Auswahl der wissenschaftlichen Literatur zum Thema „GaAs-4H“

Recently, polytypism has been observed in nanowires in materials, for which normally only one crystal structure is stable. For example, GaAs, nanowires can have wurtzite or mixed zincblende/wurtzite. Here we provide band structure parameters for wurzite and 4H GaAs and use them for modeling the nanowire electronic states. The band gap, crystal field splitting, and its strain dependence, as well as the effective mass parameters are calculated using the quasiparticle self-consistent GW method. The nanowire electronic states are obtained in the envelope function approximation within a simplified cylindrical model. The crystal field splitting of the wurtzite GaAs valence band is found to be 180 meV while in 4H-GaAs it is less than half 69 meV, suggesting a downward bowing as function of hexagonality. The conduction band minimum at Γ changes symmetry character under strain. We discuss the consequences for nanowires and determine the conditions under which a polarization reversal of photoluminescence can occur from mostly perpendicular to parallel to the wire.

Abstract In this paper investigation on electrical and thermal performance of the AlGaAs/GaAs HEMT device is carried out by comparing the device grown on substrates like 4H-SiC and Sapphire. The investigation was carried out based on Silvaco TCAD Atlas simulation. The DC characteristics of the device with varying ambient temperature were evaluated. A deterioration of drain current from 0.9 mA to 0.5 mA is observed as temperature rises from 300K to 500K on 4H-SiC substrate. The HEMT grown on 4H-SiC substrate has a high power dissipation, resulting in reduced temperature compared to sapphire substrate. This increases the lifetime of the device by 1000s of hours and also its overall performance. The HEMT proposed here is found to have an electrically and thermally optimal performance on 4H-SiC substrate than on sapphire

This paper presents a comprehensive assessment of the performance of on-chip circularly polarized (CP) circular loop antennas that have been designed and fabricated to operate in the Q/V frequency band. The proposed antenna design incorporates two concentric loops, with the outer loop as the active element and the inner loop enhancing the CP bandwidth. The study utilizes gallium arsenide (GaAs) and silicon carbide (4H-SiC) semiconductor wafer substrates. The measured results highlight the successful achievement of impedance matching at 40 GHz and 44 GHz for the 4H-SiC and GaAs substrates, respectively. Furthermore, both cases yield an axial ratio (AR) of less than 3 dB, with variations in bandwidths and frequency bands contingent upon the dielectric constant of the respective substrate material. Moreover, the outcomes confirm that utilizing 4H-SiC substrates results in a significantly higher radiation efficiency of 95%, owing to lower substrate losses. In pursuit of these findings, a 4-element circularly polarized loop array antenna has been fabricated for operation at 40 GHz, employing a 4H-SiC wafer as a low-loss substrate. The results underscore the antenna’s remarkable performance, exemplified by a broadside gain of approximately 9.7 dBic and a total efficiency of circa 92%. A close agreement has been achieved between simulated and measured results.

AbstractSignificant progress has been made in the development of SiC metal semiconductor field-effect transistors (MESFETs) and monolithic microwave integrated-circuit (MMIC) power amplifiers for high-frequency power applications. Three-inch-diameter high-purity semi-insulating 4H-SiC substrates have been used in this development, enabling high-volume fabrication with improved performance by minimizing surface- and substrate-related trapping issues previously observed in MESFETs. These devices exhibit excellent reliability characteristics, with mean time to failure in excess of 500 h at a junction temperature of 410°C. A sampling of these devices has also been running for over 5000 h in an rf high-temperature operating-life test, with negligible changes in performance. High-power SiC MMIC amplifiers have also been demonstrated with excellent yield and repeatability. These MMIC amplifiers show power performance characteristics not previously available with conventional GaAs technology. These developments have led to the commercial availability of SiC rf power MESFETs and to the release of a foundry process for MMIC fabrication.

