Congruent evaporation temperature of molecular beam epitaxy grown GaAs (001) determined by local droplet etching

摘要

The congruent evaporation temperature T_c of GaAs (001) is critical for many technological processes and is fundamental to the control and stability of Ga droplets for quantum structure fabrication. We apply the technique of local droplet etching (LDE) to measure T_c for technologically important molecular beam epitaxy (MBE) grown GaAs (001). Below T_c, Ga droplets deposited on the surface shrink and form nanoholes via LDE and thermal widening. Above T_c, droplets grow by capturing excess Ga. From the transition between both regimes, we determine T_c = 680± 10 ℃. Additionally, we find that the nanohole/droplet densities follow an Arrhenius-type temperature dependence with an activation energy of 1.31 eV. The method probes the stability of pre-existing droplets formed by deposition and so avoids the complication of nucle-ation barriers and readily allows the measurement of T_c for technologically important planar GaAs surfaces in any standard MBE system.