Germanium-on-insulator virtual substrate for InGaP epitaxy

In this work, we investigate the bonding processes to improve Germanium-on-insulator (GOI) quality for III-V integration, and an InGaP LED has been grown and characterized on this GOI substrate. The threading dislocation density (TDD) of GOI was reduced from 5.1±0.8×108 cm−2 to 4.3±0.4×107 cm−2 by chemical mechanical polishing (CMP) processes. The thermal and mechanical properties of the CMPed GOI have been characterized. It showed that a 200 nm thermal oxide layer effectively absorbed the hydrogen generated from the bonding by-product reactions, which avoided the formation of thermal bubbles and provided sufficient stability during high temperature epitaxy processes. After post-bonding annealing, a high bonding strength of 1720.6 mJ/cm2 was achieved. Then, an AlInGaP/InGaP multi-quantum well (MQW) LED was grown on GOI substrate. Compared to LED on bulk Ge substrate, LED on GOI showed high leakage current due to the presence of high TDD in the Ge layer and the LED junctions. The electroluminescence of LED on GOI was approximately 50% of the light output of LED on bulk Ge.