  Two fundamental extensions to the function of previously described fully
field effect two-dimensional (2D) electron heterostructures are presented:
First, using the same basic heterostructure design of lithographically defined
contacts overlain by both an insulating layer and top-gate employed for
electron systems, appropriate contact material allows a high mobility 2D hole
layer to be populated. Second, a simple method for producing mesoscopic
structures in these devices is presented in which small-scale metallic patterns
are placed on the heterostructure under the insulating and global gate layers
which allows local carrier density tuning via the overlapping gate arrays.
Example devices using these generally applicable methods are demonstrated.
