8,628 research outputs found
Anomalous energetics and defect-assisted diffusion of Ga in silicon
No full textWe study via first-principles calculations the energetics and diffusion of Ga in c-Si. In contrast to B and In, the favored Ga/self-interstitial complex is the tetrahedral interstitial Ga-T. Thus in the presence of self-interstitials Ga becomes interstitial, and is electrically deactivated as an acceptor. Studying the native-defect assisted diffusion, we find a self-interstitial-assisted mechanism to be favored; vacancy-assisted diffusion has a sizably larger activation energy, in agreement with the observed transient enhanced diffusion behavior. (C) 2004 American Institute of Physics
Inhibited Al diffusion and growth roughening of Ga-coated Al(100)
No full textAb initio calculations indicate that the ground state for Ga adsorption on Al(100) is on surface with local unit coverage. On Ga-coated Al(100), the bridge diffusion barrier for Al is large, but the Al --> Ga exchange barrier is zero: the ensuing incorporation of randomly deposited Al's into the Ga: overlayer realizes a percolation network, efficiently recoated by Ca atoms. Based on calculated energetics, we predict rough surface growth at all temperatures; modeling the growth by a random deposition model with partial relaxation, we find a power-law divergent roughness w similar to t(0.07+/-0.02)
Incorporation, diffusion, and electrical activity of Li in GaN
No full textFirst-principles calculations are presented for Li, a group-I candidate acceptor, in GaN. Substitutional LiGa is a double acceptor with a low first ionization energy of 0.16 eV. Its straightforward use as p dopant is hindered by Li's concurrent preference for interstitialcy, which leads to self-compensation. Interstitial Li is predicted to diffuse freely in GaN above about 600 K, and to recombine exothermically with Ga vacancies producing LiGa, both results very closely matching recent experiments on implanted Li isotopes. The effects of this interstitial-substitutional transition on the doping state of GaN are discussed, with reference to the availability of Ga vacancies in chemical incorporation of implantation, and the role of Ga interstitial donor
Influence of point defects injection on the stability of a supersaturated Ga-Si solid solution
No full textThe ultrahigh doping levels of Si needed in ultradownscaled electronic devices can be achieved forming supersaturated solid solutions by solid-phase epitaxy. These solutions are, however, unstable upon high-temperature annealing, and electrical deactivation of the impurities exceeding the solid solubility limit occurs. There are indications that deactivation is driven by the interaction of impurities with native (i.e., intrinsic) defects, but the relevant process has not been studied in detail thus far, nor have the defect complexes presumably causing the deactivation been identified. Here we use light-ion beam treatments and Rutherford backscattering analysis combined with first-principles density-functional calculations to investigate the interaction of a specific Group-III acceptor, Ga, with native defects-mostly self-interstitials-generated by irradiation at room temperature, or upon thermal annealing. Monitoring the off-lattice displacement of Ga during He-beam irradiation at room temperature or after high-temperature annealing by channeling analysis, we find a partitioning into substitutional and tetrahedral interstitial Ga populations in the former case, and a partitioning into substitutional and random populations in the latter. Based on ab initio calculations and angular-scan Rutherford backscattering spectroscopy, we are able to interpret the results in terms of (a) self-interstitial-assisted enhanced diffusion of Ga, and (b) the subsequent formation of stable Ga-Ga and Ga-Ga-Si complexes. This suggests that deactivation is indeed mediated by native defects (mainly self-interstitials) causing the off-site displacement of the Ga impurity
GA-Fuzzy PID control simulation waveform diagram.
