Growth of modulation-doped GaAsAlGaAsquantum wires on V-groove patterned substrates

In order to achieve modulation-doped V-groove quantum wires for transport measurements, two different combinations of precursor groups have been tested: TMGa, TMAl and AsH3(set 1) and TEGa, dimethylethylaminealane (DMEAAl) and AsH3(set 2). Perfect selectivity of growth on SiO2masked substrates was obtained for set 1 and quantum wires were formed with lateral dimensions of 20 nm. However, selective epitaxy results in large local growth rate variations in areas of different SiO2surface coverage, complicating the design of modulation-doped structures. Using precursor set 2, growth is not selective. Crystalline regions on unmasked areas join smoothly the polycrystalline film growing with a similar growth rate on SiO2masked regions. The result is a growth rate independent of the local substrate patterns. Since the semi-insulating polycrystalline film does not degrade the quality of crystalline regions, these samples exhibit the first magnetotransport measurements that clearly indicate the existence of a 2DEG in our V- and U-groove structures. As a result we are able to define a layer structure that combines the specific advantages of precursor set 1 and 2 for future work.