Efficient carrier injection in strain-free mesoscopic GaAs structures

The fabrication of strain-free mesoscopic GaAs structures (MGS) by Ga-assisted droplet etching (see sketch below) has attracted attention of the scientific community due to the excellent optical emission characteristics with sharp emission lines associated to different excitonic states. One way to expand the MGS application perspectives is to explore band structure engineering. In this sense, type-II band-alignment offers an additional degree of freedom in order to modify the light emitting properties of this type of semiconductor nanostructure. However, the induced spatial separation between electron and hole wavefunctions has been demonstrated to lead to considerable quenching of photoluminescence (PL) emission in quantum rings grown by droplet epitaxy.

 In this work, we show that, by changing the Al concentration, we can modify the intensity and the energy range of the optical emission of the MGS. We show that, in comparison to previous works, MGS emission can be enhanced by up two orders of magnitude by controlling the coupling of the MGS with a neighboring quantum well. We present Al-rich structures with high emission intensity and long/tunable carrier lifetimes which can be interesting for future applications in solid-state optoelectronic devices and solar cells.

This work was done in collaboration with Prof. Christoph Deneke from IFGW and Prof. Leonarde Rodrigues from the University of Viçosa (UFV).

For the full text, click HERE.

Self-calibrated molecular thermometer

Heat generation on larger circuit boards is well-understood; however, at the nanoscale, the relationship
between heat and electricity remains unanswered due to lack of appropriate thermometers capable of thermal monitoring without perturbing the system. Unfortunately, temperature measurement at the submicrometer spatial range is not possible with conventional contact thermometers. A way to overcome this impasse is building microdevices with materials capable of also acting as in situ thermometers having submicrometric spatial resolution.

In collaboration with Prof. Fernando Sigoli from Unicamp and Muralee  Murugesu from the University Ottawa, we studied the optical properties of self-calibrated molecular thermometers based on single magnet molecules.  We demonstrate the feasibility of stable micrometer-scale thermometers operating in the range of 5 to 398 K.  Stability is achieved up to 7 T applied magnetic fields.

For full manuscript click HERE.

Nanostructured membranes for flexible optoelectronics

In collaboration with Prof. Christoph Deneke, we studied the optical emission of molecular beam epitaxy grown semiconductor systems on free and flexible membranes. We obtain optically active nanostructures (quantum wells) regrown on released GaAs/InGaAs/GaAs membranes used as virtual substrates. Together with our demonstrated ability to transfer thin semiconductor membranes before overgrowth to a new host substrate,  this work establishes III–V semiconductor membranes as a compliant substrate for epitaxy, allowing strain engineering of
III–V heterostructures for optical and electrical applications.

For the complete manuscript click HERE.

For the press release HERE.

 

Revealing the optical properties of two-dimensional materials

In collaboration with the Federal University of São Carlos, the University of Brasília, the University of Southampton, and the University of Nottingham, we investigated the properties of charged excitons in large-area WS2, a transition metal dichalcogenide. We investigate in details the recombination dynamics of the different excitonic complexes of the system. We show that, in particular, the neutral and singly-charged (trion) exciton dynamics are influenced by charge injection from SiO2 substrates, which contribute to a redistribution of the exciton complexes along time. The Figure below shows the time evolution of the neutral (X), trions (T1 and T2), bound (XB), and localized ecitons (LS) as the pumping (laser) power conditions are modified, demonstrating irreversible processes in the exciton emission after long exposure times and pumping power. This work contributes to the understanding of the excitonic dynamics in this new class of materials, which may be important for future optoelectronic devices in graphene-like materials.

To access to the full text, click HERE.

You can also see the web release of this work in our institute webpage.

Bimolecular recombination reviewed

Carrier recombination processes are demonstrated to be tuned by tunneling effects in a quantum well coupled to a quantum dot ensemble. Carrier density is demonstrated to affect recombination rates in a dramatic way. The understanding of the experimental results is performed by an examination of the bimolecular recombination dynamics of the system. To get the full discussion click HERE.

Oportunidade: iniciação científica

Estamos selecionando alunos com bom currículo acadêmico interessados em fazer iniciação científica em nosso laboratório. Temos bolsas de iniciação pré-aprovadas pela FAPESP dentro de nosso projeto Jovem Pesquisador, o que nos perrmite atribuí-las diretamente  a candidatos interessados. Para maiores informações, entrar em contato através do email ao lado.

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GaAs nanowires go brighter

GaAs-NWs

Semiconductor nanowires have been extensively investigated in the last few years due to their new physical properties and enormous perspectives for applications. In this work, we investigate the effects of GaAsP passivation on strained GaAs core-shell nanowires. We demonstrate that, as a result of the decrease of the density of surface states, 4 orders of magnitude more intense photoluminescense (as compared to unpassivated structures) can be achived. For more details click HERE.

Pumping single photons with SAWs

Acoustic-SPS

Surface acoustic waves (SAWs) have were employed to demonstrate high frequency (750MHz) single-photon sources (SPS). By remotely pumping electrons and holes into a GaAs quantum well, we were able to transport and inject them into quantum dots which work as efficient SPS. Our achievements represent a novel approach in the direction of high speed quantum information processing. For more details click HERE.

Welcome!

Welcome to my homepage. Here you will find information about my research, experiments, related literature, and job oportunities in our laboratory. This page is also dedicated to my teaching activities at the University of Campinas.