Atomically Precise Gallium Arsenide/aluminum Gallium Arsenide Structures by Cleaved Edge Overgrowth

There has been continuous progress in the fabrication of small semiconductor devices motivated by better performance and higher packing densities. New nanofabrication techniques and a better understanding of the physical processes at these scales are required to further reduce the size of the semiconductor devices to their fundamental limits. In this thesis, we used cleaved edge overgrowth (CEO), a new crystal growth technique, to realize atomically precise GaAs/AlGaAs structures and studied their electrical properties from both physics and engineering points of view. The lateral features of these devices are so sharp and precise that they cannot be fabricated by today's conventional lithographic techniques, such as electron-beam or x-ray lithography. Devices are fabricated using two different growth methods, liquid phase epitaxy and molecular beam epitaxy. Growth aspects of CEO for both of these crystal growth methods are presented. In particular, we studied three different CEO structures. The first one is a lateral superlattice structure where a two-dimensional electron system is modulated by an atomically precise one-dimensional superlattice potential. At low temperatures, these devices exhibit an increase in resistance after application of high electric fields. We identified the origin of this behavior by carefully monitoring changes in the two-dimensional electron density and showed that electron trapping induced by high electric fields occurs in our devices. The second one is a gated resonant tunneling structure where two-dimensional electrons tunnel through the subbands of a quantum wire. This three-terminal resonant tunneling device exhibits negative transconductance as well as negative differential resistance. Finally, the third one is a quasi-one-dimensional wire structure with an abrupt and uniform potential profile. We studied transport properties of these wires together with similar wires fabricated by lithographic techniques. Unlike lithographic wires, the CEO wires owing to the uniformity in their confinement potential do not suffer from diffusive boundary scatterings. Future applications of these devices and fabrication of other possible CEO structures are also discussed.