Different semiconductor materials have been used for the fabrication of PIN diodes such as Si, Ge, GaAs, SiC-3C, SiC-4H, and InAs. These different semiconductor materials show different characteristics and advantages such as SiC-4H is ultrafast switch. But, when flexible polymers composites like Si-nanomembranes, polyethylene terephthalate (PET), and biodegradable polymer composite like carbon nanotubes (CNT) are used for fabrication, the device has the capability to switch from rigid electronic devices to flexible and wearable electronic devices. These polymer composites’ outstanding characteristics like conductivity, charge selectivity, flexibility, and lightweight make them eligible for their selection in fabrication process for wearable electronics devices. In this article, the performance of PIN diodes (BAR64-02) as an RF switch is investigated from 1 to 10 GHz. PIN diodes can control large amounts of RF power at very low DC voltage, implying their suitability for RF applications. In this paper, the benefit of using plastic polymer composites for the fabrication of PIN diodes, capacitors, and antennas is thoroughly described. Along with this, individual characterization, fabrication, and testing of all biasing components are also done to analyze the individual effect of each biasing component on the performance of PIN diodes. The complete biasing circuitry for the PIN diode is modeled in the HFSS software. When a PIN diode is inserted in between 50 Ω microstrip line, it introduces 1 dB insertion loss and 20 dB isolation loss from 1 to 7 GHz. Finally, a PIN diode is integrated in a reconfigurable antenna to study the actual effect. The transmission loss in the RF signal is nearly 1 dB from 1 to 7 GHz in the presence of biasing components.

