L'énergie solaire est une source d'énergie renouvenable, peu polluante, disponible universellement et abondante. Elle est donc une solution de choix pour résoudre les problèmes énergétiques et environnementaux de l'humanité. Cependant, les panneaux solaires couramment utilisés pour transformer l'énergie solaire en électricité sont encore trop dispendieux pour une utilisation répandue. L'utilisation de lumière concentrée se veut une méthode de réduire les coûts de l'électricité produite, mais cette réduction n'est pas encore atteinte. Ce projet propose d'explorer des matériaux et des structures semiconductrices fabriqués par épitaxie par jets chimiques qui pourraient être utilisés dans des cellules solaires optimisées pour la très haute concentration. En premier lieu, plusieurs designs de cellules solaires sont simulés avec une approche multiphysique pour identifier des structures permettant de minimiser les coûts de l'électricité à travers une maximisation du facteur de concentration. Basé sur ces structures de cellules solaires, plusieurs designs de jonctions tunnels sont simulés et une jonction tunnel standard (GaAs:Te/AlGaAs:C) est choisie. Le GaAs dopé au Te présente un problème de morphologie de surface à haut dopage. Ce problème est étudié et éliminé à travers l'optimisation des conditions de croissance. Dans le cas de l'AlGaAs dopé au C, le niveau de dopage est maximisé à travers l'utilisation d'un précurseur chimique qui n'est pas utilisé en CBE, le TMA. Suite à l'optimisation de ces deux matériaux, des jonctions tunnels avec d'excellentes performances sont crûes. Par la suite, une tentative de croissance de jonction tunnel GaInP/AlGaAs avec des boîtes quantiques en InAs permet d'améliorer le courant tunnel par rapport à une jonction tunnel sans boîtes, mais sans atteindre des performances satisfaisantes pour l'inclusion dans une cellule solaire. Ensuite, un matériau alternatif pouvant servir de jonction p-n dans les structures de cellules solaires, le GaInAsP, est caractérisé par photoluminescence pour explorer l'effet des paramètres de croissance sur la séparation de phase et l'influence de cette séparation sur les propriétés du matériau. On en découvre qu'une forte séparation de phase induit la présence d'états localisés sous le bandgap qui affecterait les performances d'une cellule solaire. Ensuite, il est démontré que le dopage de type n idéal est le Te alors que celui de type p est au Zn. Cependant, les temps de vie obtenus pour le GaInAsP dopé n ou p sont très bas et donneraient de mauvaises performances de cellules solaires. Ces temps de vie sont néamoins meilleurs que ceux obtenus pour l'AlGaAs, l'alternative au GaInAsP.

Neste trabalho, apresentamos os resultados de estudos com poços quânticos parabólicos (PQW, Parabolic Quantum Well ) de AlGaAs crescidos sobre substratos de GaAs pela técnica de epitaxia por feixe molecular. Medidas de transporte em PQWs do tipo n e do tipo p com larguras de 1000 ºA ate 4000 ºA em baixas temperaturas indicam um aumento abrupto do coeficiente Hall para um campo magnético critico de aproximadamente 3 T. Nosso estudo concentra-se na interpretação deste aumento observado. Com este propósito, estudamos através de cálculos autoconsistentes e de aproximações anal¶³ticas o processo de transferência de cargas em amostras com PQWs. Determinamos as densidades superficiais de cargas ns e ps, e comparamos estes resultados com os obtidos experimentalmente. Verificamos que os melhores resultados para a densidade de cargas (ns) s~ao aqueles determinados pelos cálculos autoconsistentes. No entanto, as aproximações analíticas se mostram importantes para descrever de forma qualitativa os resultados experimentais para amostras do tipo p. Numa segunda parte do nosso trabalho, estudamos a influencia da aplicação de campos magnéticos ao longo da direção de crescimento nas amostras com PQWs. Observamos uma diminuição na largura de densidade de cargas n(z) e do potencial total V (z). Estes resultados em combinação com o processo de transferência de cargas, levam a uma diminuição da densidade de portadores no poço, produto da redistribuição das cargas entre o poço e as camadas com dopagem de silencio. Desta forma, atribuímos o aumento no coeficiente Hall como sendo oriundo de uma diminuição da densidade de cargas dentro do PQW. / We present the results of experiments and calculations done on AlGaAs Parabolic Quantum Wells (PQWs) grown on GaAs by molecular beam epitaxial tecniques. Transport measurements in n-type and p-type samples with widths between 1000 ºA and 4000 ºA at low temperatures indicate an abrupt increase of the Hall coeficient at a critical field B ¼ 3 T. Our study focuses on the interpretation of this observed increase. To this end, we study by means of self-consistent numerical simulations and analytical approximations the charge transfer process in PQWs. We compare our results for the sheet densities with those observed experimentally. The best results are obtained for n-type samples for which we could numerical simulations. However, the analytical expressions we obtained also describe qualitatively the experimental results, and can be applied to p-type samples. In the second part of this work we study the efect of a magnetic feld applied perpendicular to the well. The simulations indicate a diminishing of the charge density and the total potential in the well. These results, combined with the charge transfer process, lead to a redistribution of charge between the well and the dopant layers. Therefore, we interpret the observed increase of the Hall coefcient as the result of a depletion of charge in the parabolic quantum well.

