| Abstract Scope |
III-V compound semiconductor epitaxially grown on silicon has attracted interest due to its applications in integration of optoelectronic devices with silicon-based microelectronics. In the present study, we have investigated the formation and optical properties of InAs/GaAs nano/micro structures grown on silicon by selective area epitaxy. The starting wafers are (001) and (111) oriented silicon substrates. First, a 60nm thick SiO<SUB>2</SUB> layer is thermally grown as mask. Arrays of holes with diameters ranging from 400nm to 1μm are then patterned on these substrates by stepper and subsequent dry etching. After proper cleaning procedures, growth is performed in Molecular Beam Epitaxy (MBE) chamber. Substrate temperature is shown to strongly affect the morphology and selectivity of GaAs grown on the patterned silicon substrates. In the silicon (111) case, at 550°C, almost no selectivity is observed and the deposited GaAs shows an amorphous or polycrystalline feature. At 600°C, hexagonal shape crystals are formed at the patterned nanohole sites, showing enhanced material quality. However, the selectivity is not perfect as GaAs can be seen on SiO<SUB>2</SUB> surface. Complete selective growth is achieved at 630°C with very evident faceting, indicating single crystalline growth, although defects can be observed on some of the crystals. Above 670°C, desorption dominates under the applied arsenic overpressure and therefore no material is deposited. At optimal growth temperature, dimension of the selectively grown GaAs crystal can be as large as ~1μm with clear {011} facets as top surface and side walls. Samples grown with different deposition time reveal the time evolution picture of growth. At the beginning stage, GaAs nucleates at the edge of the circular patterns. These nanocrystals then incorporate more material and expand to fill the patterned holes as growth proceeds both vertically and laterally. Transmission Electron Microscopic (TEM) image shows that misfit dislocations and stacking faults exist in the patterned hole area. However, the laterally grown material on top of SiO<SUB>2</SUB> is almost dislocation free. Based on the selectively grown GaAs structure, GaAs/InAs/GaAs structure is realized with 2 monolayers’ deposition of InAs. The growth mode of InAs on GaAs base material is not clear. One possible structure formation mechanism could be patterned quantum dots. Photoluminescence measurement shows a strong peak centered at ~1200nm at 80K. The relatively broad linewidth is probably due to non-uniform growth of InAs layer. Work supported by KACST. |