Effect Of Reconstructures On Molecular Beam Epitaxial Growth Of GaAs

Recently, the (111)B face of GaAs has attracted increasing interest for device applications and other fundamental research due to the potential to fabricate high performance devices using properties such as a large piezoelectric effect and high light emitting efficiency. However, Molecular beam epitaxy (MBE) growth on GaAs(111)B substrates has been found to be rather difficult, because homoepitaxial growth is highly sensitive to growth parameters and the grown surfaces are easily marred by pyramid-shape structure defects.During MBE growth, the bonding atoms on uppermost surface form dimmers or trimmers to decrease the surface free energy. Various reconstructures composed of dimmers or trimmers appear on the substrate surface on different growth conditions(substrate temperature, As and Ga flux density), and the properties of epilayers grown on vaious reconstructure plateau regions are different. In this thesis, systematical research was performed to analyze the influence of growth conditions on growth process and epilayer properties. Based on the experimental results, growth conditions were optimized to decrease the size and the density of pyramid-shape structures, and growth of GaAs epilayers with specular surface, free of pyramid shape structure defects, was achieved on a nonmisoriented GaAs (111)B substrate via in situ, real time measurement of specular beam intensity of RHEED.The MBE growth of good quality GaAs epitaxy layers on (001) surface is easy to achieve, so the growth on various reconstructures plateau regions was performed to analyze the dependence of epilayers properties on growth conditions on GaAs(001) substrate. The results indicated that the morphology of epilayer surface grown on (2×4) phase(growth temperature from 450℃ to 580℃) was the best, and the roughness of epilayers grown on (2×4)-α phase, βphase, and y phase plateau regions was similar;The best crystal quality was obtained at 515 °C;The hole mobility of epilayers decreased with the increasing of Arsenic atom coverage ratio, and the epilayer grown on c(4><4) phase was n-type.Substrate cleaning is vital to the surface morphology of epilayer, and the quality of GaAs IC process such as photolithography etc. It is more difficult to define the proper etching conditions on (lll)B surface than on (001) surface of GaAs. The chemical etching experiments were performed to optimize the etching conditions.The dependence of surface morphology on growth conditions was analyzed by surface phase diagram and intensity oscillation behaviors of reflection high energy electron diffraction (RHEED) during MBE growth. The RHEED intensity of (Vl9*Vl9) phase was the highest on both static surface and dynamic growth surface, so epitaxial growth on (Vl9>Wl9) plateau region can improve the quality of epilayers surface and reduce the density and size of pyramidical structures on epilayer surface;Low Ga and As flux density can reinforce the migration of Ga atoms on growth surface, so the growth at low grown rate and low As flux density was effective to obtain epilayer with mirror-like surface;the 1000A epilayer with mirror-like surface was achieved on optimized growth conditions on nonmisoriented GaAs (lll)B substrate by normal MBE.