The concept of leaky electronic states in the continuum is used to achieve room temperature operation of photovoltaic superlattice infrared photodetectors. A structural asymmetric InGaAs/InAlAs potential profile is designed to create states in the continuum with the preferential direction for electron extraction and, consequently, to obtain photovoltaic operation at room temperature. Due to the photovoltaic operation and virtual increase in the bandoffset, the device presents both low dark current and low noise. The Johnson noise limited specific detectivity reaches values as high as 1.4 × 1011 Jones at 80 K. At 300 K, the detectivity obtained is 7.0 × 105 Jones.

We study the controlled introduction of defects in GaMnAs by irradiating the samples with energetic ion beams, which modify the magnetic properties of the DMS. Our study focuses on the low-carrier-density regime, starting with as-grown GaMnAs films and decreasing even further the number of carriers, through a sequence of irradiation doses. We did a systematic study of magnetization as a function of temperature and of the irradiation ion dose. We also performed insitu room temperature resistivity measurements as a function of the ion dose. We observe that both magnetic and transport properties of the samples can be experimentally manipulated by controlling the ion-beam parameters. For highly irradiated samples, the magnetic measurements indicate the formation of magnetic clusters together with a transition to an insulating state. The experimental data are compared with mean-field calculations for magnetization. The independent control of disorder and carrier density in the calculations allows further insight on the individual role of this two factors in the ion-beam-induced modification of GaMnAs.

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.

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Utilizando materiais e equipamentos simples e de fácil obtenção no dia a dia, apresentamos neste trabalho duas experiências com a intenção de auxiliar a introdução experimental ao espectro eletromagnético. Particular enfaseé dadaà faixa espectral do infravermelho próximo e suas aplicações no cotidiano. A fim de visualizar essa região do espectro, uma webcam foi devidamente alterada de forma a tornar-se sensível a tal radiação. Na primeira parte deste trabalho, fazemos uma introdução sobre os emissores e sensores de radiação infravermelha. Na segunda parte, apresentamos os experimentos e os resultados obtidos. Palavras-chave: infravermelho, espectro eletromagnético, câmera digital, webcam, ensino de física experimental.By using ordinary and low cost equipments, we present in this work two experiments intending to improve the experimental introduction into the electromagnetic spectrum. Particular emphasis is given to the infrared range of the spectrum and its application in the daily life. In order to see the infrared, a digital camera was properly modified becoming sensitive to this particular range of the electromagnetic spectrum. In the first part of the work, we give a brief introduction on infrared sensors and emitter and in the second part we show the experiments and the results. Keywords: infrared, electromagnetic spectrum, digital camera, webcam, teaching of experimental physics. IntroduçãoNossa percepção do mundo que nos cerca provém dos 5 sentidos que conhecemos: olfato, paladar, tato, audição e visão. Sendo que a visãoé considerada o mais nobre dentre os 5, com tamanha complexidade que muitos opositores da teoria de evolução de Darwin utilizamna como argumento favorávelà teoria do design inteligente. 2Analisando com atenção oórgão responsável por esse sentido, podemos objetivamente defini-lo como um sensor de luz capaz de distinguir as cores. Contudo, aprenderemos mais a frente que a faixa que compreende a luz chamada visível (do violeta até o vermelho) constitui apenas uma pequena porção do espectro eletromagnético (Fig. 1). Tal espectro envolve as ondas das transmissões de rádio, as ondas que são utilizadas no aparelho de microondas, o ultravioleta responsável pelo bronzeamento da nossa pele, e muitas outras, como a radiação infravermelha -o tópico central deste artigo.Com relaçãoà radiação infravermelha, descoberta em 1800 pelo astrônomo inglês William Herschel [1], as aplicações se dão, principalmente, naárea de imageamento. As imagens de "visão noturna" e o mapeamento de temperaturas de um corpo (Fig. 2) são exemplos de aplicações utilizadas naárea militar e na medicina, respectivamente. Além dessas, podemos citar outras aplicações como o controle remoto, sensores de presença, sensores de movimento em videogames, aparelhos para diagnóstico médico, células solares para geração de energia elétrica, telescópios capazes de ver astros distantes que não possuem luz visível própria, entre muitas outras [2].1 E-mail: micha@if.ufrj.br; danielmicha@hotmail.com.2 A menção a esse fato pseudo-científicoé apenas...

We studied the influence of the final state in a bound-to-quasibound transition in the photocurrent sign on quantum dot structures for photodetection. We measured a photocurrent with positive and a negative sign for the same external field for different wavelengths. This process can be seen for very small external applied bias voltages and when no bias is applied. For high external fields the photo excited electrons flows in the direction of the field, as expected.

Herein, two challenges are addressed, which quantum well infrared photodetectors (QWIPs), based on III-V semiconductors, face, namely: photodetection within the so-called "forbidden gap", between 1.7 and 2.5 microns, and room temperature operation using thermal sources. First, to reach this forbidden wavelength range, a QWIP which consists of a superlattice structure with a central quantum well (QW) with a different thickness is presented. The different QW in the symmetric structure, which plays the role of a defect in the otherwise periodic structure, gives rise to localized states in the continuum. The proposed InGaAs/InAlAs superlattice QWIP detects radiation around 2.1 microns, beyond the materials bandoffset. Additionally, the wavefunction parity anomaly is explored to increase the oscillator strength of the optical transitions involving higher order states. Second, with the purpose of achieving room temperature operation, an asymmetric InGaAs/InAlAs superlattice, in which the QW with a different thickness is not in the center, is used to detect infrared radiation around 4 microns at 300 K. This structure operates in the photovoltaic mode because it gives rise to states in the continuum which are localized in one direction and extended in the other, leading to a preferential direction for current flow.

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