III. Application of the Model for Description of Experimental Data on Impact of Growth Conditions on Composition of Solid Solution GaPxAs1-X

The effects of TS, density of As₂ (JAs₂), P₂ (JP₂) molecule fluxes and density of Ga (JGa) atom fluxes on incorporation of arsenic and phosphorus with MBE of solid solution Ga P_xAs_1‑x(001) were experimentally investigated. The data were obtained for the following range: TS from 400С to 600С; growth rates (V_g) from 0.25 to 2,5 μm per hour; ratios 2×JAs₂/JGa from 0.5 to 10; ratios 2× JP₂/JGa from 1 to 16. Under these epitaxy conditions, gallium incorporation coefficient is equal to 1, and therefore, growth rate of layers is specified by the value of gallium atom flux. Phosphorus fraction in the film is determined by X-ray swing curves.

Figs. 1, 2 and 3 present the most important empirical dependencies obtained from the experiment.

Fig. 1. Dependence of sas/sp on 2×jas₂/jga (fig. 1а) and on 2×jp₂/jga (fig. 1b) at jga=6.26×10¹⁴ cm^-2с^-1 and ts =500c (circles)

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It can be concluded from Figs. 1a and 1b that in case of MBE of solid GaP_xAs_1‑x(001) solution relation of arsenic incorporation coefficient to phosphorus incorporation coefficient SAs/SP grows both with increase in JAs₂ to JGa relation and with increase in JP₂ to JGa relation. The circles correspond to the experimental data; the dash lines show the dependencies constructed on the basis of the model described above. The research of impact of JGa on composition of the solid structure shows that the dependence of SAs/SP relation on density of Ga atom flux (at constant values TS, JAs₂ and JP₂) is non-monotonic. As seen from the figure, there is a range of values JGa, in which relation of arsenic incorporation coefficient to phosphorus incorporation coefficient decreases with decrease in growth rate. Such a behavior of the relation between incorporation coefficient cannot be predicted on the basis of the dependencies presented in Fig. 1 Indeed, when JGa decreases, relation of molecular fluxes of V and III group elements increase. Therefore, increase in relation SAs/SP can be also expected (see. the dashed line in Fig. 2 constructed on the basis of the empirical relations from [5]). The stars show SAs/SP values calculated on the basis of our model, with TS, JAs₂, JP₂ and JGa values known from the experiment. Such a behavior of the relation presented in Fig. 2 may be explained the fact that growth rate and relation of flues of V and III group elements are independent factors that have an influence on the formation process for the composition of the solid solution.

Fig. 2. Dependence of SAs/SP on JGa (and growth rate V_g, corresponding to density of flux JGa)

Fig. 3 shows the dependence of phosphorus fraction in solid solution GaP_xAs_1‑x(001) on TS. The circles stand for the experimental data; the stars show phosphorus fractions calculated on the basis of our model, with TS, JAs₂, JP₂ and JGa values known from the experiment. Our data qualitatively match the data of studies [6], [7].

Fig. 3 Dependence of fraction of phosphorus x in solid solution GaP_xAs_1-x on TS. The data were obtained at JGa =6.26×10¹⁴cm^‑2s^‑1, JAs₂/JGa 1.6 and JAs₂/JP₂ 0.44.

The above-mentioned experimental data on impact of V_g on composition of solid GaP_xAs_1‑x(001) solution and the conflicting data found in the literature cannot be explained by the existing kinetic growth models for A^IIIB^V compounds and their solid solutions. Our kinetic model for formation of the composition of solid GaP_xAs_1-x(001) solution is used in the next section for resolution of conflicts existing in the literature.