Origin and improvement of interface roughness in AlGaAs/GaAs heterostructures grown by molecular beam epitaxy

We show that the likely reason of interface roughness of AlxGa1−xAs/GaAs heterostructures is the surface segregation of background impurities present in the AlGaAs layer. The roughness increases with x and is worse for x=1. In our system, Al is considered to be the main source of impurities in AlGaAs. When grown using a less pure Al source, AlxGa1−xAs/GaAs interfaces show waviness with wavelength ranging from a few hundred to few thousand Å even for x=0.1. Such wavy AlGaAs/GaAs interfaces were not observed when a purer Al source was used irrespective of the AlGaAs thickness, value of x, growth rate, growth temperature (<630 °C), As4:Ga flux ratio, and other growth conditions. The AlAs/GaAs interface smoothness was further improved by using 2° to 4° off (100) towards 〈111〉A GaAs substrates, and by incorporating thin layers of GaAs at regular intervals in AlAs.