Research On Superlattice Epitaxy And Surface Structure Of Antimonide Based Semiconductors

The Sb-based III-V semiconductor compounds and their heterostructures such as superlattices (SL) and quantum wells have attracted much attention for their applications in infrared detection recently. The material isssues such as poor surface diffusion and As/Sb exchange limit improvements of the antimonide heterostructures. The main topic in this dissertation is the study of antimonide surface reconstructions and the effects on the surface morphology, 60°dislocation formation, and Sb-for-As exchange in epitaxy. The other topic in this thesis is the design and fabrication of barrier infrared detector based on InAs/GaSb SL. The main research and achievments are as follows:Homoepitaxial and heteroepitaxial GaSb films were grown by molecular beam epitaxy (MBE). Atomic force microscopy (AFM) shows that all the GaSb films present mound morphology with elongation along [ 110] direction. The dislocation density, tilt and coherent length resulting from dislocation, and relaxation degree along <110> directions were characterized by high-resolution X-ray diffraction (HRXRD). The mesurements demonstrate that the AlSb buffer layer can increase relaxation degree of GaSb heteroepitaxial film along [ 110] direction with deduction of density of threading dislocation.The adsorption and diffusion properties of a Ga adatom deposited on GaSb(001)-α/β(4×3) were investigated by first-principles calculations. Combining with the experimental data, the calculation results have been utilized to interpret the morphology anisotropy of GaSb films: the distribution and depth of adsorption sites and saddle points are determined by the type and arrangement of the surface dimer row, and [ 110] is fast diffusion direction of Ga adatoms on the GaSb(001)-(4×3) surface. Besides, the study of bravais lattice diversity reveal that, the 60°misfit dislocations nucleation through shift of 90°dislocation array on the AlSb(001)-c(4×4) surface could be suppressed owing to the high symmetry of the reconstruction.HRXRD and high-resolution transmission electron microscopy (HRTEM) were performed to estimate the GaSb component of GaAs/GaAsSb SL which grown by Sb soak method. Luminescence from GaAsSb well and Sb-rich regions were observed and the Sb surface incorporation in the SL growth were analyzed thermodynamically. Furthermore, Sb-for-As exchange at the GaSb covered GaAs (GaSb/GaAs) surface was investigated using first principle calculations. Sb substitution for subsurface As atoms with weak Ga–As bonding arrangements are energetically favored at the strained GaSb/GaAs surface. After the Sb-for-As exchange, the formed GaSb layer can be stabilized against degradation from As-for-Sb exchange in the growth of GaAs/GaAsSb SL.Band structure of GaSb, AlSb and InAs/GaSb SL were calculated by empirical tight-binding method (ETBM) within the frame of sp3s* base sets and first-nearest-neighbor approximation. The effects of thickness, interface structure and surface segregation on band structure were analyzed. The band structure of InAs/GaSb SL modified by Al(Ga)Sb layers (M-SL) was investigated by tight-binding parameters of AlSb at 77K, which fitted to the reported band data.We grown the InAs/GaSb SLs with different interface type by MBE, interface structure of SLs was characterized by Raman scattering and cross-sectional HRTEM. The barrier infrared detector consisting of InAs/GaSb SL was design and fabricated. At 90K, a 5μm 50% cutoff detector exhibits a dark current 50mA/cm² with -0.5V bias, and a blackbody detectivity of 2.8×10⁹cm·Hz^1/2/W with zero bias.