P. A. Postigo

Transition from self‐organized InSb quantum‐dots to quantum dashes

We have grown self‐organized InSb quantum dots on semi‐insulating InP (001) substrates by molecular beam epitaxy. We studied the size dependency of the uncapped InSb quantum dots on the nominal thickness of the deposited InSb by atomic force microscopy. The dot sizes have a pronounced minimum at about 2.2 monolayers of InSb. After a nominal thickness of 3.2 monolayers we observe a drastic change of the dot shape, from quantum dots to quantum dashes. From there on the dots grow in a quasicylindric shape aligned in the (110) direction.We have grown self‐organized InSb quantum dots on semi‐insulating InP (001) substrates by molecular beam epitaxy. We studied the size dependency of the uncapped InSb quantum dots on the nominal thickness of the deposited InSb by atomic force microscopy. The dot sizes have a pronounced minimum at about 2.2 monolayers of InSb. After a nominal thickness of 3.2 monolayers we observe a drastic change of the dot shape, from quantum dots to quantum dashes. From there on the dots grow in a quasicylindric shape aligned in the (110) direction.

Enhanced quantum efficiency of Ge solar cells by a two-dimensional photonic crystal nanostructured surface

A single-junction germanium solar cell with a photonic crystal nanostructured surface has been developed. The solar cell comprises a Ge p-n junction and an InGaP window layer. The InGaP window layer has been nanopatterned with an extended photonic crystal structure consisting on a triangular lattice of holes with submicronic sizes. Enhancements of the external quantum efficiency of 22% for a wide range of wavelengths and up to a 46% for specific wavelengths have been measured, which implies an increase in photocurrent between 11% and 22%. A clear correlation with the area of photonic crystal patterned has been observed.

Epitaxial lateral overgrowth of InP on Si from nano-openings: Theoretical and experimental indication for defect filtering throughout the grown layer

We present a model for the filtration of dislocations inside the seed window in epitaxial lateral overgrowth (ELO). We found that, when the additive effects of image and gliding forces exceed the d ...

Coupled-cavity two-dimensional photonic crystal waveguide ring laser

Coupled-cavity hexagonal ringlike photonic crystal lasers are fabricated as a class of single mode photonic crystal laser light sources. The structures are formed by placing one missing hole nanocavity (H1 type) between each two segments at 60° that form the hexagonal ringlike photonic crystal laser. The H1 cavities act as a mode filter, clamping the frequency of emission of the laser device. The emission frequency in these rings with cavities varies as the filling factor is changed, allowing the tuning of the laser emission. Stable single mode lasing occurs with side mode suppression greater than 20dB. This kind of devices may be used as an efficient selective filter of modes and may have important applications in future photonic devices for optical communications and optical sensing.

Optical absorption enhancement in a hybrid system photonic crystal – thin substrate for photovoltaic applications

A hybrid approach for light trapping using photonic crystal nanostructures (nanorods, nanopillars or nanoholes) on top of an ultra thin film as a substrate is presented. The combination of a nanopatterned layer with a thin substrate shows an enhanced optical absorption than equivalent films without patterning and can compete in performance with nanostructured systems without a substrate. The designs are tested in four relevant materials: amorphous silicon (a-Si), crystalline silicon (Si), gallium arsenide (GaAs) and indium phosphide (InP). A consistent enhancement is observed for all of the materials when using a thin hybrid system (300 nm) even compared to the non patterned thin film with an anti-reflective coating (ARC). A realistic solar cell structure composed of a hybrid system with a layer of indium tin oxide (ITO) an ARC and a back metal layer is performed, showing an 18% of improvement for the nanostructured device.

Room temperature continuous wave operation in a photonic crystal microcavity laser with a single layer of InAs/InP self-assembled quantum wires

We present continuous wave laser emission in a photonic crystal microcavity operating at 1.5 microm at room temperature. The structures have been fabricated in an InP slab including a single layer of self-assembled InAs/InP quantum wires (QWrs) as active material. Laser emission in air suspended membranes with thresholds of effective optical pump power of 22 microW and quality factors up to 55000 have been measured.

Raman scattering of InSb quantum dots grown on InP substrates

In this paper we present the Raman scattering of self-assembled InSb dots grown on (001) oriented InP substrates. The samples were grown by pulsed molecular beam epitaxy mode. Two types of samples have been investigated. In one type the InSb dots were capped with 200 monolayers of InP; in the other type no capping was deposited after the InSb dot formation. We observe two peaks in the Raman spectra of the uncapped dot, while only one peak is observed in the Raman spectra of the capped dots. In the case of the uncapped dots the peaks are attributed to LO-like and TO-like vibration of completely relaxed InSb dots, in agreement with high resolution transmission electron microscopy photographs. The Raman spectra of the capped dot suggest a different strain state in the dot due to the capping layer.

Room Temperature, Continuous-Wave Coupled-Cavity InAsP/InP Photonic Crystal Laser with Enhanced Far-field Emission Directionality

We demonstrate room temperature, continuous-wave lasing with enhanced far field emission directionality in coupled-cavity photonic crystal lasers, made with InAsP/InP quantum well material. These surface-emitting lasers can have a very low effective threshold power of 14.6 μW, with a linewidth of 60 pm, and 40% of the surface emitted power concentrated within a small divergence angle of ±30°.

Photonic band gaps in a two-dimensional hybrid triangular-graphite lattice.

This study investigates the dispersion relation of two dimensional photonic crystals conformed in a hybrid triangular-graphite configuration. This lattice includes, as limiting cases, two major well-known structures, the triangular and the graphite lattices. The analysis has been carried out by using preconditioned block-iterative algorithms for computing eigenstates of Maxwells equations for periodic dielectric systems, using a plane-wave basis. We present the evolution of the so-called gap maps as a function of the radii of the structures. We conclude that a number of gaps exist for both TM and TE polarizations. We also predict the appearance of sizeable complete band gaps for structures the can be achieved using present fabrication capabilities.

Electrical and optical properties of undoped InP grown at low temperature by atomic layer molecular beam epitaxy

The electrical and optical properties of undoped InP layers grown at low temperatures by solid source atomic layer molecular beam epitaxy are investigated. Phosphorus surface coverage during epitaxy is controlled by monitoring the evolution of reflection high‐energy electron diffraction pattern during growth. An accurate phosphorus supply by means of a valved cracking phosphorus cell is employed. The relation between phosphorus incorporation and the electronic properties of the epilayers is examined, and it is found that, at a substrate temperature of 340 °C, residual electron concentration increases linearly with phosphorus flux. Residual doping of InP layers grown at 340 °C has been reduced down to 1×1016 cm−3, and Hall mobilities of 3260 cm2/V s at 300 K and 14 830 cm2/V s at 65 K are reported. Low‐temperature photoluminescence of low background doping layers is dominated by near band transitions.