A research synopsis is presented summarizing work with integration of Ge and III-V semiconductors and optical devices with Si. III-V GaAs/AlGaAs quantum well lasers and GaAs/AlGaAs optical circuit structures have been fabricated on Si using Ge/GeSi/Si virtual substrates. The lasers fabricated on bulk GaAs showed similar output characteristics as those on Si. The GaAs/AlGaAs lasers fabricated on Si emitted at 858nm and had room temperature cw lifetimes of ~4hours. Straight optical links integrating an LED emitter, waveguide and detector exhibited losses of approximately 144dB/cm. A process for fabrication of a novel CMOS-compatible platform that integrates III-V or Ge layers with Si is demonstrated. Thin Ge layers have been transferred from Ge/GeSi/Si virtual substrates to bulk Si utilizing wafer bonding and an epitaxial Si CMP layer to facilitate virtual substrate planarization. A unique CMP-less method for removal of Ge exfoliation damage induced by the SmartCut™ process is also presented. / Singapore-MIT Alliance (SMA)

The work presented here report findings in (1) infrared detectors based on p-GaAs/AlGaAs heterojunctions, (2) J and H aggregate sensitized heterojunctions for solar cell and photon detection applications, (3) heterojunctions sensitized with quantum dots as low cost solar energy conversion devices and near infrared photodetectors. (1)A GaAs/AlGaAs based structure with a graded AlGaAs barrier is found to demonstrate a photovoltaic responsivity of ~ 30mA/W (~ 450mV/W) at the wavelength of 1.8 mm at 300K. Additionally the graded barrier has enhanced the photoconductive response at 78 K, showing a responsivity of ~ 80mA/W with a D*=1.4×108 Jones under 1V bias at 2.7 mm wavelength. This is an approximately 25 times improvement compared to the flat barrier detector structure, probably due to the improved carrier transport, and low recapture rate in the graded barrier structure. However, these graded barrier devices did not indicate a photoresponse with photoconductive mode at 300K due to high shot noise. Additionally, two generation-recombination noise components and a 1/f noise component were identified. A series of GaAs/AlGaAs multilayer hetero-junction structures were tested as thermal detectors. A superlattice structure containing 57% Al fraction in the barrier and 3 × 1018 cm-3 p-doped GaAs emitter showed the highest responsivity as a thermal detector with a TCR of ~ 4% K-1, at 300K. (2)The photovoltaic properties of heterojunctions with J-/ H- aggregated dye films sandwiched between n– and p-type semiconductors were investigated for potential application as solar cells and IR detectors. Films of cationic dye Rhodamine-B-thiocyanate adsorbed on Cu2O substrate are found to form organized dye layers by self-assembled J- aggregation, resulting in large red-shifts in the photo -response. Additionally, cells sensitized with a pentamethine cyanine dye exhibited a broad spectral response originating from J- and H-aggregates. The photocurrent is produced by exciton transport over relatively long distances with significant hole-mobility as well as direct sensitized injection at the first interface. (3) A ZnO/PbS-QD/Dye heterostructure had enhanced efficiency compared to ZnO/Dye heterostructure as a solar cell. Furthermore, a ZnO/PbS-QD structure has demonstrated UV and NIR responses with 4×105V/W (390 nm) and 5.5×105 V/W (750 nm) under 1V bias at 300K.

