We have studied the electronic properties of InGaAs/AlInAs nano wire by using Shubnikov-de Hass (SdH)measurement at 0.3K.In order to study the effect of the channel width on the 2DEG,we made the nanometer-scaled 2DEG channels varied with different widths from 700 nm to 1400 nm by focus ion beam. On the AlGaAs/AlInAs nanowires we have studied I-V characteristics with gate-voltage and observed the work range from -3 V to 3 V. After illuminating at 0.3 K, the carrier density of the sample InGaAs-1400 nm increased and observed the persistent photoconductivity effect. After SdH measurement at 0.3 K, we found saturation current of these samples at 77 K but did not observe change with different gate voltage.

Aggressive downscaling of complementary metal-oxide-semiconductor (CMOS) transistors has pushed Si-based transistors to their limit. III-V materials have much higher electron mobility compared to Si, which can potentially provide better device performance. Therefore, III-V semiconductor materials have been actively investigated as alternative channel materials, which can extend Moore’s law on CMOS scaling beyond the 22 nm node not only by relying on scaling. Meanwhile, conventional silicon dioxide cannot easily meet the requirement for the scaling of the equivalent oxide thickness; as a result, various high dielectric constant (high-k) materials have been incorporated onto the III-V semiconductor substrate. Nevertheless, the key challenges for high-k/III-V MOSFETs still need to be solved in order to implement high performance high-k/III-V MOSFETs. Those challenges are the lack of high quality and thermodynamically stable insulators that passivate the gate dielectric/III-V interface, compatible III-V p-type MOSFETs, and reliability issue of III-V MOSFETs, etc. The main focus of this dissertation is to develop proper fabrication processes and structures for III-V MOSFETs devices that result in good interface quality and high device performance. Firstly, we studied the effect of interfacial chemistry on ZrO2/InGaAs gate stack comprehensively, comparing ALD ZrO2 with H2O vs. O3 as the oxidizer. We found that the amount of oxygen is critical to form a good interface. Excessive oxygen concentration, e. g. using O3 as the ALD precursor, induces III-V native oxides at the interface. The second part of this dissertation focuses on the III-V MOSFETs with various IPLs. Various IPLs have been demonstrated, for example, a thin PVD Si IPL, and ALD Al2O3, HfAlOx, and ZrAlOx. Those IPLs are demonstrated to be effective interfacial dielectric layers to improve device performance, including frequency dispersion, SS, Ion, effective channel mobility, and reliability. The third part of this study highlights a novel CF4 post-gate plasma treatment on III-V MOSFETs. Fluorine incorporation was demonstrated on various high-k/III-V gate stacks and achieved significant improvements, including Al2O3/In0.53Ga0.47As, Al2O3/InP, HfO2/In0.53Ga0.47As, and HfO2/InP. Detailed physical analysis, electrical characterization and device performance were carried out. With F incorporation, we have successfully developed excellent interface quality of high-k/III-V MOSFETs. As a result, high-performance III-V MOSFETs have been realized. Finally, emerging non-volatile memories, RRAMs, have been demonstrated. We addressed its conducting mechanism by conducting various experiments and purposed a model for SiOx RRAMs: the conducting filament is randomly formed within the SiOx at the sidewall edge, depending on pre-existing defects. Moreover, the rupture/recovery could occur anywhere along the conducting filament, depending on a random process that determines the location of the weak spot along the conducting filament. In addition, we improved SiO2-based RRAM by incorporating a thin silicon layer onto its sidewall. This technique significantly reduced the electroforming voltage and instability of HRS current of SiO2-based RRAMs. Consequently, a tri-state pulse endurance performance over 106 cycles has been demonstrated and the data stored had good read disturb immunity and thermal disturbance. / text

