To form patterned GaInAs hetero-structures on GaAs, we proposed a new formation process using an amorphous As layer as a mask. The process consists of five stages: (1) A GaAs layer is grown at a low temperature about 480 degrees C on a GaAs substrate. The low-temperature-grown layer enhances In diffusion while annealing at the fifth stage. (2) An amorphous As layer is deposited on the GaAs layer as a mask. (3) Designed patterns are drawn on the amorphous As mask by electron beam (EB) lithography. (4) Metallic In is deposited on the patterned amorphous As mask. (5) The sample is annealed for two purposes: one is to re-evaporate the amorphous As mask with metallic In on it and the other is to diffuse In on bare GaAs into the low-temperature-grown GaAs layer. (6) Then, patterned GaInAs/GaAs hetero-structures are formed. In the process, the advantage to use the amorphous As mask is two-fold, i.e., the mask is easily deposited in a normal MBE chamber and is removed by only heating it at an appropriate temperature (about 350 degrees C), all in situ. (c) 2006 Elsevier B.V. All rights reserved.