Renovation of lab space

With the money from the FAEPEX project 2102/21, we could carry out some long needed renovation of the lab space. In January 2022, we renewed the chemical working places, created a common working space as well as improved the overall installations of the lab.

We will also clean out some old instruments to do a fresh restart of the area for everyone, now that we are back to the university.

Artigo em destaque

Sorry, this entry is only available in Brazilian Portuguese. For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

Artigo de membros do grupo foi escolhido pelo SPBMat como artigo em destaque. Veja aqui o texto em português.

New article by group member

Strain-based band structure engineering is a powerful tool to tune the optical and electronic properties of semiconductor nanostructures. We show that we can tune the band structure of InGaAs semiconductor quantum wells and modify the helicity of the emitted light by integrating them into rolled-up heterostructures and changing their geometrical configuration. Experimental results from photoluminescence and photoluminescence excitation spectroscopy demonstrate a strong energy shift of the valence-band states in comparison to flat structures, as a consequence of an inversion of the heavy-hole with the light-hole states in a rolled-up InGaAs quantum well. The inversion and mixing of the band states lead to a strong change in the optical selection rules for the rolled-up quantum wells, which show vanishing spin polarization in the conduction band even under near-resonant excitation conditions. Band structure calculations are carried out to understand the changes in the electronic transitions and to predict the emission and absorption spectra for a given geometrical configuration. Comparison between experiment and theory shows an excellent agreement. These observed profound changes in the fundamental properties can be applied as a strategic route to develop novel optical devices for quantum information technology.

Leonarde N. Rodrigues, Diego Scolfaro, Lucas da Conceição, Angelo Malachias, Odilon D. D. Couto, Jr, Fernando Iikawa, and Christoph Deneke

ACS Appl. Nano Mater., online (2021)
DOI: 10.1021/acsanm.1c00354

Research was supported by FAPESP and CNPq.

The article was featured by the SPBMat – here the Portuguese post.

Presentation of PIBIC project – Pedro Carneiro

For the annual PIBIC congress, Pedro made a video poster of his work: “Desenvolvimento de um experimento de quantificação da concentração de elementos por fluorescência de raios X e aplicação para o estudo de modelos de epilepsia em roedores”.

Presentation of PIBIC project – Gabriel Gomes

For the annual PIBIC congress, Gabriel made a video poster of his work “Fabricação e caracterização de membranas baseadas em nanoestruturas semicondutoras”.

New article by group member: Band structure engineering in strain-free GaAs mesoscopic structures

We investigate the optical properties of strain-free mesoscopic GaAs/Al(x)Ga(1-x)As structures (MGS) coupled to thin GaAs/A(x)Ga(1-x)As quantum wells (QWs) with varying Al content (x). We demonstrate that quenching the QW emission by controlling the band crossover between AlGaAs X-point and GaAs Gamma-point gives rise to long carrier lifetimes and enhanced optical emission from the MGS. For x = 0.33, QW and MGS show typical type-I band alignment with strong QW photoluminescence emission and much weaker sharp recombination lines from the MGS localized exciton states. For x >= 0.50, the QW emission is considerably quenched due to the change from type-I to type-II structure while the MGS emission is enhanced due to carrier injection from the QW. For x >= 0.70, we observe PL quenching from the MGS higher energy states also due to the crossover of X and Gamma bands, demonstrating spectral filtering of the MGS emission. Time-resolved measurements reveal two recombination processes in the MGS emission dynamics. The fast component depends mainly on the X-Gamma mixing of the MGS states and can be increased from 0.3 to 2.5~ns by changing the Al content. The slower component, however, depends on the X-Gamma mixing of the QW states and is associated to the carrier injection rate from the QW reservoir into the MGS structure. In this way, the independent tuning of X-Gamma mixing in QW and MGS states allows us to manipulate recombination rates in the MGS as well as to make carrier injection and light extraction more efficient.

Vanessa Ors Gordo, Leonarde Nascimento Rodrigues, Floris Knopper, Ailton J Garcia, Fernando Iikawa, Odilon D. D. Couto Jr. and Christoph Deneke

Nanotechnology 31, 255202 (2020)