Malgré les remarquables performances démontrées par les photo-détecteurs quantiques pour l'infrarouge, les progrès dans cette filière stagnent. La principale limitation est due au bruit lié à leur courant d'obscurité, qui impose, aux plus grandes longueurs d'onde, un fonctionnement à des températures cryogéniques. Ce travail de thèse a pour principal objectif de dépasser cette limite intrinsèque en combinant des structures photo-détectrices innovantes et des nano-résonateurs optiques. La réduction par plus d'un ordre de grandeur de l'épaisseur de la zone absorbante, modifie considérablement les propriétés optiques et électroniques de la structure, imposant de revisiter entièrement ses modes de fonctionnement. Dans ce contexte, ce travail de thèse vise à valider expérimentalement l'apport de la nano-photonique à l'amélioration des performances des photodiodes InGaAs.La première partie est dédiée à l'étude de photodiodes InGaAs à double hétérojonction dans le but de réduire à la fois le courant d'obscurité et l'épaisseur de la structure pour la rendre compatible à celle des nano-résonateurs optiques. La seconde partie est dévolue à la conception, la fabrication et la caractérisation de photo-détecteurs InGaAs nano-structurés de type résonateurs de mode guidé. Dans la troisième partie, les remarquables propriétés de ces photo-détecteurs sont étudiées dans un contexte de mini-matrices, premier pas vers la réalisation de caméras.Les concepts développés durant cette thèse et les résultats expérimentaux obtenus, ouvrent la voie vers une nouvelle génération de photo-détecteurs pour l'imagerie infrarouge. / Despite the outstanding performances reached by today's infrared quantum photo-detectors, progresses have been stagnating for years. The main limitation is due to the noise generated by the dark current, which requires, cooling down the devices at a cryogenic temperature for the largest wavelengths. The main objective of this thesis is to propose new concepts for overcoming these fundamental limits. By combining innovative photo-detector structures and optical nano-resonators, new structures are proposed. By reducing by more than order of magnitude the thickness of the absorbing layer, optical and electrical properties of the structure are deeply modified. As a result operating modes have to be entirely revisited. In this context, the purpose of this thesis is to characterize the behaviors, to find new compromise and to experimentally validate the nano-photonics potential to improve the performances of InGaAs photodiodes.The first part is dedicated to the study of double heterojunction InGaAs photodiodes in order to reduce both the dark current and the thickness of the structure to make it compatible with that of optical nano-resonators. The second part is devoted to the design, the fabrication and the characterization of guided mode resonant nanostructured InGaAs photo-detectors. In the third part, the remarkable properties of these photo-detectors are studied in the context of mini-arrays, the first step towards cameras realization.The concepts developed during this thesis and experimental results, pave the way to a new generation of infrared photodetector.

We have studied the electronic properties of InxGa1-xAs/ In0.52Al0.48As quantum wells by using Shubnickove-de Hass (SdH) measurement. The indium composition (x) of well layers was varied from 0.5 to 0.56 whit different structures, such as sample A is simply ¡§In0.53Ga0.47As¡¨, sample B is a step-well like¡§In0.56Ga0.44As/In0.53Ga0.47As/In0.5Ga0.47As¡¨,sample C is linearly graded well is a opposite way¡§In0.56Ga0.44As down to In0.5Ga0.5As, and sample D is linearly graded well ¡§In0.5Ga0.5As up to In0.56Ga0.44As.¡¨ It was found that the two SdH oscillations beat each other due to the population of the lowest two subbands in these samples. In order to investigate the electronic properties of the two subbands, we have done the Ven der Pauw Hall measurement . From SdH and Hall measurement, we are able to determine the individual mobility and carrier concentrations for two-subband-populated samples.

InP-based InAlAs/InGaAs pseudomorphic High Electron Mobility Transistors (pHEMTs) have shown outstanding performance; this makes them prominent in high frequency mm-wave and submillimeter-wave applications. However, conventional InGaAs/InAlAs pHEMTs have major drawbacks, i.e., very low breakdown voltage and high gate leakage current. These disadvantages degrade device performance, especially in Monolithic Microwave Integrated Circuit (MMIC) low noise amplifiers (LNAs). The optimisation of InAlAs/InGaAs epilayer structures through advanced bandgap engineering offers a key solution to the problem. Concurrently, device modelling plays a vital role in the design and analysis of pHEMT devices and circuit performance. In this research, two-dimensional (2D) physical modelling of 1 m and sub-micro metre gate length strained channel InAlAs/InGaAs/InP pHEMTs has been developed, in ATLAS Silvaco. All modelled devices were optimised and validated by experimental devices, which were fabricated at the University of Manchester. An underlying device physics insight is gained, i.e., the effect of changes to the device's physical structure, theoretical concepts and its general operation, and a reliable pHEMT model is obtained. The kink anomalies in the I-V characteristics were reproduced. The 2D simulation results demonstrate an outstanding agreement with measured DC and RF characteristics. The aim of developing linear and non-linear models for sub-micro metre transistors and their implementation in MMIC LNA design is achieved with the 0.25 m In0.7Ga0.3As/In0.52Al0.48As/InP pHEMT. An accurate method for the extraction of empirical models for the fabricated active devices has been developed, and optimised using the Advance Design System (ADS) software. The results demonstrate excellent agreement between experimental and modelled DC and RF data. Precise models for MMIC passive devices are also obtained, and incorporated in the proposed design for a single- and double-stage MMIC LNAs at C- and X-band frequencies. The single-stage LNA is designed to achieve a maximum gain ranging from 9 to 13 dB over the band of operation, while the gain is increased to between 20 dB and 26 dB for the double-stage LNA designs. A noise figure of less than 1.2 dB and 2 dB is expected, for the C- and X-band LNAs respectively, while retaining stability across all frequency bands. Although the RF performance of pHEMT is being vigorously pushed towards the terahertz (THz) region, novel devices such as the Resonant Tunnelling Diode (RTD) are needed to support future ultra-high-speed, high-frequency applications. Hence, the study of physical modelling is extended to quantum modelling of an advanced In0.8Ga0.2As/AlAs RTD device. The aim is to effectively model both large-size and submicron RTDs, using Silvaco's ATLAS software to reproduce the peak current density, peak-to-valley-current ratio (PVCR), and negative differential resistance (NDR) voltage range. The physical modelling for the RTD devices is optimised to achieve an excellent match with the fabricated RTD devices; variations in the spacer thickness, barrier thickness, quantum well thickness and doping concentration are included.

