The potential imaging performance of infrared (IR) detectors is dependent on the noise level in the detector pixels. Noise measurements at pixel level can therefore provide basic understanding of the intrinsic limitations of detectors. Accurate noise studies with measurements at different biases and with high frequency resolution can however consume a lot of time; therefore, automation of this process is necessary. In this thesis, automation of a noise measurement setup has been implemented. The noise measurement system that has been automated has proven to work for automatically acquiring noise spectra from long wavelength infrared detectors of different types, such as Quantum Well Infrared Photodetectors (QWIPs) and Type II-superlattice (T2SL) detectors. The results of these studies have been used to calculate the noise gain of the detectors. It also has been key to determine discrepancies between different QWIP fabrication batches and helped to clarify the differences in performance of the detectors from those batches. Regarding T2SL, noise measurements on detectors with big differences in dark current have been carried out. Finally, a study of the impact of pixel shape in T2sL noise has been conducted. / Bildkvaliteten hos bildgenererande infraröda (IR) detektorer påverkas av brusnivån i de enskilda pixlarna i detektormatrisen. Brusmätningar på pixelnivå kan därför ge en grundläggande förståelse för vad som begränsar detektorns prestanda. Noggranna studier av bruset, med mätningar vid olika spänningar och med hög frekvensupplösning kan dock vara väldigt tidskrävande, varför automatisering av dessa mätningar är nödvändigt.I detta examensarbete har automatisering av en brusmätuppställning för IR-detektorer utförts.Automatiseringen av brusmätsystemet har fungerat tillfredsställande och har använts för att mäta brus i olika sorters långvågiga IR-detektorer, såsom kvantbrunnsbaserade IR-detektorer (QWIP= Quantum well infrared photodetector) och typ-II supergitterbaserade IR-detektorer (T2SL = Type II superlattice).Resultaten av dessa studier har använts för att beräkna brusförstärkningsfaktorn i dessa detektorer. Studier av brusspektra från olika tillverkningsbatcher av QWIPar har varit en avgörande faktor för att förstå varför detektorprestanda varierar mellan olika batcher. För T2SL-baserade IRdetektorer har studier utförts för att avgöra inverkan av pixelformen, pixelstorlek och mörkerströmsnivå på brusnivån i dessa detektorer.

[pt] Os semicondutores III-V são amplamente investigados para a fabricação de fotodetectores de infravermelho baseados em pontos quânticos (QWIPs); no entanto, o comprimento de onda de operação é limitada pelo bandoffset dos materiais que permitem transições de infravermelho de comprimento de onda maior que 3,1 um. Para comprimentos de onda mais curto do que 1,7 um transições banda a banda são facilmente empregadas. Assim, em QWIPs III-V, o intervalo entre 1,7 e 3,1 um não pode ser alcançado tanto por transições banda-banda ou por transições intrabanda. Nesta tese uma estrutura de superrede especialmente desenhada é proposta a fim de detectar a radiação dentro desta faixa proibida. A estrutura proposta consiste numa superrede com um poço quântico central mais amplo, o qual gera uma modulação no contínuo criando minibandas e minigaps para energias acima da parte inferior da banda de condução do poço quântico, incluindo no contínuo. Com esta abordagem, a limitação de ter estados ligados apenas com energias abaixo a barreira não se mantém e é possível detectar energias mais elevadas do que o limite imposto pelo bandoffset dos materiais. Simulações teóricas para a estrutura foram realizados e medidas de absorção, corrente de escuro, e fotocorrente foram realizadas mostrando picos em 2,1 um, em estreita concordância com o valor teoricamente esperado. / [en] III-V semiconductors are extensively investigated for fabrication of quantum well infrared photodetectors (QWIPs); however the operation wavelength is limited by the bandoffset of the materials allowing infrared transitions for wavelength larger than 3.1 um. For wavelength shorter than 1.7 um band to band transitions are easily employed. Thus, in III-V QWIPs, the range between 1.7 and 3.1 um cannot be reached either by band-to-band or by intraband transitions. In this thesis a specially designed superlattice structure is proposed in order to detect radiation within this forbidden range. The structure proposed consists of a superlattice with a wider central quantum well, which generates a modulation in the continuum creating minibands and minigaps for energies above the bottom of the conduction band of the quantum well, including in the continuum. With this approach the limitation of having bound states only with energies below the barrier no longer holds and it is possible to detect energies higher than the limit imposed by the bandoffset of the materials. Theoretical simulations for the structure were performed and absorption, dark current, and photocurrent measurements were carried out showing peaks at 2.1 um, in close agreement with the theoretically expected value.

