Arsenic Precipitate Accumulation in Alternately Si/Be Delta-Doped GaAs Grown by Low-Temperature Molecular Beam Epitaxy

Abstract

equilibrium between ionization and recombination is obtained, and the interpretation of diagnostic observations and the The available literature on electron impact ionization of ions of charge development of realistic models of these plasmas require an + 3 or greater is reviewed. Several easily used formulae are presented the classical result, the Lotz formula, and a scaled Coulomb-Born understanding Of both ionization and recombination. k l e cprescription. The available experimental cross-sections, which now tronic recombination proceeds through excited states similar include a few good quality crossed-beams measurements, are compared to those involved in excitation-autoionization. While the states with the cross-sections obtained from the formulae and, where available, involved are not exactly the same, the excitation process is with true Coulomb-Born calculations. The Lotz formula is overall found important in both the ionization and recombination events to be closest to the experimental results. However, this result is fortuitous since much of the experimental data are found to contain measurable w h~h control ionization contribution from the excitation-autoionization process not included There are additional constraints for relevance to fusion in any of the fm-"e. It appears to be more important to include plasmas. Heavy impurity atoms cannot be tolerated in tokamakestimates of the excitation-autoionization contribution to ionization type plasmas because their ions radiate energy too efficiently, It cross-sections than to improve the models of the direct ionization process. now seems unlikely that atoms with electronic configurations in plasmas.

Dual accumulation and depletion behaviors of the arsenic precipitation in low-temperature-grown Be delta-doped GaAs

“…However, when the Si and Be doping concentrations reach certain extents, opposite precipitation behaviors occur. [10][11][12] O'Hagan et al 10 first observed the existence of dense and large precipitates in the undoped regions, but loose and small precipitates in the Si-doped regions in ''superlattice'' structures of alternately undoped and ͓Si͔ϭ1 ϫ10 19 cm Ϫ3 heavily doped GaAs. Su et al 11 studied similar superlattice structures of undoped and ͓Be͔ϭ1ϫ10 19 cm Ϫ3 doped GaAs, and found that As precipitates preferentially accumulate toward the interfaces of Be-doped GaAs and the following MBE-grown undoped GaAs.…”

“…Su et al 11 studied similar superlattice structures of undoped and ͓Be͔ϭ1ϫ10 19 cm Ϫ3 doped GaAs, and found that As precipitates preferentially accumulate toward the interfaces of Be-doped GaAs and the following MBE-grown undoped GaAs. Hsieh et al 12 observed the first As precipitates accumulation on Be delta-doped planes in a LT structure consisting of alternately ͓Si͔ ϭ1ϫ10 13 and ͓Be͔ϭ1ϫ10 14 cm Ϫ2 ␦-doped GaAs. In this work, we attempt to find the transition Be sheet density, below which the Be ␦-doped planes would deplete As precipitates as generally expected, and a possible mechanism to account for the As precipitates accumulation on Be heavily doped planes.…”