“…AlAs is an indirect gap material with the minima of the conduction band at the X points of the Brillouin zone, whereas in GaAs the minimum is at the Γ point. There have been several earlier studies of tunneling through X-valley states [10,11,12,13,14,15,16], including investigations of the tunneling through donor states associated with the X conduction band minima [17,18,19,20,21,22,23].…”