Quantum well infrared photodetectors (QWIP) utilize quantum wells of large bandgap materials to detect infrared radiation. When compared to conventional low bandgap LWIR photodetectors, the QWIP technology offers largest format thermal imagers with much better uniformity. The theoretical part of this study includes the development of a QWIP ensemble Monte-Carlo simulator. Capture paths of electrons to quantum wells are simulated in detail. For standard AlGaAs/GaAs QWIPs, at medium and high E-fields L valley quantum well (QW) is a trap for electrons which causes higher capture probability when compared with InP/InGaAs and GaAs/InGaAs QWIPs. The results suggest that high photoconductive gain observed in InP/InGaAs and GaAs/InGaAs QWIPs is not due to good transport properties of binary barrier material but due to higher &amp / #61511 / -L valley energy separation. The experimental part of the study includes the fabrication and characterization of InP/InGaAs and InP/InGaAsP QWIPs and 640x512 FPAs with the main objective of investigating the feasibility of these material systems for QWIPs. The InP/InGaAs and InP/InGaAsP QWIP detectors showed specific detectivity values above 1010 cm.Hz1/2/W (70K, f/2, background limited). The devices offer higher allowable system noise floor when compared with the standard AlGaAs/GaAs QWIP technology. It is also experimentally shown that for strategic applications LWIR InP based QWIPs have advantages over the standard QWIP technology. The InP/InGaAs 640x512 QWIP FPA reached 36 mK average NETD value at 70 K with f/1.5 optics and 10 ms integration time. The InP/InGaAsP QWIP on the other hand yielded 38 mK NETD histogram peak at 70 K with f/1.5 optics and 5 ms integration time on 320x256 window of the 640x512 FPA.

Quantum Well Infrared Photodetector (QWIP) technology is promising for the development of large format low cost single and dual/multi color infrared sensor arrays. Thanks to the mature III-V semiconductor technology, QWIP focal plane arrays (FPAs) provide high uniformity and excellent noise equivalent temperature difference (NETD) in both long wavelength infrared (LWIR 8-12 &amp / #61549 / m) and mid wavelength infrared (MWIR 3-5 &amp / #61549 / m) bands. This thesis work focuses on the development of large format single and dual color MWIR QWIP FPAs. For single band MWIR detection, we report QWIP FPAs on InP substrate as an alternative to the GaAs based MWIR QWIPs suffering from the degrading effects of lattice mismatched epitaxy. In the course of this work, epitaxial growth conditions of the device structure were optimized and 640&times / 512 AlInAs/InGaAs QWIP FPAs on InP substrate have been fabricated yielding NETD of 22 mK (f/1.5) and background limited performance (BLIP) temperature as high as 115 K In the second part, we report the first voltage tunable 640&times / 512 dual color MWIR QWIP FPA. After optimizing epitaxial growth of AlGaAs/InGaAs material system, we have designed and implemented the device structure to yield voltage tunable spectral response in two different windows in the MWIR band. The FPA provides NETDs of 60 and 30 mK (f/1.5) in colors 1 and 2. The results are very encouraging for the development of low cost dual/multi color FPAs since our approach utilizes one In bump per pixel allowing fabrication of dual color FPAs with the same process steps for single color FPAs.

