Reduction of the dislocation density for GaAs thin films on Si substrates grown by molecular beam epitaxy using the two-step growth method

Abstract

Rapid advancements in growth technology in recent years, such as molecular beam epitaxy (MBE) and metalorganic chemical vapour deposition, have made possible the production of several types of strained films on Si semiconductors [1-3]. Among these types of materials, GaAs/Si strained heterostructures are very attractive due to applications for electronic devices and for the investigation of fundamental physics [4-9]. Although GaAs/Si heterostructures have inherent difficulties due to the large lattice mismatch (A~/c~=4.1% at 25 °C) and the thermal expansion coefficient difference (2m/~=62% at 25 °C), they are particularly interesting because of the number of possible electronic and optical applications that result from utilizing the benefits of the high-mobility capabilities of GaAs and the wafer cost of Si. Recently, many researchers have been interested in the growth and applications of GaAs/Si heterostructures [4-9]. Although many works concerning GaAs/ Si heterostructures have been reported [4-9], there are still many unsolved problems. These problems originate from the difference between the physical properties of GaAs and Si. A typical problem is the formation of high-density defects due to dislocations induced in the GaAs epilayer. Despite many efforts to reduce the density defect, a GaAs/Si heterostructure with a low defect density has not yet been reported. More recently, Fukuda et al. reported that the high defect density in GaAs grown on Si could be reduced by a Ge buffer layer [10]. They showed that the high quality of the GaAs crystallinity was affected by the quality of the Ge buffer layer, and they suggested a two-step growth method to achieve good crystallinity in the Ge. Since the mismatches in both the thermal expansion and the lattice parameter (0.1 and 15%, respectively) between GaAs and Ge are much smaller than those (4 and 62%, respectively) between GaAs and Si, Ge acts as a good buffer layer [11]. That is,