Neste trabalho, apresentamos os resultados de estudos com poços quânticos parabólicos (PQW, Parabolic Quantum Well ) de AlGaAs crescidos sobre substratos de GaAs pela técnica de epitaxia por feixe molecular. Medidas de transporte em PQWs do tipo n e do tipo p com larguras de 1000 ºA ate 4000 ºA em baixas temperaturas indicam um aumento abrupto do coeficiente Hall para um campo magnético critico de aproximadamente 3 T. Nosso estudo concentra-se na interpretação deste aumento observado. Com este propósito, estudamos através de cálculos autoconsistentes e de aproximações anal¶³ticas o processo de transferência de cargas em amostras com PQWs. Determinamos as densidades superficiais de cargas ns e ps, e comparamos estes resultados com os obtidos experimentalmente. Verificamos que os melhores resultados para a densidade de cargas (ns) s~ao aqueles determinados pelos cálculos autoconsistentes. No entanto, as aproximações analíticas se mostram importantes para descrever de forma qualitativa os resultados experimentais para amostras do tipo p. Numa segunda parte do nosso trabalho, estudamos a influencia da aplicação de campos magnéticos ao longo da direção de crescimento nas amostras com PQWs. Observamos uma diminuição na largura de densidade de cargas n(z) e do potencial total V (z). Estes resultados em combinação com o processo de transferência de cargas, levam a uma diminuição da densidade de portadores no poço, produto da redistribuição das cargas entre o poço e as camadas com dopagem de silencio. Desta forma, atribuímos o aumento no coeficiente Hall como sendo oriundo de uma diminuição da densidade de cargas dentro do PQW. / We present the results of experiments and calculations done on AlGaAs Parabolic Quantum Wells (PQWs) grown on GaAs by molecular beam epitaxial tecniques. Transport measurements in n-type and p-type samples with widths between 1000 ºA and 4000 ºA at low temperatures indicate an abrupt increase of the Hall coeficient at a critical field B ¼ 3 T. Our study focuses on the interpretation of this observed increase. To this end, we study by means of self-consistent numerical simulations and analytical approximations the charge transfer process in PQWs. We compare our results for the sheet densities with those observed experimentally. The best results are obtained for n-type samples for which we could numerical simulations. However, the analytical expressions we obtained also describe qualitatively the experimental results, and can be applied to p-type samples. In the second part of this work we study the efect of a magnetic feld applied perpendicular to the well. The simulations indicate a diminishing of the charge density and the total potential in the well. These results, combined with the charge transfer process, lead to a redistribution of charge between the well and the dopant layers. Therefore, we interpret the observed increase of the Hall coefcient as the result of a depletion of charge in the parabolic quantum well.

Le but de cette thèse a été de caractériser des boîtes quantiques obtenues avec une nouvelle méthode de croissance. Utilisant des techniques de microphotoluminescence, nous avons étudié les différentes contributions au mélange des bandes de trous lourds et de trous légers. En l'absence de contrainte, la distribution du paramètre de mélange est plus homogène ; cependant, d'autres contributions deviennent dominantes et nous les avons discutées. Nous avons mesuré les paramètres magnéto-optiques : facteurs Landé de l'électron et du trou, décalage diamagnétique, paramètres de structure fine des états noirs et brillants. Les valeurs obtenues ont permis d'estimer la variation des paramètres géométriques des boîtes, ce qui est lié à la qualité du contrôle de la croissance. La polarisation des états noirs mesurée s'est révélée différente de celle prévue selon le modèle utilisé précédemment dans la littérature. Utilisant un modèle théorique récent, nous avons reproduit nos observations, ce qui met en évidence une modulation possible de la polarisation des états noirs par le champ magnétique. Finalement, nous avons effectué des études de contrôle de charges dans des structures n-i Schottky. Pour des boîtes uniques, des états multichargés ont été observés. Nous avons mesuré les énergies de liaison des trions positif et négatif, au préalable à une étude sur des molécules de boîtes. Nous avons observé des anticroisements des états S des trous dans deux boîtes, en accord avec nos prévisions basées sur les paramètres nominaux de l'échantillon. / The goal of this thesis work was to characterise quantum dots obtained by a novel growth method. We used microphotoluminescence techniques to study multiple properties of these dots. We have evaluated main contributions to light-heavy hole valence band mixing. Contrary to self-assembled dots, we find a more homogeneous distribution of the mixing parameter, which can be explained by the absence of mechanical tension due to lattice mismatch. We have also measured magneto-optical parameters such as electron and hole g-factors, diamagnetic shift, fine structure splitting for bright and dark states. These results allowed us to estimate geometric parameters of dots, making a point on the growth quality. Polarisation studies on the dark states have revealed a result different from previous theoretical predictions. We have used a recently presented model to explain our findings. The last part of this work presents results on quantum dots embedded in an n-i Schottky structure. We have measured binding energies of positive and negative trions, to make a connection with previous results, to then study double quantum dot system. We have observed an anticrossing of hole S states, which is in agreement with our estimations based on sample parameters.