Quantum Well Infrared Photodetectors (QWIPs) have the advantages of excellent uniformity and mature material properties. Thanks to these properties, large format and low cost QWIP focal plane arrays (FPAs) can be fabricated. The standard material system used for QWIP FPAs is AlGaAs/GaAs in the long wavelength infrared (LWIR) band. AlGaAs/GaAs material system has some disadvantages such as low quantum and conversion efficiencies under high frame rate and/or low background conditions. These limitations of the standard material system give rise to research on alternative material systems for QWIPs. InP/InGaAs material system is an alternative to AlGaAs/GaAs for LWIR QWIPs. This thesis focuses on the development of InP/InGaAs QWIP FPAs. A large format (640x512) LWIR QWIP FPA constructed with strained InP/InGaAs system is demonstrated with high quantum and conversion efficiencies. The FPA fabricated with the 40-well epilayer structure yielded a peak quantum efficiency as high as 20% with a broad spectral response (15%). The responsivity peak and the cut-off wavelengths of the FPA are 8.5 and ~9 um, respectively. The peak responsivity of the FPA pixels is larger than 1 A/W with a conversion efficiency as high as ~17 % in the bias region where the detectivity is reasonably high. The FPA provides a background limited performance (BLIP) temperature higher than 65 K (f/1.5) and satisfies the requirements of most low integration time/low background applications. Noise equivalent temperature difference (NETD) of the FPA is as low as 25 mK with integration times as short as 2 ms (f/1.5, 68 K).

L'imagerie infrarouge bas flux requiert des détecteurs grandes longueurs d'onde de hautes performances. Les détecteurs à puits quantiques (QWIP), de par la maturité de GaAs, la facilité à ajuster la longueur d'onde détectée sur une très large gamme et la possibilité de réaliser de larges matrices uniformes constituent d'excellents candidats pour ces applications. Afin de confirmer leur intérêt nous avons procédé à la caractérisation électro-optique fine d'un composant QWIP détectant à 15µm. Les performances mesurées ont été utilisées pour simuler celles d'une caméra basée sur ce détecteur et dédiée à un scénario faible flux et ont permis de valider la capacité de la filière QWIP à répondre à de telles missions infrarouges. Ces simulations ont aussi mis en évidence le rôle extrêmement préjudiciable joué par le courant d'obscurité. Nous avons alors mis au point une simulation basée sur un code de diffusion entre états localisés qui nous a permis de mieux appréhender le transport dans ces structures. Un important travail de développement de l'outil de simulation a été nécessaire. Ce code a révélé le rôle déterminant du profil de dopage sur le niveau de courant d'obscurité. Nous avons ainsi pu réaliser de nouvelles structures aux profils de dopage optimisés et dont le niveau de courant d'obscurité est abaissé de 50%. Nous avons par ailleurs pu apporter une interprétation quantique à la forme des courbes I(V) observée. Mais notre code de simulation s'avère plus généralement un outil puissant de simulation du transport dans les hétérostructures. L'influence des défauts de croissance (défauts d'interface et désordre) a pu être quantifiée et nous avons pu apporter les premières prédictions de performances de QCD THz. Enfin l'influence des effets non locaux sur le transport a été étudiée. L'observation de dents de scie sur les courbes I(V) de QWIP a pu être modélisée et son influence sur la détectivité évaluée.

Quantum well infrared photodetectors (QWIP) utilize quantum wells of large bandgap materials to detect infrared radiation. When compared to conventional low bandgap LWIR photodetectors, the QWIP technology offers largest format thermal imagers with much better uniformity. The theoretical part of this study includes the development of a QWIP ensemble Monte Carlo simulator. Capture paths of electrons to quantum wells are simulated in detail. For standard AlGaAs/GaAs QWIPs, at medium and high E-fields L valley quantum well (QW) is a trap for electrons which causes higher capture probability when compared with InP/InGaAs and GaAs/InGaAs QWIPs. The results suggest that high photoconductive gain observed in InP/InGaAs and GaAs/InGaAs QWIPs is not due to good transport properties of binary barrier material but due to higher &amp / #61511 / -L valley energy separation. The experimental part of the study includes the fabrication and characterization of InP/InGaAs and InP/InGaAsP QWIPs and 640x512 FPAs with the main objective of investigating the feasibility of these material systems for QWIPs. The InP/InGaAs and InP/InGaAsP QWIP detectors showed specific detectivity values above 1x1010 cm.Hz1/2/W (70K, f/2, background limited). The devices offer higher allowable system noise floor when compared with the standard AlGaAs/GaAs QWIP technology. It is also experimentally shown that for strategic applications LWIR InP based QWIPs have advantages over the standard QWIP technology. The InP/InGaAs 640x512 QWIP FPA reached 36 mK average NETD value at 70 K with f/1.5 optics and 10 ms integration time. The InP/InGaAsP QWIP on the other hand yielded 38 mK NETD histogram peak at 70 K with f/1.5 optics and 5 ms integration time on 320x256 window of the 640x512 FPA.

