Form GaAs/IngaAs Lasers on Virtual Ge

Abstract

Reliable GaAs-based optoelectronic devices, such as GaAs/InGaAs quantum well lasers, can be realized on silicon substrates using several advanced techniques. Fabrication involves first forming germanium (Ge) stripes on a silicon dioxide (SiO₂) trench-patterned silicon substrate via aspect ratio trapping (ART), where any defects originating from the Ge/Si interface are trapped by laterally confining sidewalls. Defects arising from above the SiO2 film are reduced by means of an optimized epitaxial lateral overgrowth (ELO) process followed by chemical mechanical polishing (CMP) to provide a planar Ge surface. Then, a GaAs/InGaAs laser structure is overgrown on the virtual Ge substrate. This new fabrication method overcomes traditional problems plaguing GaAs/Ge integration, including Ge autodoping and antiphase domain defects in GaAs.

In recent decades, much effort has been made to fabricate electronic and optical devices on GaAs/Si.^1-6 However, major problems remain unresolved, in particular, the high density of threading dislocations in GaAs layers grown directly on Si due to the 4-percent lattice mismatch and the difference in the coefficient of thermal expansion (CTE) between the two materials. The threading dislocations act as nonradiative recombination centers in optical devices and lead to device performance degradation. To date, significant progress has been made in reducing GaAs dislocation density for material growth by employing various epitaxial schemes such as cycle thermal annealing,⁴ epitaxial lateral overgrowth,⁵ and growth on compositionally graded SiGe buffers.⁶ However, these methods generally require relatively thick epitaxial layers and/or high-temperature annealing steps, which may complicate integration with Si-based integrated circuit technologies.