Exziton-Polaritonen (Polaritonen), hybride Quasiteilchen, die durch die starke Kopplung von Quantenfilm-Exzitonen mit Kavitätsphotonen entstehen, stellen auf Grund ihrer vielseitigen und kontrollierbaren Eigenschaften einen vielversprechenden Kandidaten für die Entwicklung einer neuen Generation von nichtlinearen und integrierten elektrooptischen Bauteilen dar. Die vorliegende Arbeit beschäftigt sich mit der Entwicklung und Untersuchung kompakter elektrooptischer Bauelemente auf der Basis von Exziton-Polaritonen in Halbleitermikrokavitäten. Als erstes wird die Implementierung einer elektrisch angeregten, oberflächenemittierenden Polariton-Laserdiode vorgestellt, die ohne ein externes Magnetfeld arbeiten kann. Dafür wird der Schichtaufbau, der Q-Faktor, das Dotierprofil und die RabiAufspaltung der Polariton-Laserdiode optimiert. Der Q-Faktor des finalen Aufbaus beläuft sich auf Q ~ 16.000, während die Rabi-Aufspaltung im Bereich von ~ 11,0 meV liegt. Darauf aufbauend werden Signaturen der Polariton-Kondensation unter elektrischer Anregung, wie ein nichtlinearer Anstieg der Intensität, die Reduktion der Linienbreite und eine fortgesetzte Verschiebung der Emission zu höheren Energien oberhalb der ersten Schwelle, demonstriert. Ferner werden die Kohärenzeigenschaften des Polariton-Kondensats mittels Interferenzspektroskopie untersucht. Basierend auf den optimierten Halbleiter-Mikroresonatoren wird eine Kontaktplattform für die elektrische Anregung ein- und zweidimensionaler Gitterstrukturen entwickelt. Dazu wird die Bandstrukturbildung eines Quadrat- und Graphen-Gitters unter elektrischer Anregung im linearen Regime untersucht und mit den Ergebnissen der optischen Charakterisierung verglichen. Die erhaltenen Dispersionen lassen sich durch das zugehörige Tight-Binding-Modell beschreiben. Ferner wird auch eine elektrisch induzierte Nichtlinearität in der Emission demonstriert. Die untersuchte Laser-Mode liegt auf der Höhe des unteren Flachbandes und an der Position der Γ-Punkte in der zweiten Brillouin-Zone. Die zugehörige Modenstruktur weist die erwartete Kagome-Symmetrie auf. Abschließend wird die Bandstrukturbildung eines SSH-Gitters mit eingebautem Defekt unter elektrischer Anregung untersucht und einige Eigenschaften des topologisch geschützten Defektzustandes gezeigt. Dazu gehört vor allem die Ausbildung der lokalisierten Defektmode in der Mitte der S-Bandlücke. Die erhaltenen Ergebnisse stellen einen wichtigen Schritt in der Realisierung eines elektrisch betriebenen topologischen Polariton-Lasers dar. Abschließend wird ein elektrooptisches Bauteil auf der Basis von Polaritonen in einem Mikrodrahtresonator vorgestellt, in dem sich die Propagation eines PolaritonKondensats mittels eines elektrostatischen Feldes kontrollieren lässt. Das Funktionsprinzip des Polariton-Schalters beruht auf der Kombination einer elektrostatischen Potentialsenke unterhalb des Kontaktes und der damit verbundenen erhöhten ExzitonIonisationsrate. Der Schaltvorgang wird sowohl qualitativ als auch quantitativ analysiert und die Erhaltenen Ergebnisse durch die Modellierung des Systems über die GrossPitaevskii-Gleichung beschrieben. Zusätzlich wird ein negativer differentieller Widerstand und ein bistabiles Verhalten in der Strom-Spannungs-Charakteristik in Abhängigkeit von der Ladungsträgerdichte im Kontaktbereich beobachtet. Dieses Verhalten wird auf gegenseitig konkurrierende Kondensats-Zustände innerhalb der Potentialsenke und deren Besetzung und damit direkt auf den räumlichen Freiheitsgrad der PolaritonZustände zurückgeführt. / Exciton-polaritons (polaritons), hybrid quasi-particles formed by the strong coupling between quantum well excitons and microcavity photons, are promising candidates for the realization of a new generation of nonlinear and integrated electrooptical devices. Compared to photonic or electrical approaches distinguishing advantages of Polaritons are their versatile and tuneable properties that allow electrical excitation and easy manipulation, which is both advantageous for on-chip applications. The present thesis deals with the development, implementation, and improvement of compact electrooptical devices based on exciton-polaritons in semiconductor microcavities. At first the implementation of an electrically driven vertically emitting polariton laser diode, which operates