Investigations On The Properties Of Ⅲ-Ⅴ Nitrogen And/or Boron Incoporated Compounds And GaAs Nanowires

The research work of this doctoral thesis is mainly supported by such projecets as listed below. Project One "Theory on heterogeneous materials compatibility and key structure&technology innovations for monolithic integrated optoelectronic devices "(Project No.2003CB314901), which belongs to the Major State Basic Research Development Program (973Program)(Project No.2003CB314900) that Professor Ren Xiaomin is responsible for as a chief scientist. Project Two "The exploration of novel materials and special superlattice structures for heterogeneous semiconductor compatibility"(Project No.2010CB327602), which belongs to Major State Basic Research Development Program (973Program)(Project No.2010CB327600) in Professor Ren Xiaomin’s charge; National High-tech Research and Development Program of China (863Program)"The innovative researches of Ⅲ-Ⅴ optoelectronic materials with boron incorporated for monolithic integrated’,(Project No.2009AA03Z417), and the "111" Program of China (No.B07005).This work is mainly focused on the novel optoelectronic semiconductor compounds containing nitrogen and/or boron for monolithic integration, and the properties of GaAs surface and nanowires. The research results, as listed below, have been achieved.1. Investigations of ternary semiconductor compounds with nitrogen incorporated.Using first-principles total energy calculations, we have studied the structural and electronic properties of GaNxAs1-x, GaNxP1-x, GaAsxP1-x alloys within density-functional theory (DFT) framework. The validity of local density approximation (LDA) and generalized gradient approximation (GGA) has been demonstrated by the calculations of lattice parameters and band-gap bowing. The lattice constants of GaNAs and GaNP are in line with Vegard’s law, and the band-gap bowing parameters are relatively large. The relaxation effects of atoms and bonds have also been discussed. The relaxation contributes significantly to band-gap bowing. The influence of nitrogen atoms arrangements to band-gap of GaNP has been investigated, which indicate that N clusters decrease the band gap.2. Investigations of quaternary semiconductor compound GaNAsPAccording the band-gap bowing parameters of ternary alloys, we have depicted the band-gap evolution of quaternary GaNAsP alloy matched to Si. Furthermore, we overcome the difficulty of model-selection for quaternary alloys by Special Quasirandom Structures models (SQS), and calculate directly the structural, electronic and optical properties of GaNAsP matched to Si.3. Investigations of GaAs doping with Boron and Nitrogen.The electronic and structural properties of ternary alloys BGaAs, BNAs and BGaN have been calculated within DFT framework. The lattice constants of BGaAs and BGaN are in line with Vegard’s law, but that of BNAs show a deviation to Vegard’s Law. We have calculated the band-gap evolution curve of BGaNAs matched to Si by the band gap bowing parameters of relevant ternary alloys, and also get the electronic and structural properties by SQS method. The influence of distribution and arrangements of Boron and Nitrogen atoms has been analyzed; the configurations with uniform distribution of Boron and Nitrogen have relatively lower energy and higher stability.4. Investigations of III-V quaternary compounds with Boron incorporated.We also calculated the properties of quaternary compounds BGaInAs, BInPSb and BInAsP by first principles calculations on their SQS models. The results show that BGaInAs within the range B<30%matched to GaAs lattice is a direct band-gap material, whose band gap is0.45eV～1.516eV. The band-gap range of BInPSb and BInAsP matched to Si or GaAs has also been obtained.5. Single crystal zinc-blende BGaAs epilayers and ten periods of BGaAs/GaAs MQW have been successfully grown on GaAs (001) substrates by MOCVD. We have analyzed the influence of temperature and mole proportion on the ratio of B incorporation. The optimal growth temperature for BGaAs is580℃,and the maximum boron composition is up to5.5%. XRD test demonstrate that the quality of BGaAs epilayer is high. Furthermore, BGaInAs alloy matched to GaAs and BGaInAs/GaAs MQW have been grown on GaAs substrate successfully. XRD results show that both of them have high quality.6. We have investigated surface reconstruction of zincblende GaAs (112)A and GaAs(112)B surface using first-principles calculations. Ga-Ga and As-As dimmers are formed on GaAs (112)A and GaAs(112)B surface respectively. The results show that the surface free energy of relaxed GaAs (112)A is relatively lower. The surface relaxation mainly comes from the top two layers. The analysis of surface electronic properties also has been demonstrated. Surface reconstructions of wurtzite GaAs (1010)A and GaAs(1010)B surfaces have been investigated. The results show that Ga-Ga and As-As dimmers are formed on GaAs (1010)B surface while there are no reconstructions formed on GaAs (1010)A. The relaxed GaAs WZ(1010)A surface has lower surface free energy and higher stability.7. We have constructed six different types of GaAs nanowires with different diameters along GaAs(111) direction. The dangling bond densities of these structures with different diameter have been calculated. Results show that WZ2type has the lowest density of dangling bond. With the diameters increase, the sidewall of ZB type nanowires approach to ideal bulk surface more quickly than WZ type. The average cohesive energies of these nanowires with different diameters have been calculated by first-principles. We found that the cohesive energy increase with diameter, and cohesive energy of WZ type is higher than that of ZB type in the range of smaller diameter, while it becomes to be opposite in the range of lager diameter.