfer. Silicon photonics is now considered as the most promising platform for the integration of electronic and photonic devices owing to the compatibility with mature complementary metal-oxide-semiconductor (CMOS) technology. However, the development of compact and efficient active components is still challenging. SiGe material system is an appealing solution to achieve CMOS compatible active components with competitive advantages in aspects of low working voltage, high speed operation and low power consumption. Although silicon and germanium are both indirect gap semiconductors, germanium has a useful direct Γ-valley band gap only 136 meV higher than the indirect L-valley band gap.
In this paper, a novel asymmetric Ge/SiGe CQW structure is proposed and analyzed theoretically. By designing two different width quantum wells for the CQW, we can tailor the electro-optical properties of the CQW through controlling the degree of the coupling between the wave functions. An 8-band kŸp model is employed to calculate the eigenstates and absorption spectra of the CQWs. The simulation results show unique physical characteristics which strongly differ from the standard uncoupled QW. And the modulation performance is far better than the symmetric CQW previously demonstrated.We can achieve an electro-refractive index variation as high as 9×10-3at the wavelength of about 1461 nm under the electric field of 30 kV/cm. The product VπLπof half-wave voltage and length of phase shift region is estimated to be 0.01 V cm. The proposed asymmetric Ge/SiGe CQW scheme provides a promising candidate for high speed, low voltage, low power consumption and compact optical phase modulators in silicon-based integrated optoelectronic devices.
The paper is published on Optical Express (Vol. 25, Issue24, 2017.doi: 10.1364/OE.25.030032). This work is supported by the National Natural Science Foundation of China under Grant No. 61435004.
Fig.1. Electro-refractive index variation of the CQWs under different electric field operation for: (a) TE polarization, (b) TM polarization.
