The Growth And Characterization Of High Lattice-mismatched InGaAs Heterostructure By MOCVD

In GaAs is an important material for the near-infrared detection of 1-3 ?m.Due to the absence of a homogeneous substrate,the lattice-mismatch occurs during the growth of In_xGa_1-xAs?x>0.53?and brings a deteriorating effect to the crystalline quality of the epilayer if we don't take effective measures.Lattice-mismatch has always been a major problem to be solved in the heteroepitaxy of semiconductor materials.Buffer layer was invented to solve the epilayer deterioration caused by the lattice-mismatch.It has been proved to be an effective method for the misfit strain relaxation in hererostructures.By the use of buffer layer,the epilayer with superior crystalline quality was obtained.Although the buffer layer has been studied for a long time,there is still no complete mechanism or model of the buffer layer was proposed.The lack of the buffer theories makes it impossible for us to optimize or design the buffer layer structure,and deal with the heteroepitaxy properly.In this thesis,the two-step growth technique,in which a preceding low-temperature buffer?LT-buffer?layer is deposited before a high-temperature film growth,has been introduced to solve the lattice-mismatch.An In₀.78Ga₀.22 As epilayer with superior crystalline quality was successfully grown on GaAs substrate when the lattice-mismatch is 5.6%.The LT-buffer and the interfacial dislocations were studied,and the following are the main research results:1.In₀.78Ga₀.22 As epilayers were grown on the GaAs substrate by MOCVD.The experimental results show that the LT-buffer solves the lattice mismatch effectively,and the misfit strain relaxation differs a lot when the buffer thickness is different.The LT-buffer layer with an appropriate thickness can lead an effective strain relaxation,resulting in a superior crystalline quality of epilayer.In addition,the LT-buffer can suppress and reduce the dislocation density.Kinds of the studies and characterizations show that the LT-buffer layer with an appropriate thickness is the key for the misfit strain relaxation,and an essential foundation to slove the lattice mismatch.2.In₀.78Ga₀.22As/GaAs mismatched heterostructures were studied and analyzed by HRTEM.The relationship between the interfacial dislocations and misfit strain relaxation was analyzed,the mechanism of dislocation density reduction by LT-buffer was also investigated experimentally:Different misfit strain relaxation was attributed to the type and arrangement of interfacial dislocations.Highly periodic 90° dislocation array was responsible for the most effective strain relaxation.The coalescence and burial between islands in the LT-buffer directly determine the misfit strain relaxation in different growth stage,different arrangement of dislocations will leads to changes in strain relaxation.The analysis and studies above provide us the optimization and control direction of the LT-buffer,so as to achieve the regulation of strain relaxation in heterostructures,and obtain the InGaAs epilayers with superior crystalline quality.3.XPS and UPS were employed to investigate the band structure of In₀.82Ga₀.18As/InP with a 1.9% lattice-mismatch.The valence band offset was determined to be 0.413 eV,and the conduction band offset is 0.457 eV based on the energy gap values of In₀.82Ga₀.18 As and InP.The accuracy of the band offset determination was verified by experimental and theoretical calculations.Finally,the In₀.82Ga₀.18As/InP heterostructure shows a type-I straddling band structure.The determination of In₀.82Ga₀.18 As /InP heterostructure is of great significance.The energy band regulation offers us the possibility of controlling the process of carrier transport,and lay the foundation for the diversification and innovation of the heterostructure device.