Antonio Rivera

Strain Balanced Epitaxial Stacks of Quantum Dots and Quantum Posts

Tesis doctoral inedita. Universidad Autonoma de Madrid, Facultad de Ciencias. (Departamento de Fisica de la Materia Condensada). Fecha de lectura: 11-11-2011

Optical Waveguides Fabricated by Ion Implantation/Irradiation: A Review Optical Waveguides Fabricated by Ion Implantation/Irradiation: A Review

Ovidio Pena-Rodriguez1,2, Jose Olivares1,2, Mercedes Carrascosa3, Angel Garcia-Cabanes3, Antonio Rivera4 and Fernando Agullo-Lopez1 1Centro de Microanalisis de Materiales (CMAM), Universidad Autonoma de Madrid (UAM), Cantoblanco, Madrid 2Instituto de Optica, Consejo Superior de Investigaciones Cientificas (IO-CSIC), Madrid 3Departamento de Fisica de Materiales C-IV, Universidad Autonoma de Madrid, Madrid 4Instituto de Fusion Nuclear, Universidad Politecnica de Madrid, Madrid Spain

Direct formation of InAs quantum dots grown on InP (001) by solid-source molecular beam epitaxy

We have developed a growth process that leads to the direct formation of self-assembled InAs quantum dots on InP(001) by solid-source molecular beam epitaxy avoiding the previous formation of quantum wires usually obtained by this technique. The process consists of a periodically alternated deposition of In and As correlated with InAs(4×2)↔(2×4) surface reconstruction changes. Based on the results obtained by in situ characterization techniques, we propose that the quantum dots formation is possible due to the nucleation of In droplets over the InAs(4×2) surface during the In deposition step and their subsequent crystallization under the As step.

Strain driven migration of In during the growth of InAs/GaAs quantum posts

Using the mechano-optical stress sensor technique, we observe a counter-intuitive reduction of the compressive stress when InAs is deposited on GaAs (001) during the growth of quantum posts. Through modelling of the strain fields, we find that such anomalous behaviour can be related to the strain-driven detachment of In atoms from the crystal and their surface diffusion towards the self-assembled nanostructures.

Metamorphic antimonides on GaAs for thermophotovoltaic devices

The growth of metamorphic III-V semiconductors on substrates of dissimilar lattice parameter is of interest for the engineering of optoelectronic devices for which the cost of the substrate would otherwise limit the applicability of the material. Such is the case of the antimonides, which are very appropriate for small band gap photovoltaics or thermophotovoltaics. To further increase the efficiency of tandem solar cells (typically based on Ge or GaAs substrates) it is necessary to integrate materials with band gap < 1.4 eV. Metamorphic InGaAs has been successfully integrated in GaAs based tandems, but requires the growth of thick step graded buffers of InGaP.i Here we present a study on the nucleation and subsequent growth of AlSb on GaAs (001), and compare our results with the more extensively studied case of GaSb on GaAs,ii, iii and the case of AlSb grown on Si.iv We have observed the nucleation of almost completely relaxed AlSb islands after 0.11 ML of AlSb. The lattice parameter of the metamorphic material is slightly smaller than that of bulk AlSb. Measuring the deformation of the substrate during growth, we have observed that residual stress accumulates due to the incomplete plastic relaxation at the interface. Transmission Electron Microscopy (TEM) images show almost all of the plastic relaxation accommodated by an array of 90° misfit dislocations at the interface (IMF). A very small fraction of the plastic relaxation is accommodated by stacking faults (in the case of AlSb) or threading dislocations (in the case of GaSb). We have observed InAs layers grown on GaSb to be quite effective filters of threading dislocations, but stacking faults in AlSb propagate undisturbed though thin InAs and GaSb layers.