Gallium desorption from (Al,Ga)As grown by molecular beam epitaxy at high temperatures

Abstract

We report on a detailed study by cross-sectional transmission electron microscopy (XTEM) of gallium desorption from (Al,Ga)As structures grown by molecular beam epitaxy (MBE) at substrate temperatures in the range 680–730°C. The Ga desorption rate ( D r) depends only on substrate temperature, with an activation energy, E a for re-evaporation of 2.56 eV, comparable to E a for Ga evaporation from liquid gallium. The presence of aluminum has no measurable influence on D r except where the desorbing gallium flux exceeds the incident flux ( D rå G r), when a few monolayers of residual GaAs can be detected on an AlAs surface. No As 4 overpressure dependence has been observed. In practice, therefore, multilayer structures of (Al,Ga)As with controlled thicknesses and compositions can be grown with As 4 in the temperature regime investigated by making a constant allowance for D r, irrespective of the compositional fraction of the (Al,Ga)As.