No full textAs is well known, the metal annealing process has the characteristics of heat concentration and rapid heating. Traditional vacuum annealing furnaces use PID control method, which has problems such as high temperature fluctuation, large overshoot, and long response time during the heating and heating process. Based on this situation, some domestic scholars have adopted fuzzy PID control algorithm in the temperature control of vacuum annealing furnaces. Due to the fact that fuzzy rules are formulated through a large amount of on-site temperature data and experience summary, there is a certain degree of subjectivity, which cannot ensure that each rule is optimal. In response to this drawback, the author combined the technical parameters of vacuum annealing furnace equipment, The fuzzy PID temperature control of the vacuum annealing furnace is optimized using genetic algorithm. Through simulation and comparative analysis, it is concluded that the design of the fuzzy PID vacuum annealing furnace temperature control system based on GA optimization is superior to fuzzy PID and traditional PID control in terms of temperature accuracy, rise time, and overshoot control. Finally, it was verified through offline experiments that the fuzzy PID temperature control system based on GA optimization meets the annealing temperature requirements of metal workpieces and can be applied to the temperature control system of vacuum annealing furnaces.</div
Low In solubility and band offsets in the small- x β-Ga 2 O 3 /(Ga 1− x In x ) 2 O 3 system
No full textUsing first-principles calculations, we show that the maximum reachable concentration x in the (Ga1-xInx)(2)O-3 alloy in the low-x regime (i.e., the In solubility beta-Ga2O3) is around 10%. We then calculate the band alignment at the (100) interface between beta-Ga2O3 and (Ga1-xInx)(2)O-3 at 12%, the nearest computationally treatable concentration. The alignment is strongly strain-dependent: it is type-B staggered when the alloy is epitaxial on Ga2O3 and type-A straddling in a free-standing superlattice. Our results suggest a limited range of applicability of low-In-content GaInO alloys. (C) 2015 The Japan Society of Applied Physic
Electronic and structural properties of GaN by the full-potential linear muffin-tin orbitals method: The role of the d electrons
No full textThe structural and electronic properties of cubic GaN are studied within the local-density approximation by the full-potential linear muffin-tin orbitals method. The Ga 3d electrons are treated as band states, and no shape approximation is made to the potential and charge density. The influence of d electrons on the band structure, charge density, and bonding properties is analyzed. Due to the energy resonance of Ga 3d states with nitrogen 2s states, the cation d bands are not inert, and features unusual for a III-V compound are found in the lower part of the valence band and in the valence charge density and density of states. To clarify the influence of the d states on the cohesive properties, additional full- and frozen-overlapped-core calculations were performed for GaN, cubic ZnS, GaAs, and Si. The results show, in addition to the known importance of core-valence exchange-correlation nonlinearity, that an explicit description of closed-shell interaction has a noticeable effect on the cohesive properties of GaN. Since its band structure and cohesive properties are sensitive to a proper treatment of the cation d bands, GaN appears to be somewhat exceptional among the III-V compounds and reminiscent of II-VI materials
Ab initio shallow acceptor levels in gallium nitride
No full textImpurity levels and formation energies of acceptors in wurtzite GaN are predicted ab initio. Be_Ga is found to be the shallow (thermal ionization energy 0.06 eV); and are mid-deep acceptors (0.23 eV and 0.33 eV respectively); and are deep acceptors (0.65 eV); is a midgap trap with high formation energy; finally, contrary to recent claims, is a deep acceptor (0.65 eV). Interstitials and heteroantisites are energetically not competitive with substitutional incorporation
Supercontinent-paced magmatic destabilisation and recratonisation of the Yilgarn Craton
No full textKnowledge of the evolution of ancient cratonic lithospheres underpins our understanding of Precambrian Earth. The Yilgarn Craton has exceptionally well-preserved Archean geology, with juvenile crust formation and major orogenesis concluding in the Neoarchean, and a stabilised upper-crustal architecture developing before 2.42 Ga. However, in an apparent dichotomy, geophysical models resolve lithospheric mantle composition outside the range of xenolith data from Archean regions, indicating the lithospheric mantle has since been extensively refertilised. Post-Archean igneous and sedimentary rocks record a prolonged lithospheric evolution that is not well resolved in datasets recording bulk crustal isotopic evolution. Reconciling these, we combine interpretation of geological and geophysical data to resolve two phases of lithosphere destabilisation driven by major magmatic events at ∼2.06 Ga and at ∼1.08 Ga. During destabilisation, sub-lithospheric and sub-crustal mantle fluxes caused extensive mantle refertilisation. For 200–400 Ma post-refertilisation, distributed sedimentary basins formed during recratonisation of the now denser lithosphere. The timing of these events suggests a relationship with the early stages of supercontinent assembly: Dominant downwelling beneath the assembling supercontinent sustains a sufficiently non-tensile tectonic setting to inhibit lithospheric thinning and breakup and enhances lateral flow of any upwelling mantle. This setting allows widespread intraplate refertilisation to occur while later the assembled supercontinent provides a stable setting allowing thermal re-equilibration and recratonisation to occur. In contrast, lithospheric refertilisation during supercontinent breakup will be more susceptible to density instabilities and recycling in later collisions. Consequently, we suggest that refertilisation of extant cratonic lithosphere may dominantly have occurred during the assembly of supercontinents
Comparison between experimental and theoretical determination of the local structure of the Ga As1-y Ny dilute nitride alloy
No full textWe present a combined experimental and theoretical study of the local structure of the GaAs1−yNy dilute
nitride alloy. Experimental results obtained by x-ray absorption spectroscopy have been compared with firstprinciples
density-functional supercell calculations and with the predictions of three different valence force
field models. Both experiments and calculations find that inclusion of N induces static disorder in the Ga-As
bond length distribution. An increase of the Ga-As bond length upon N incorporation in gallium arsenide has
been observed; this is due to the competing effects of the decrease of the free lattice parameter and the tensile
strain due to pseudomorphic growth. The different theoretical calculations reproduce more or less accurately
this bond length expansion; we discuss the performance of the different valence force field models in predicting
the measured bond lengths
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