Strained Si_1-xGe_x/Si Dots and Wires Grown by Selective Epitaxy

Abstract
Selective epitaxial growth of Si_1-xGe_x was studied with the aim to fabricate quantum wires and dots. The selective deposition was performed by low pressure chemicd vapor deposition with dichlorosilane and germane as precursors, at 0.1 Torr and 700°C in a radiation heated, cold wall, high vacuum, quartz reactor. Dislocation free strained dots and wires could be grown much thicker than the critical thickness for unpatterned area, because the critical thickness by formation of misfit dislocations increases when the window dimension is reduced. For x up to 20% it was found that for 10x10µm² dots the critical thickness increases by more than 4 times. The tendency of facet formation was exploited to realize laterally confined multiple quantum well dots and wires with size down to 50 nm. Besides the emission from the (100) quantum well layers excintonic emissions from quantum well layers from flat {110} facets and from islands in the (100) and {311}facets were detected. All dots and wires luminecse stronly down to the lowest achieved dimension of 50 nm, the integral intensity exceeding that from the substrate.