Nanoscale patterned growth by molecular beam epitaxy and its applications

Nanoscale patterned (nanopatterned) growth is investigated with interferometric lithography (IL) and molecular beam epitaxy (MBE). On nanoscale SiO₂ -patterned GaAs substrates, prepared by IL and dry etching, growth of GaAs, In_xGa_1−xAs quantum wells (QWs) and quantum wires (QWRs), and InAs quantum dots (QDs) is examined by MBE. Homoepitaxial selective growth of GaAs is achieved in MBE for the first time. This is enabled by a negligible sticking coefficient of Ga atoms on a SiO₂ surface or surface migration of Ga atoms from a SiO₂ surface to a nearby GaAs surface when the growth temperature is high and the Ga flux is low. The former is applied to growth of a single InAs dot in a circular open GaAs surface of a diameter ∼60 nm. The latter referred to as nanoscale selective growth is realized when the lateral dimension of SiO₂ mask is comparable to or less than the surface migration length of Ga atoms on SiO₂ surface at a given growth condition. Detailed experimental results and a model for selective growth based on the general rate equation of thin film growth are presented. With selective growth, faceting and lateral growth of GaAs over a SiO₂ mask are observed and qualitatively explained by equilibrium crystal shape. Dynamical faceting on GaAs stripes results in nanoscale faceted (nanofaceted) surfaces which consist of periodic (100) and (n11) facets. Using orientation dependent migration and incorporation (ODMI) of In atoms which preferentially migrate from (n11) sidewalls to (100) bottom facets, growth of self-aligned InAs QDs and In_xGa_1−xAs/GaAs QWs and QWRs on a nanofaceted surface are demonstrated. Several 1D stripe patterns having different periods are fabricated on a single substrate so that ODMI can induce different In composition in each period zone from a single-run growth of In_xGa_1−xAs/GaAs QWs. A multiple-wavelength emission span of about 160 nm with a center wavelength of about 1.06 μm at 77 K is achieved from different In composition In_xGa_1−x As/GaAs QWs on a single substrate. A potential application of ODMI of In atoms on a nanofaceted surface to wavelength division multiplexing transmitters is discussed.