R. M. S. Kawabata

InAs quantum dot growth on AlxGa1-xAs by metalorganic vapor phase epitaxy for intermediate band solar cells

InAs quantum dot multilayers have been grown using AlxGa1−xAs spacers with dimensions and compositions near the theoretical values for optimized efficiencies in intermediate band photovoltaic cells. Using an aluminium composition of x = 0.3 and InAs dot vertical dimensions of 5 nm, transitions to an intermediate band with energy close to the ideal theoretical value have been obtained. Optimum size uniformity and density have been achieved by capping the quantum dots with GaAs following the indium-flush method. This approach has also resulted in minimization of crystalline defects in the epilayer structure.

Improved optical properties of InAs quantum dots for intermediate band solar cells by suppression of misfit strain relaxation

The properties of InAs quantum dots (QDs) have been studied for application in intermediate band solar cells. It is found that suppression of plastic relaxation in the QDs has a significant effect on the optoelectronic properties. Partial capping plus annealing is shown to be effective in controlling the height of the QDs and in suppressing plastic relaxation. A force balancing model is used to explain the relationship between plastic relaxation and QD height. A strong luminescence has been observed from strained QDs, indicating the presence of localized states in the desired energy range. No luminescence has been observed from plastically relaxed QDs.

Exploring Parity Anomaly for Dual Peak Infrared Photodetection

In this paper, we show a superlattice quantum well infrared photodetector (S-QWIP) grown by metal-organic vapor phase epitaxy with two narrow photocurrent peaks in the mid infrared range due to transitions between the ground state from a quantum well and two excited states localized in the continuum. The structure composed of InGaAs/InAlAs quantum-well lattice matched to InP with a central quantum well acting as an artificial defect. The potential profile is carefully chosen to explore the parity anomaly of the continuum localized states and also to reduce the thermoexcited electrons decreasing the dark current. The photocurrent spectrum shows two peaks with transition energies of 300 and 460 meV (Δλ/λ of 0.13 and 0.12) at 12 K. The peak detectivity is 1.23×1010 Jones at 30 K and +5 V. When compared with a regular multiquantum well sample designed to generate photocurrent at the same wavelength, the S-QWIP shows an increase of 15 K on its background-limited performance temperature and a lower dark current for temperatures above 200 K.

Simultaneous positive and negative photocurrent response in asymmetric quantum dot infrared photodetectors

We study the influence on the photocurrent of the final state in bound-to-quasibound transitions in self-assembled quantum dot infrared photodetectors. We investigate two structures designed to explore different mechanisms of carrier extraction and therefore achieve a better insight on these processes. We observe photocurrent in opposite directions, with positive and negative sign, for different incident frequencies at the same applied external electric field. This phenomenon is attributed to the asymmetry of the potential barriers surrounding the quantum dots.

Inteligência Computacional Aplicada à Síntese de Semicondutores Quaternários InAlGaAs

André Sousa Figueiredo Silva∗, Artur M. Mota Costa∗, Fernando Carvalho Coelho∗, Omar Paranaı́ba Vilela Neto∗, Rudy M. Sakamoto Kawabata†, Patrı́cia L. Souza† e Maurı́cio Pamplona Pires‡ ∗Departamento de Ciência da Computação UFMG Belo Horizonte, MG, Brasil Email: andresfs,artur.costa,fccoelho,omar@dcc.ufmg.br †LabSem Centro de Telecomunicações CETUC PUC-Rio Rio de Janeiro, RJ, Brasil E-mail: rudykawa,plustoza@cetuc.puc-rio.br ‡Instituto de Fı́sica UFRJ Rio de Janeiro, RJ, Brazil E-mail: pires@if.ufrj.br

Exceptionally Narrow-Band Quantum Dot Infrared Photodetector

InGaAlAs/InGaAs/InGaAlAs/InAs/InP quantum-dot structures have been investigated for the development of infrared photodetectors capable of generating photocurrent peaks exceptionally narrow for sharp wavelength discrimination. Our specially designed structure displays a photocurrent peak at 12

Vendo o invisível: experimentos de visualização do infravermelho feitos com materiais simples e de baixo custo

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Resonance Modes in InAs/InGaAlAs/InP Quantum Dot Microdisk Resonators

with a full width at half maximum, limited by inhomogeneous broadening, of only 4.5 meV. In agreement with two independent energy level calculations, we attribute this peak to photon absorption between InAs quantum dot bound states, followed by a three step carrier extraction mechanism in which the coupling to the adjacent InGaAs quantum well is a key feature. The possible role played by intraband Auger scattering, multiphoton sequential absorption and tunneling in generating the observed current peak is also addressed.

A proposal for Intermediate Band Solar Cells with optimized transition energy - InAs QD / AlGaAs

Utilizando materiais e equipamentos simples e de facil obtencao no dia a dia, apresentamos neste trabalho duas experiencias com a intencao de auxiliar a introducao experimental ao espectro eletromagnetico. Particular enfase e dada a faixa espectral do infravermelho proximo e suas aplicacoes no cotidiano. A fim de visualizar essa regiao do espectro, uma webcam foi devidamente alterada de forma a tornar-se sensivel a tal radiacao. Na primeira parte deste trabalho, fazemos uma introducao sobre os emissores e sensores de radiacao infravermelha. Na segunda parte, apresentamos os experimentos e os resultados obtidos.