Effect of sample size on simulations and measurements of the phase transition in ( GaAs ) 1 − x Ge 2 x and related alloys

Monte Carlo simulations have been made of the growth of (GaAs) 1 - x Ge 2 x in a direction by using the Davis-Holloway model with various sample sizes. Small samples give overestimates of the zinc blende order in thevicinity of the zinc blende to diamond phase transition. This is due to inadequate sampling over the mixture of phase and antiphase domains of GaAs that exists in this region. The effect is relevant to experimental determination of the critical composition at which the phase transition occurs because x-ray measurements on thin films are subject to significant limitations on sample size. Consequently experimental measurements will give overestimates of the Ge concentration at which the phase transition occurs because the zinc blende order will appear to exist beyond this point. These results also apply to other alloys between group III-V and group IV semiconductors and similar effects are to be expected with other growth directions that give a phase transition.