To obtain high quality GaAs thin films grown epitaxially on silicon, several major challenges must be overcome. First, a very high density of dislocations are usually introduced at the interface stemming from the high lattice mismatch (4% for Si), which induces stress and cracking problems. These problems are further enhanced by the large mismatch in the thermal expansion coefficients between Si and GaAs. Furthermore, as Si is a nonpolar semiconductor and GaAs is a polar semiconductor, the growth of GaAs on Si leads to high density antiphase domain formations.
This project concentrates primarily on the epitaxial growth and characterization of compound semiconductors, such as GaAs, on silicon substrates. The objective of this project is to successfully realize highquality single-crystalline III-As epifilms on silicon, yielding highperformance and cost-effective light sources, such as light emitting diodes (LEDs), lasers, operating in the range of the important telecommunication wavelengths.
To overcome these problems, we have developed a patterned growth scheme where InGaAs/GaAs quantum wells (QWs) will be deposited on Si substrates with SiO2 masks by the Frank-van-der-Merwe (FM) mechanism. Thus, the defect densities due to finite strain energy and anti-phase domain disorders will be reduced, thereby improving optical properties. In such a way, integrating the high quality InGaAs/GaAs quantum well double-heterostructure with Si will become plausible, yielding InGaAs/GaAs lasers operating in the range of the important telecommunication wavelengths of 1.3 μm and 1.55 μm on Si. So far, we have successfully demonstrated high-quality, defect-free and atomicallysmooth GaAs thin films as well as InGaAs/GaAs double heterostructures on silicon using a record-thin buffer layer.
Another way of overcoming the challenges relating to heteroepitaxial growth mentioned earlier is to employ van der Waals epitaxy for the deposition of GaAs on silicon using a two-dimensional layered material, graphene as a lattice mismatch/thermal expansion coefficient mismatch relieving buffer layer. Through an optimized growth technique, we have recently demonstrated an atomically smooth lowtemperature GaAs nucleation layer which presents the first example of an ultrasmooth morphology for GaAs films on silicon using quasi van der Waals epitaxy, making it a remarkable step towards an eventual demonstration of the epitaxial growth of GaAs for heterogeneous integration.
High-quality and defect-free GaAs were successfully grown via molecular beam epitaxy on silicon dioxide patterned Si (111) substrates by a two-step growth technique. Compared with the one-step approach, the two-step growth technique has been found to be a better pathway to obtain single-crystalline GaAs with a remarkably lower defect density on silicon.