without the need of an applied magnetic field, is presented. For this purpose, the layer structure, quality factor, doping profile and Rabi-splitting of the polariton laser diode is optimized. The final design consists of a high-quality factor Al0.20Ga0.80As/AlAs microcavity (Q ~ 16,000) and features a Rabi-splitting of ~ 11.0 meV. Signatures for polariton condensation under electrical excitation are shown in the processed device. It features a clear nonlinearity in its input-output characteristic, a well-pronounced drop in the emission linewidth and a persisting blueshift above the first threshold with increasing pump-power. On top of that, evidence of the systems coherence properties in the condensed phase is provided directly by utilizing interference spectroscopy. Based on the optimized microcavity structures a process for the electrical excitation of one- and two-dimensional potential landscapes is developed. At first, the linear band structures of polaritonic square as well as honeycomb lattices are studied under electrical injection and compared to the results acquired by optical excitation. The obtained dispersions are reproduced by a tight-binding model. Moreover, the capability of the device to facilitate an electrically induced nonlinear emission is demonstrated. The investigated laser mode at the high symmetry Γ points in the second Brillouin zone, is located at the low energy flatband, as verified by the kagome geometry of the measured mode structure. Subsequent, the results of a one-dimensional SSH chain are presented under electrical excitation. In addition, the properties of a built-in lattice defect, forming a topological protected state in the middle of the S band gap, are investigated, paving the way towards the realization of electrically driven topological polariton lasers. Finally, an electrooptical polariton switch is demonstrated as a prototype of a polaritonic field-effect transistor. Here, an optical generated polariton condensate propagating along a one-dimensional channel is controlled by an electrical gate. The operation of the device relies on the combination of an electrostatic potential trap underneath the contact, and the associated exciton ionization. The switching behaviour is analysed in a qualitative as well as in a quantitative manner and verified by modelling the experimental findings with the Gross-Pitaevskii equation. Furthermore, a pronounced negative differential resistance and a strong bistability is observed in the photocurrent response as a function of the carrier density. This is attributed to competing transitions of trapped condensate modes and thus directly to the spatial degree of freedom of the polariton states, which represents a completely new way to create bistability.

No description available.

GaP ist ein Halbleiter mit einer großen Bandlückenenergie und infolgedessen transparent im größten Teil der sichtbaren Wellenlängen. GaP hat außerdem die kleinste Gitterfehlanpasung zu Si (weniger als 0.4%). Das macht GaP ein interessantes Material für monolithische Integration zu III–V Lichtsender auf Si. Diese Arbeit ist eine Untersuchung über die strukturellen und optische Eigenschaften von (Al, Ga) (As, P) Heterostrukturen auf GaP (001) -Substrat aufgewachsen. Die Einflüsse des PH3 Fluss und Wachstumstemperatur untersucht auf dem Kristallqualität und Oberflächenqualität von AlGaP/GaP Heterostructure. Experimentelle Ergebnisse deuten darauf hin, dass eine Wachstumstemperatur von 490 oC und ein geknackter (engl. cracked) PH3 Fluss von 2.7 sccm zur besten AlGaP Qualität und gleichzeitig zur guten GaP Qualität führen. Um die ineffiziente Lichtemission von GaP zu überwinden wurde GaAs in der GaP-Matrix gewachsen. Die Entstehung der Quantenpunkte wurde durch die 3.7% Gitterfehlanpassung zwischen GaAs und GaP für GaAs Nenndicke über 1,2 ML. Die optischen Messungen zeigen zwei Peaks im Bereich von 1,7 bis 2,1 eV und die Lumineszenz auf Raumtemperatur für 2,7 und 3,6 ML-Proben. Die hohe Energieemission wird der indirekten Rekombination in den dünnen Quantentröge oder kleine gespannte Quantenpunkte zurückzuführen, Während die niedrige Energie Emission ist aufgrund der direkten Elektron-Loch- Rekombination in der entspannten Quantenpunkte. Die Wirkung von Al wird untersucht auf die energetische Bandausrichtung und auf die