HR-XRD curves of the selected samples. The compositions of the films were independently determined by SIMS.
Experimentally measured (solid circles with error bars) and simulated SAW velocities in the (upper panel) and (lower panel) directions. Simulation A uses elastic constants calculated as a linear interpolation between GaAs and GaN, whereas the parameters for simulations B and C are obtained using the elastic constant bowing coefficients of Ref. 6. Simulation D is similar to simulation A but uses a different set of elastic constants for GaAs (see Table I for details).
Variation of the simulated SAW velocities in the (solid line) and (dashed line) directions as a function of for the sample with . and are calculated as in simulation C (see Table I). The horizontal lines indicate the experimentally measured velocities. The triangles indicate the points corresponding to simulation C in Fig. 2.
Parameters used to obtain the elastic constants of for simulations A, B, C, and D. The elastic constants for are obtained from Eq. (1) using the elastic constants of GaAs and cubic GaN (given in the first three lines) and the bowing coefficients (given in the last three lines). Both and are in units of gigapascal.
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