Anisotropic electron mobilities of Al0.3Ga0.7As/InxGa1-xAs/GaAs high electron mobility transistor structures

Abstract

Anisotropic electron mobilities in Al0.3Ga0.7As/InxGa1-xAs/GaAs high electron mobility transistor structures grown using molecular beam epitaxy were studied using Hall effect measurements. The electron mobility depends on the orientation of the Hall bar in relation to the crystal axes. The lowest mobility was observed of the (011) direction. Up to an angle of 90 degrees corresponding to the (01-1) direction, the mobility increases with increasing angle. Beyond 90 degrees it decreases until it reaches its initial value again at 180 degrees . The mobility ratio mu (01-1)/ mu (011) increases with increasing width of the quantum wells of InxGa1-xAs layers for a constant x value. The mobility ratio also depends on the In content. With increasing In content of the InxGa1-xAs layer and for a quantum well width near the critical layer thickness, an increase in the mobility ratio was observed.