GaAs-substrate/-oxide (where 10 is the number of periods) BEMA model used in the analysis of the SE spectra; and are the layer thicknesses. A linear gradient is used for layer 1 going from the top layer to the composition of layer 2 that is a BEMA mixture of GaAs and .
(Color online) Typical AFM morphologies observed for the samples obtained upon P-for-As anion exchange at different surface temperatures, soak times, and for As-lean and As-rich surfaces.
Surface ratio derived from area ratio of the and XPS peaks for As-rich and As-lean GaAs layers exposed to at various temperatures for 10 and . The XPS takeoff angle is 20°.
(Color online) XRD rocking curves of SLs obtained by exposure of (a) As-rich surfaces and (b) As-lean surfaces of GaAs epitaxial layers to phosphorus for a fixed time of and varying the surface temperature.
(Color online) Experimental (black) and best simulated (red, lower curve) XRD spectra for SLs obtained by exposure of an As-rich GaAs surface to a phosphorus flux at for . The comparison between the XRD and ellipsometry (SE) models is also shown. “ layer thickness” refers to the overall thickness of layers where phosphorus has been incorporated.
Spectra of the imaginary, , part of the pseudodielectric functions acquired for SLs obtained by exposure of GaAs to a phosphorus flux at 420° for 10 and and at for . The inset shows the detail of the and CPs. The corresponding best-fit models with layer thickness and composition are also shown at the bottom.
(a) Second derivative spectra of the imaginary, , part of the pseudodielectric function in the region of the and CPs; (b) and spectra in the photon energy region of for SLs obtained by exposure of GaAs to a phosphorus flux at 420° for 10 and and at for .
Phosphorus content per monolayer (ML) as estimated from XRD (+) and SE (엯) analyses for P-for-As anion exchange at the As-rich GaAs surface as a function of surface temperature.
(Color online) Simulated composition from a neural network process model fitting of the data as a function of substrate temperature and soak time for the As-lean and As-rich surfaces. The variant of the different surface reconstructions is also shown. The As coverage characterizing the various surface reconstructions is also indicated to guide the reader to the different As enrichments of the surface; referring to the last two As atomic rows of the surface reconstruction, refer to the bottom As coverage and refers to the outmost As dimers.
Dependence of integrated P content on P-soak time, as estimated by SE analysis, for As-rich and As-lean GaAs epitaxial layers exposed to the flux at various temperatures. Dots are experimental points; lines are simulations according to rate equations (9) and (11).
Arrhenius-like plot of the P-for-As anion exchange for As-rich (∎) and As-lean (엯) GaAs epitaxial layers exposed to the flux for .
Thickness and composition of the two layers resulting from the P-for-As anion exchange reaction involving As-rich and As-lean surface reconstructions of GaAs epitaxial layers as determined by the fit of SE spectra according to the model sketched in Fig. 1.
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