The objective of this work was to design and develop a high performance field effect transistor to be suitable for monolithic integration with a photodetector for use in long wavelength optical communication systems. It was decided that the most promising type of device for this application was a junction field effect transistor (JFET), fabricated using the alloy In.53Ga.47As grown epitaxially onto an InP substrate. The requirements for such a device were that it should have high transconductance, low input capacitance, and low gate leakage current (for high receiver sensitivity), and that it should have a structure which would be easily integrated monolithically with the desired type of photodetector - an In.53Ga.47As PIN-photodiode. Although this alloy semiconductor has favourable electron transport properties, at the start of this work, high performance field effect transistors had not been realised in this material. In particular, the In.53Ga.47AS FETs that had been made at that time were characterised by low transconductance. Using a device design that incorporated many novel and efficacious features, the JFET described in this work gave results which greatly surpassed all previous (and current) published results of similar devices. This device not only showed high performance, but the novel design features also enabled a simple fabrication scheme. Having developed this very high performance discrete device, the feasibility of monolithic integration with a In.53Ga.47As PIN-photodiode was demonstrated. Although the physical size and material requirements of these two devices were very different, novel design features enabled the construction of a monolithic PIN-FET combination, in which the performance of the JFET was not compromised.

Gas source molecular beam epitaxy (GSMBE) has been used to grow InGaAs/lnP epitaxial layers in selected areas defined by SiO2-masked InP substrates, with the goal of obtaining controlled in-plane variations in the bandgap of the InGaAs wells. The ability to alter the bandgap of the semiconductor spatially over the surface in one growth procedure is desirable for integrating laser, waveguide and detector devices. To form the masked substrates, stripes (ranging in width from 2 pm to 50 pm) were opened up in SiO2 by standard photolithography. The crystal growths were carried out at various substrate temperatures (ranging from 460 °C to 510 °C) and arsenic fluxes (V/lll ratios ranging from 1.2 to 3.4). The properties of the epitaxial layers were investigated by using such analytical techniques as photoluminescence, electroluminescence and transmission electron microscopy (TEM). Photoluminescence measurements performed on waveguide stripes of decreasing width reveal an increasing red-shift of the e1-hh1 transition in InGaAs wells. The maximum red-shift occurred when growing at a high substrate temperature and a low arsenic flux. For example, a decrease in slit width from 50 pm to 10 pm resulted in a 25 meV shift of the photoluminescence peak. From cross-sectional TEM measurements, the wavelength shift observed can be attributed primarily to an increase in thickness of the InGaAs well, due to incorporation of additional indium and gallium migrating from the material on the masked regions. The interfaces in the centre of the stripe region are defect free; however, stacking faults and thickness variations are evident 1-2 pm from the edges. These results are confirmed by scanning photoluminescence, in which the maximum intensity occurs at the centre of the stripe and decreases to zero at the edges. Mapping of the peak wavelength across the stripe reveals a diffusion profile, with the edges being additionally red shifted by 10 nm. Reactive ion etching of the edge and the polycrystalline material results in a much improved spectral photoluminescence scan, in both increased intensity of the bandgap peak and elimination of lower energy peaks assumed to be correlated with edge effects. Finally, a stripe contact light emitting device, with a single 50 A quantum well InGaAs/lnP structure, was fabricated and electrically pumped. The device exhibited spectral peak wavelength shifts between narrow stripes (10 pm) and wide stripes (50 pm) of 22 nm, similar to the value observed by photoluminescence studies. / Thesis / Master of Engineering (ME)

No description available.

