More about Diffusion: Transient Diffusion and Diffusion with Reaction

ABSTRACTThe diffusion of implanted p-type dopants in GaAs often exhibits transient effects during annealing. This diffusion can greatly affect device performance and must be understood in order to create accurate, physically based process modeling simulation tools for compound semiconductors. The transient diffusion is believed to be related to defects created during implantation, but a direct correlation between implant damage and dopant redistribution has been difficult to establish. Results are presented in this paper of experiments designed to gain insights into the fundamental mechanisms underlying the relationship between defects and diffusion. Many anomalies in previous data are the result of implanting dopants under poorly controlled conditions, particularly implant dose rate and temperature. Special care was taken in this work to ensure that the implants were performed under well controlled conditions. Al was co-implanted with Mg and Be to study the effect of implant damage without affecting the position of the Fermi level. A correlation was found between the initial transient diffusion observed in low dose Be implants and the presence of dislocation loops. This may present a viable method for suppressing diffusion of implanted Be. SIMS profiles of Mg and Al co-implants were anomalous and difficult to interpret. Cap failure, dopant segregation to the surface and/or defects may be responsible for the discrepancies in the data. P-type doping appears to stabilize dislocation loops, probably by increasing the concentration of positively charged Ga interstitials. RBS measurements of implanted Mg indicates a link between damage production, implant dose rate, and diffusion. This result agrees with previous work on damage production in Si implanted GaAs.

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Meridional Circulation, Turbulence, and Diffusion Processes in Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100080477 ◽

1976 ◽

Vol 32 ◽

pp. 109-116 ◽

Cited By ~ 1

Author(s):

S. Vauclair

Keyword(s):

Convection Zone ◽

Diffusion Processes ◽

Meridional Circulation ◽

Diffusion Time ◽

Work In Progress ◽

First Results ◽

Stellar Envelopes ◽

And Diffusion ◽

Turbulence And Diffusion ◽

Hr Diagram

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

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