A comprehensive thermodynamic analysis of native point defect and dopant solubilities in gallium arsenide

Abstract

A detailed analysis of the role of charged native point defects in controlling the solubility of electrically active dopants in gallium arsenide is presented. The key roles of (a) positively charged arsenic vacancies (VAs+) in determining the doping range over which the solubility curve is linear and (b) multiply negative charged gallium vacancies (VGam−) determining annealing and diffusion behavior in n+ material are demonstrated. An equilibrium thermodynamic model based on these concepts is shown to accurately describe the doping behavior of Te, Zn, Sn, Ge, Si, and C and the formation and annealing of the deep level denoted EL2 (assumed to be the arsenic antisite defect AsGa) in melt- and solution-grown crystals. The model provides a much more comprehensive and accurate description of dopant solubility than the widely cited Schottky barrier model of bulk nonequilibrium dopant incorporation. It is unambiguously shown that partial autocompensation of donor dopants by the donor–gallium vacancy acceptor complex occurs for both group IV and group VI donor dopants. The deduced concentrations of arsenic vacancies grown into the crystal during melt growth are shown to be in excellent agreement with values determined by titration and by density/lattice parameter measurements. The obtained data are used to plot the Ga–As solidus. Due to the presence of charged native point defect species (notably, VAs+), the free-carrier concentration at high temperatures is greater than the intrinsic concentration. The calculated concentration is shown to be in excellent agreement with published experimental data. The utility of an equilibrium thermodynamic model in seeking an understanding of doping behavior under conditions of high supersaturation, such as occur with organometallic vapor phase epitaxy and molecular beam epitaxy, is demonstrated. Finally, some suggestions are made as to the likely native point defect equilibria in indium phosphide.

Do Arsenic Interstitials Really Exist in As-Rich GaAs?

“…It is not clear whether the lattice expansion observed in bulk GaAs can be entirely explained by the As Ga defects known to be present. However, it appears highly probable that the As i concentration and thus the phase range in bulk GaAs is smaller than previously believed [18].…”

“…Our calculations indicate that such models might lead to significant errors by estimating the influence of a particular point defect on the lattice expansion. X-ray diffraction experiments have been used to estimate As i concentrations also in As-rich as-grown bulk GaAs on the order of some 10 19 cm 23 [17], thus indicating a deviation from exact stoichiometry in the same range [18]. It is not clear whether the lattice expansion observed in bulk GaAs can be entirely explained by the As Ga defects known to be present.…”

Si-Doped InAs/GaAs Quantum Dot Solar Cell with Alas Cap Layers

“…Secondly, a further gradual decrease in the current density with increasing doping is observed amongst the doped QDSCs. This is likely to be due to the point defects formed by Si dopants substituting Ga and As or existing as interstitials [22], [23]. Although Si doping has a negative impact in the current density, an enhancement of the VOC is observed with moderate doping density, which is likely to be due to the moderate Si doping passivating the defect states.…”

Review—Dopant Selection Considerations and Equilibrium Thermal Processing Limits for n+-In0.53Ga0.47As

“…Point defect limited activation.-Perhaps the best evidence against the chemical solubility limited and amphoteric limited compensation of dopants at high doping concentrations is the preponderance of evidence for point-defect limited activation in the III-V arsenides.. [83][84][85][86] The columbic attraction of positively charged dopant species with negatively charged vacancies species may result in the creation of inactive vacancy-dopant complexes. The amphoteric native defect model proposed by Walukiewicz [87][88][89] and experimental DFT calculations suggest that with heavy n-type doping the Fermi level shifts toward the conduction band and there is a resultant decrease in the enthalpy of formation for negatively charged V III .…”