Excellent uniformity and mature material properties of Quantum Well Infrared Photodetectors (QWIPs) have allowed the realization of large format, low cost staring focal plane arrays (FPAs) in various thermal imaging bands. AlGaAs/InGaAs and AlGaAs/GaAs materials systems have been the standard systems for the construction of mid-wavelength infrared (MWIR) and long-wavelength (LWIR) QWIPs. However AlGaAs/GaAs QWIP FPAs suffer from low quantum and conversion efficiencies under high frame rate (low integration time) and/or low background conditions limiting the application area of standard QWIPs. This thesis focuses on the growth and development of InP based single and dual band QWIP FPAs. We experimentally demonstrate that QWIPs on InP substrates provide important advantages that can be utilized to overcome the bottlenecks of the standard GaAs based QWIP technology. InP/InGaAs material system is an alternative to AlGaAs/GaAs for LWIR QWIPs. We demonstrate a large format (640x512) LWIR QWIP FPA constructed with strained InP/InGaAs material system. The strain introduced to the structure shifts the cut-off wavelength from ~8.5 to 9.7 &micro / m with lambdap=8.9 &micro / m. The FPA fabricated with the 40-well epilayer structure yielded a peak quantum efficiency as high as 12% with a broad spectral response (&amp / #8710 / lambda/lambdap=17%). The peak responsivity of the FPA pixels is larger than 1.4 A/W with conversion efficiency as high as 20% in the bias region where the detectivity is reasonably high (2.6x1010 cmHz1/2/W, f/1.5, 65 K). The FPA providing a background limited performance temperature higher than 65 K (f/1.5) satisfies the requirements of most low integration time/low background applications where AlGaAs/GaAs QWIPs cannot be utilized due to low conversion efficiency and read-out circuit noise limited sensitivity. Noise equivalent temperature differences (NETD) of the FPA are as low as 19 and 40 mK with integration times as short as 1.8 ms and 430 &micro / s (f/1.5, 65 K), respectively. We also experimentally demonstrate that the cut-off wavelength of MWIR AlInAs/InGaAs QWIPs can be tuned in a sufficiently large range in the MWIR atmospheric window by only changing the quantum well (QW) width at the lattice matched composition. The cut-off wavelength can be shifted up to ~5.0 &micro / m with a QW width of 22 &Aring / in which case very broad spectral response (&amp / #8710 / lambda/lambdap=~30%) and a reasonably high peak detectivity is achievable leading to a NETD as low as 14 mK (f/2) with 25 &micro / m pitch in a 640x512 FPA. The advantages of InP based MWIR and LWIR single band QWIPs were combined by growing and fabricating a mid format (320x256) dual band QWIP FPA. The FPA provided NETD (f/1.5, 65 K, 19 ms) values of 27 mK and 29 mK in the MWIR and LWIR modes with an impressively low DC signal nonuniformity of ~ 4%. The results clearly demonstrate that InP based material systems display high potential for MWIR and LWIR single band and MWIR/LWIR dual band QWIP FPAs needed by third generation thermal imagers by overcoming the limitations of the standard GaAs based QWIPs under high frame rate (low integration time) and/or low background conditions.