elektronische Struktur der (Al,Ga)As Quantenstrukturen. Die optische Spektren zeigten einen blaue Verschiebung (engl. blue shift) mit wachsendem Al-Inhalt und die höchste missionsenergie für die (Al,Ga)As/GaP- Heterostruktur war 2.17 eV die zum indirekten Typ-II-Rekombination zusammenhängt. / Transparency of GaP due to the large indirect bandgap energy and its small lattice mismatch with Si make GaP an interesting candidate for optoelectronic devices in visible wavelength. This thesis is an investigation on the structural and optical characteristics of (Al,Ga)(As,P) heterostructures grown on GaP (001) substrates. The influences of the PH3 flux and growth temperature are studied on the crystal and surface quality of AlGaP/GaP heterostructure. The results indicate the narrow growth window of PH3 = 2.7 sccm and growth temperature = 490oC as the optimized conditions. To overcome the inefficient light emission of indirect GaP, direct bandgap GaAs was grown as the quantum structures in the GaP matrix. The QD formation is driven by the 3.7% lattice mismatch between GaAs and GaP for GaAs nominal thickness above 1.2 ML. The optical measurements show two peaks in the range of 1.7 to 2.1 eV and the luminescence up to room temperature for 2.7 and 3.6 ML samples. The high energy emission is attributed to indirect carrier recombination in the thin quantum wells or small strained quantum dots, whereas the low energy red emission is due to the direct electron-hole recombination in the relaxed quantum dots. The influence of the Al content on the band alignment and electronic structure of (Al,Ga)As quantum structures is studied. The optical spectra illustrate the blueshift of the radiative emission with increasing the Al content and the highest emission energy of 2.17 eV is observed for the (Al,Ga)As/GaP system that is related to the indirect type-II radiative recombination.

Neste trabalho, apresentamos o resultado de nossas investigações em amostras de poços quânticos parabólicos (PQW) de AlGaAs crescidas em substratos de GaAs por MBE (Molecular Beam Epitaxy). Nossos estudos se concentram nas implicações da variação do fator g de Landé ao longo da estrutura dos PQW, a qual ocorre em virtude da dependência dessa grandeza com respeito ao conteúdo de Al na liga AlGaAs. Essas implicações são analisadas através de medidas de transporte eletrônico (medidas de Hall e do efeito Shubnikov-de Haas). As medidas de Subnikov-de Haas a temperaturas da ordem de dezenas a centenas de milikelvin com variação do ângulo de inclinação se mostram um eficiente método para a determinação do fator g. Distinguimos não só o fator g determinado pelas propriedades da liga, como também uma contribuição oriunda de efeitos de muitos corpos (contribuição de troca). Por outro lado, as medidas de Hall nos revelam um comportamento anômalo, que mostramos não ter origem no conhecido "efeito Hall anômalo" presente em materiais ferromagnéticos, nem em efeitos de ocupação de múltiplas sub-bandas. Atribuímos o fenômeno a um efeito "válvula de spin", conseqüente da variação espacial do fator g. Nossas observações nos permitem a idealização de um transistor "válvula de spin", prescindindo do emprego de materiais magnéticos. / We present the results of our investigations concerning MBE grown AlGaAs/GaAs parabolic quantum well (PQW) samples. We focused on the variation of the Landé g factor along the structure of the PQWs, which occur as a consquence of its dependence on the Al content on the alloy AlGaAs. The implications are studied by Hall and Shubnikov-de Haas measurements. Shubnikov-de Haas measurements at temperatures of the order of tenths to hundreds of milikelvin with variation of the tilt angle are shown to be an efficient method for the determination of the g factor. We could distinguish not only the alloy g factor, but its many body contribution (exchange contribution). On the other hand, Hall measurements exhibit an unusual behavior, which we prooved it has no relation neither to the well known "anomalous Hall effect", a characteristic of ferromagnetic materials, nor to a multi subband occupation effect. We atribute such behavior to a "spin valve effect", caused by the spatial variation of the g factor. Our observations allow us to idealize a "spin valve" transistor, without any ferromagnetic material in its structure.