THz spinduliuotės generavimas iš puslaidininkių paviršiaus turi didelį potencialą puslaidininkių fizikinėms savybėms tirti. Šis darbas skiriamas puslaidininkių tyrimams generuojant THz impulsus iš jų paviršių, apšviestų femtosekundiniais lazerio impulsais. THz spinduliuotė iš puslaidininkių paviršių gali būti generuojama dėl visos eilės fizikinių mechanizmų: paviršinio lauko ekranavimo, foto-Demberio efekto, optinio lyginimo, elektriniu lauku indukuoto optinio lyginimo, plazminių svyravimų, koherentinių fononų ir plazmonų. Tiriant THz spinduliuotės generacijos mechanizmus galima išmatuoti daug svarbių puslaidininkių parametrų, tokių kaip lūžio rodiklis, judris, krūvininkų gyvavimo trukmė, aukštesniųjų laidumo slėnių padėtys. Darbo metu tirti THz spinduliuotės generacijos puslaidininkio paviršiuje mechanizmai keičiant žadinimo sąlygas: aplinkos temperatūrą, magnetinį lauką, žadinančio lazerio bangos ilgį ir intensyvumą, bei impulso trukmę. Ištyrus visą eilę įvairių puslaidininkių nustatyta, kad geriausias THz spinduliuotės emiteris žadinant 800 nm bangos ilgio spinduliuote yra p-InAs. Pirmą kartą THz žadinimo spektroskopijos metodu tiesiogiai išmatuoti tarpslėniniai atstumai InxGa1-xAs , InAs ir InSb bandiniuose. / Generation of terahertz radiation from semiconductor surfaces has great potential for investigation of physical properties of semiconductors. This work focuses on the semiconductor research when generating terahertz pulses from a variety of semiconductor surfaces. THz radiation from semiconductor surfaces can be generated on a whole range of physical mechanisms: the surface field screening, photo-Dember effect, the optical rectification, electric field induced optical rectification, plasma oscillations, coherent phonons and plasmons. A number of important semiconductor parameters such as refractive index, mobility, carrier relaxation time and higher conductivity valley positions can be measured using THz generation from semiconductor surface technique. In this work THz radiation generation mechanisms were investigated when changing excitation conditions: ambient temperature, magnetic field, laser wavelength and intensity, pulse duration. After tests with variety different semiconductors it was found that p-InAs is the best surface emitter when excitation laser wavelength is 800 nm. Using THz excitation spectroscopy the intervalley distances were measured directly, for the first time, in two InxGa1-xAs, InAs and InSb samples.

Generation of terahertz radiation from semiconductor surfaces has great potential for investigation of physical properties of semiconductors. This work focuses on the semiconductor research when generating terahertz pulses from a variety of semiconductor surfaces. THz radiation from semiconductor surfaces can be generated on a whole range of physical mechanisms: the surface field screening, photo-Dember effect, the optical rectification, electric field induced optical rectification, plasma oscillations, coherent phonons and plasmons. A number of important semiconductor parameters such as refractive index, mobility, carrier relaxation time and higher conductivity valley positions can be measured using THz generation from semiconductor surface technique. In this work THz radiation generation mechanisms were investigated when changing excitation conditions: ambient temperature, magnetic field, laser wavelength and intensity, pulse duration. After tests with variety different semiconductors it was found that p-InAs is the best surface emitter when excitation laser wavelength is 800 nm. Using THz excitation spectroscopy the intervalley distances were measured directly, for the first time, in two InxGa1-xAs, InAs and InSb samples. / THz spinduliuotės generavimas iš puslaidininkių paviršiaus turi didelį potencialą puslaidininkių fizikinėms savybėms tirti. Šis darbas skiriamas puslaidininkių tyrimams generuojant THz impulsus iš jų paviršių, apšviestų femtosekundiniais lazerio impulsais. THz spinduliuotė iš puslaidininkių paviršių gali būti generuojama dėl visos eilės fizikinių mechanizmų: paviršinio lauko ekranavimo, foto-Demberio efekto, optinio lyginimo, elektriniu lauku indukuoto optinio lyginimo, plazminių svyravimų, koherentinių fononų ir plazmonų. Tiriant THz spinduliuotės generacijos mechanizmus galima išmatuoti daug svarbių puslaidininkių parametrų, tokių kaip lūžio rodiklis, judris, krūvininkų gyvavimo trukmė, aukštesniųjų laidumo slėnių padėtys. Darbo metu tirti THz spinduliuotės generacijos puslaidininkio paviršiuje mechanizmai keičiant žadinimo sąlygas: aplinkos temperatūrą, magnetinį lauką, žadinančio lazerio bangos ilgį ir intensyvumą, bei impulso trukmę. Ištyrus visą eilę įvairių puslaidininkių nustatyta, kad geriausias THz spinduliuotės emiteris žadinant 800 nm bangos ilgio spinduliuote yra p-InAs. Pirmą kartą THz žadinimo spektroskopijos metodu tiesiogiai išmatuoti tarpslėniniai atstumai InxGa1-xAs , InAs ir InSb bandiniuose.