Study On Interface Microstructure Of InAs/GaSb Superlattice

As a promising photoelectric materials, GaSb-based materials such as GaSb/GaAs and InAs/GaSb superlattices have made great progress in the fields of infrared detector in recent years. In this dissertation, growth method, dislocation distribution, structure and electrical properties of GaSb epilayer and InAs/GaSb superlattices grown on GaAs substrates by Molecular Beam Epitaxy (MBE) were investigated systematically.The growth of highly mismatched GaSb epilayer on GaAs (001) substrates was studied both experimentally and theoretically. The two-step growth method was used and low-temperature buffer layer was introduced in order to improve the quality of the GaSb epilayer. The growth parameters of low temperature (LT) GaSb buffer layer (including growth rate, thickness, and V/III beam equivalent pressure ratio ) were studied and it was found that the optimum growth rate, thickness, and V/III beam equivalent pressure ratio of the LT GaSb buffer were 1.43μm/h, 20nm and 3.0 respectively. The LT buffer restricted the formation of the 60°misfit dislocations(MDs) during the initial GaSb epilayer growth process and then reduced the density of the threading dislocations(TD) in the epilayer.The observation of TEM shows high density dislocations in the GaSb epilayer on GaAs substrates, including the TD in the {111} glide plane and the 90°MDs at the interface of the GaSb/GaAs. GaSb epilayers grown on GaAs (001) vicinal substrate 4°misoriented towards [110] direction were studied using high resolution X-ray diffraction (HRXRD). We found that the densities of TDs in (111) plane were higher than in (111) plane and the TDs have a bigger spacing in the [110] direction than in [110] direction. This is a consequence of the unequal distribution of stress due to the miscut substrate and associated with the shape of GaSb island. The investigation of the tilt in the GaSb epilayer shows that the formation of 60°MDs is later than 90°MDs.The electrical properties of undoped GaSb/GaAs epilayer were studied by Hall measurements. The results show that the epilayers have Hall hole concentration p =3.6×10¹⁵cm^-3 and mobilityμ=4200cm²v^-1s^-1 at 77 K, which is related with the high concentration of Ga antisite defects (GaSb) in the GaSb epilayer. The experiment results show that the annealing treatment can effectively reduce the defects in the GaSb epilayer and then reduce the hole concentration, even improve the electronic mobility.High quality GaAs/GaAsSb superlattices were grown by the Sb soak using Sb/As displacement reaction on the GaAs layer surface. The effects of growth parameter of the substrate temperature, Sb flux and Sb soak time on the concentration of Sb were investigated. The results show that the Sb content in the superlattices decreased with the increasing of growth temperature due to the desorption of the Sb. The Sb4 flux and Sb4 soak time have no obvious effects on the structure of the superlattice, which means that the Sb/As exchange only happens in the surface monolayer of the GaAs.The InAs/GaSb superlattices were grown by MBE, and the influence of growth interruption and migration enhanced epitaxy (MEE) methods to the interface structure of superlattices were studied. High quality GaAs and InSb interface between InAs/GaSb superlattices were induced by the MEE technique and the Sb4-soak or As4-soak process resulted in the atom aggregation at the interface with the consequence of high interface roughness.Interface structure analysis of InAs/GaSb superlattices shows that the interface structure of InAs/GaSb superlattices has an effect on the strain in the superlattice. The InSb-type interface can increase the average lattice constant of the superlattice compared to the GaAs-type interface. Therefore, the strain can be accommodated by changing the growth parameters and controlling the interface structure.