Novel GaAs surface phases via direct control of chemical potential

Using in situ surface electron microscopy, we show that the surface chemical potential of GaAs (001), and hence the surface phase, can be systematically controlled by varying temperature with liquid Ga droplets present as Ga reservoirs. With decreasing temperature, the surface approaches equilibrium with liquid Ga. This provides access to a regime where we find phases ultrarich in Ga, extending the range of surface phases available in this technologically important system. The same behavior is expected to occur for similar binary or multicomponent semiconductors such as InGaAs.