InAsxSb1-x (Indium Arsenide Antimonide) is an important low bandgap semiconductor whose high quality growth on GaAs or Si substrates is indispensible for low cost, large format infrared focal plane arrays (FPAs). Quantum well infrared photodetector (QWIP) technology, relying on mature semiconductors, is also promising for the above purpose. While AlGaAs/GaAs has been the standard material system for QWIPs, the search for alternative materials is needed for better performance. This thesis reports a detailed investigation of molecular beam epitaxy grown mid-wavelength infrared InAsxSb1-x photodiodes on alternative substrates, and long wavelength infrared InP/InGaAs QWIPs. In the first part of the study, InSb and InAs0.8Sb0.2 photodiodes grown on Si and GaAs substrates are investigated to reveal the performance degrading mechanisms due to large lattice mismatch. InAs0.8Sb0.2/GaAs photodiodes yield peak detectivities of 1.4&times / 1010 and 7.5&times / 108 cmHz&frac12 / /W at 77 K and 240 K, respectively, showing that the alloy is promising for both cooled and near room temperature detectors. Under moderate reverse bias, 80 K RoA product limiting mechanism is trap assisted tunneling, which introduces considerable 1/f noise. InSb/Si photodiodes display peak 77 K detectivity as high as ~1&times / 1010 cmHz 1/2/W and reasonably high peak quantum efficiency in spite of large lattice mismatch. RoA product of detectors at 80 K is limited by Ohmic leakage with small activation energy (25 meV). Bias and temperature dependence of 1/f noise is in reasonable agreement with Kleinpenning&rsquo / s mobility fluctuation model, confirming the validity of this approach. The second part of the study concentrates on InP/In0.53Ga0.47As QWIPs, and 640&times / 512 FPA, which to our knowledge, is the largest format InP/InGaAs QWIP FPA reported. InP/InGaAs QWIPs yield quantum efficiency-gain product as high as 0.46 under moderate bias. At 70 K, detector performance is background limited with f/2 aperture up to ~3 V bias where peak responsivity (2.9 A/W) is thirty times higher than that of the Al0.275Ga0.725As/GaAs QWIP with similar spectral response. Impact ionization in InP/InGaAs QWIPs does not start until the average electric-field reaches 25 kV/cm, maintaining high detectivity under moderate bias. The 640&times / 512 InP/InGaAs QWIP FPA yields noise equivalent temperature difference of ~40 mK at an FPA temperature as high as 77 K and reasonably low NETD even with short integration times (t). 70 K NETD values of the FPA with f/1.5 optics are 36 and 64 mK under &ndash / 0.5 V (t=11 ms) and &ndash / 2 V (t=650 Rs) bias, respectively. The results clearly show the potential of InP/InGaAs QWIPs for thermal imaging applications requiring short integration times. Keywords: Cooled infrared detectors, InAsSb, QWIP, focal plane array.

A wide range of applications have been recognized for terahertz radiations. In fact, medical imaging, homeland security screening, very high-speed wireless telecommunications systems and even drug and gas detection are boosting the development of terahertz emitters and receivers. The work of this thesis is among the efforts in that regard. Actual terahertz detectors are suffering many drawbacks, they are bulky, very slow, not very sensitive or operates at non-practical temperatures. Combined with the complexity to realize terahertz emitters, it explains the difficulties of terahertz radiations to ensure market penetration with practicable civil applications. In that regard, we aim to better understand and improve a specific terahertz photodetector: the Terahertz Quantum Well Photodetector. Those devices working principle relies on a photocurrent created by the excitation of electrons from ground states of quantum wells to the continuum under terahertz impinging light. The intensity of the photocurrent is depending on the intensity of the radiation received by the device. The device active region is made of a multiple quantum wells GaAs/AlGaAs system. By changing the design of the device, that is the thicknesses of each layer, the aluminum fraction of the doping concentration, we can modify its performances. Documented and commented Matlab functions and routines have been implemented in order to simulate a given structure and scripts have been written to find the optimum parameters for a target absorption frequency. Our model has been verified by comparison with experimental data reported in the literature. Based on our model, we systematically study the impact of the active region and contact parameters on the device performances. In addition, innovative designs are proposed in order to reduce the undesirable dark current and thus increase the detectivity. They benefits from many-body effects, effects that are usually a constraint on the design. To our knowledge this is the first time those effects are used to realize innovative designs and increase the performances of quantum well infrared photodetectors. Finally we expose other designs that have been tested in the infrared domain with QWIP and adapt them to the terahertz range. In particular, we propose a quantum cascade photodetector, a double barrier bound-to-miniband and a phonon-assisted band to miniband structures.