Fabrication of crack-free strained SiGe/Ge multiple quantum wells on Ge-on-Si(111) by the patterning method

We fabricate strained SiGe/Ge multiple quantum well (MQW) structures on Ge-on-Si(111). It is clearly found that high -density crystal cracks are generated in the MQW due to the accumulated tensile strain when the total thickness of the MQW increases beyond the critical thickness. In this study, we determine the critical thickness of the strained SiGe/Ge (111) MQW. Moreover, we demonstrate the mesa -patterning of the Ge-on-Si prior to the MQW growth can drastically suppress the crack formation, leading to the significant increase in the critical thickness. As a result, we find that room -temperature photoluminescence from the crack -suppressed MQW is highly enhanced. This indicates that the suppression of crack formation by the patterning method is very promising toward SiGe/Ge MQW embedded lightemitting device applications.