Transport properties in a gated heterostructure with a trapezoidal AlxGa1−xAs barrier layer

By replacing the flat (Ga1−xAlx)As barrier layer with a trapezoidal AlxGa1−xAs barrier layer, a conventional heterostructure can be operated in enhancement mode. The sheet density of two-dimensional electron gas (2DEG) in the structure can be tuned linearly from N2D=0.3×1011 cm−2 to N2D=4.3×1011 cm−2 by changing the bias on the top gate. The present scheme for gated heterostructures is easy to fabricate and does not require the use of self-alignment photolithography or the deposition of insulating layers. In addition, this scheme facilitates the initial electrical contact to 2DEG. Although, the highest electron mobility obtained for the moment is limited by the background doping level of heterostructures, the mobility should be improved substantially in the future.