Long range composition ordering and spontaneous formation of Al rich and Ga rich AlxGa1-xAs/AlyGa1-yAs superlattice were demonstrated. This was observed by cross-sectional transmission electron microscopy (TEM) in a 280 Å Al0.4GaAs quantum well laser diode heterostructure with Al0.7GaAs barriers grown on (111)B GaAs substrates. On the contrary, none of above superstructure was observed by TEM on a side-by-side grown (100) oriented substrate. More evidence is shown in the (111)B Al0.7GaAs barriers which were disordered due to a high growth temperature and did not show any superstructure. 10 K photoluminescence was shown with 32 meV redshift and a 12-times peak intensity enhancement in (111)B orientation.