ISSN:
0142-2421
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Physics
Notes:
There is a developing interest in the use of atomic plane or δ-doping to produce narrow dopant spikes in molecular beam epitaxy GaAs. It is of importance to measure the dopant profile and to determine the growth conditions that minimize dopant spreading. We have used SIMS with low-energy oxygen bombardment to study the incorporation of silicon in such layers. To aid the optimization of the SIMS depth resolution, a special δ-doped layered structure has been produced by growth at 400°C. A critical evaluation of the SIMS data for these spikes shows that the profiles are broadened entirely by sputter-induced relocation effects rather than by thermal diffusion processes. The form of these δ-spike profiles therefore represents the SIMS resolution function with our specific experimental conditions. The absolute depth resolution (ΔZ) is found to be essentially constant for eroded depths up to ∼500 nm. With the lowest probe energy (0.7 keV per atom), giving a ΔZ of 2.7 nm, at least 68% of the Si is contained within nine atomic planes. Using appropriate sample handling, a detection limit of 1 × 1016 cm-3 Si is obtained after the erosion of only ∼ 15 nm. Analysis of structures grown at normal molecular beam epitaxy temperatures indicates that significant dopant spreading takes place during growth. It is shown that a knowledge of the resolution function enables the inherent SIMS broadening errors to be removed from these measurements. Thus, when the layer growth time is deliberately increased, the Si migrational process is dominated by Fickian diffusion, with the diffusion coefficient being equal to 3.8 × 10-17 cm2 s-1 at 553°C.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/sia.740140607