Le silicium et le germanium, qui cristallisent dans la structure cubique du diamant (notée 3C), ont été les piliers de l'industrie électronique grâce à leurs propriétés intrinsèques. Néanmoins, l'ingénierie des phases cristallines métastables a émergé comme une méthode puissante pour ajuster les structures de bande électronique, ouvrant la voie à de nouvelles fonctionnalités tout en maintenant une compatibilité chimique. Notamment, le Ge dans la phase hexagonale 2H présente un gap direct de 0,38 eV. L'alliage SixGe(1-x)-2H présente une émission lumineuse intense avec une longueur d'onde modulable entre 1,8 µm et 3,5 µm, selon la concentration en silicium (40 % à 0 %). Ces propriétés positionnent SixGe(1-x)-2H comme un « matériau miracle» parmi les semi-conducteurs du groupe IV, avec des applications prometteuses dans l'émission lumineuse dans le moyen infrarouge et la détection sur des plateformes en silicium.Malgré les progrès récents, la synthèse de volumes importants de Ge-2H de haute qualité reste un défi. Jusqu'à présent, Le Ge-2H a été synthétisé sous forme de nanodomaines issus de transformations de phase induites par cisaillement, de nanofils cœur/enveloppe et de nanobranches. Ces approches limitent les volumes actifs et la fabrication évolutive de dispositifs. La synthèse de couches planaires de SixGe(1-x)-2H de haute qualité, avec un dopage contrôlé, est essentielle pour permettre une intégration optimale.Cette thèse vise à ouvrir la voie à la synthèse de couches planes de Ge hexagonal en utilisant l'épitaxie en phase vapeur sous ultra-haut vide (UHV-VPE) sur des substrats hexagonaux plan-m du groupe II-VI, tels que CdS-2H et ZnS-4H. Les travaux incluent le développement de techniques de préparation de surface pour les composés II-VI et des études détaillées sur la formation de structures hexagonales dans des matériaux tels que GaAs-4H, ZnS-2H via MOCVD, et le Ge dans les phases hexagonales 2H et 4H.Une étape préliminaire cruciale a consisté à préparer les surfaces des substrats, car leur qualité impacte directement celle des couches épitaxiées. La préparation des surfaces a inclus un polissage mecano-chimique avec une solution de Br2-MeOH pour éliminer les contaminants de surface. Les défis liés aux propriétés thermiques des substrats CdS-2H et ZnS-4H ont été abordés, notamment la désorption des composés II-VI et la formation de « negative whiskers » au-dessus de 500°C.La croissance épitaxiale par UHV-VPE a posé des contraintes de sélectivité sur les substrats II-VI, ce qui a conduit à explorer des configurations alternatives de croissance, telles que l'utilisation de couches buffer. Cette thèse présente la première synthèse d'une couche de GaAs dans la structure hexagonale 4H par épitaxie sur un substrat ZnS-4H plan-m, ainsi qu'une première caractérisation des défauts d'empilement basal dans cette couche. La faisabilité de la synthèse de Ge sur GaAs-4H a également été étudiée. Une part importante du travail a été consacrée à la croissance sur les substrats CdS-2H, démontrant la première couche de Ge avec des régions nanométriques de Ge-2H, offrant une preuve de concept pour la réplication de structures Ge-2H sur des surfaces II-VI sur plan-m. L'optimisation du processus a conduit au développement de couches tampons ZnS-2H sur CdS-2H via MOCVD. Une étude approfondie a montré que la température de croissance impacte fortement la qualité cristalline des substrats CdS. Les couches de ZnS cultivées à 360°C ont révélé une structure hexagonale pure avec une orientation épitaxiale optimale. La relaxation des contraintes s'est produite via des dislocations de réseau à l'interface, en raison des désaccords de maille de 7,63 % et 6,83 % le long des axes a et c, formant des défauts d'empilement basal et prismatique sur les plans {112 ̅0}. Enfin, pour appuyer notre étude, cette thèse présente des preuves démontrant la synthèse d'une couche de Ge avec une phase hexagonale partielle
Silicon and Germanium crystallizing in the cubic diamond (denoted 3C) structure, have been the cornerstone of the electronic industry due to their inherent properties. However, metastable crystal phase engineering has emerged as a powerful method for tuning electronic band structures and conduction properties, enabling new functionalities while maintaining chemical compatibility. Notably, Germanium within the hexagonal 2H phase exhibits a direct bandgap of 0.38 eV. The alloy SixGe(1-x)-2H demonstrates strong light emission with a tunable wavelength ranging from 1.8 µm to 3.5 µm, depending on silicon concentration (40% to 0%). These properties position SixGe(1-x)-2H as a "holy grail material" among group IV semiconductors, with promising applications in mid-infrared light emission (e.g., LEDs and lasers) and detection on silicon platform.Despite recent progress, synthesizing large volumes of high-quality Ge-2H remains a challenge. Until now, Ge-2H has been limited to nanostructures, including nanodomains formed by shear-induced phase transformation, core/shell nanowires, and nanobranches. These approaches restrict active volumes, hindering basic property investigation and scalable device manufacturing. Achieving high-quality planar crystals with controlled doping is essential for advancing SixGe(1-x)-2H integration.This thesis aims to pioneer the synthesis of planar layers of hexagonal Ge using Ultra High Vacuum - Vapor Phase Epitaxy (UHV-VPE) on hexagonal m-plane II-VI substrates such as CdS-2H and ZnS-4H. The work includes developing surface preparation techniques for II-VI compounds and conducting detailed studies on hexagonal structure formation in materials such as GaAs-4H, ZnS-2H (grown via Metal-Organic Chemical Vapor Deposition, MOCVD), and Ge in both 2H and 4H hexagonal phases.A crucial preliminary step involved preparing substrate surfaces, as their quality directly impacts the crystalline quality of the epitaxial layers. Surface preparation included chemical-mechanical polishing with a Br2-MeOH solution to remove surface contaminants, confirmed through XPS analysis. Challenges related to the thermal properties of CdS-2H and ZnS-4H substrates were addressed, including desorption of II-VI compounds and the formation of negative whiskers above 500°C.Epitaxial growth by UHV-VPE posed selectivity constraints on II-VI substrates, prompting the exploration of alternative growth configurations, such as using buffer template layers. This thesis presents the first synthesis of a GaAs layer in the 4H hexagonal structure grown by epitaxy on ZnS-4H m-plane substrate, along with a first characterization of basal stacking faults (BSFs) in this layer. The feasibility of synthesizing Ge on GaAs-4H was also investigated. A significant part of the work was dedicated to growth on the CdS-2H substrates, demonstrating the first Ge layer with nanoscale regions of Ge-2H epitaxy, providing proof of concept for structure replication of Ge-2H on II-VI m-plane surfaces. However, amorphous and highly defective regions were also observed. Process optimization led to the development of ZnS-2H template layers on CdS-2H using MOCVD, circumventing constraints of direct growth on CdS. A thorough investigation of growth regimes revealed a strong impact of growth temperature on the CdS substrate surface, significantly influencing crystalline quality. m-plane ZnS layers grown at 360°C exhibited a pure hexagonal structure with excellent epitaxial orientation relative to CdS-WZ substrates. Strain relaxation occurred through misfit dislocations at the interface due to lattice mismatches of 7.63% and 6.83% along the a- and c-axes, forming basal and prismatic stacking faults on {11-20} planes. Finally, as further proof of concept, the thesis presents evidence supporting the synthesis of a Ge layer with a partial hexagonal phase