Properties of two‐dimensional electron gas in AlGaN/GaN HEMT structures determined by cavity‐enhanced THz optical Hall effect

Armakavicius, Nerijus; Chen, Jr-Tai; Hofmann, Tino; Knight, Sean; Kühne, Philipp; Nilsson, Daniel; Forsberg, Urban; Janzén, Erik; Darakchieva, Vanya

doi:10.1002/pssc.201510214

Cited by 24 publications

(18 citation statements)

References 11 publications

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“…The 2DEG effective mass parameter is somewhat higher than the bulk GaN electron mass of 0.232m 0 [63], which is in agreement with previous reports [55,59,64]. The observed difference could be attributed to a penetration of the 2DEG wavefunction into the AlGaN barrier layer that was shown to be strongly affected by temperature [55] and it is further discussed in Ref.…”

Section: Terahertz Optical Hall Effect (Thz-ohe)supporting

confidence: 90%

“…The observed difference could be attributed to a penetration of the 2DEG wavefunction into the AlGaN barrier layer that was shown to be strongly affected by temperature [55] and it is further discussed in Ref. [59].…”

Section: Terahertz Optical Hall Effect (Thz-ohe)mentioning

confidence: 93%

“…The OHE allows for detection of three free charge carrier parameters, charge density, charge mobility and effective mass [54][55][56][57][58]. The magnitude of the OHE birefringence can be further tuned by adding a cavity with varying thickness on the backside of a (transparent) sample [42,59,60].…”

Section: Terahertz Optical Hall Effect (Thz-ohe)mentioning

confidence: 99%

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Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

Kühne

Armakavicius

Stanishev

et al. 2018

IEEE Trans. THz Sci. Technol.

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Abstract-We present a terahertz (THz) frequency-domain spectroscopic (FDS) ellipsometer design which suppresses formation of standing waves by use of stealth technology approaches. The strategy to suppress standing waves consists of three elements geometry, coating and modulation. The instrument is based on the rotating analyzer ellipsometer principle and can incorporate various sample compartments, such as a superconducting magnet, in-situ gas cells or resonant sample cavities, for example. A backward wave oscillator and three detectors are employed, which permit operation in the spectral range of 0.1-1 THz (3.3-33 cm −1 or 0.4-4 meV). The THz frequency-domain ellipsometer allows for standard and generalized ellipsometry at variable angles of incidence in both reflection and transmission configurations. The methods used to suppress standing waves and strategies for an accurate frequency calibration are presented. Experimental results from dielectric constant determination in anisotropic materials, and free charge carrier determination in optical Hall effect, resonant-cavity enhanced optical Hall effect and in-situ optical Hall effect experiments are discussed. Examples include silicon and sapphire optical constants, free charge carrier properties of two dimensional electron gas in group-III nitride high electron mobility transistor structure, and ambient effects on free electron mobility and density in epitaxial graphene.

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Section: Terahertz Optical Hall Effect (Thz-ohe)supporting

confidence: 90%

Section: Terahertz Optical Hall Effect (Thz-ohe)mentioning

confidence: 93%

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Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

Kühne

Armakavicius

Stanishev

et al. 2018

IEEE Trans. THz Sci. Technol.

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“…It has been shown that the use of a backside cavity with a highly reflective backside surface can enhance the OHE in HEMT structures and EG, as a result of the formation of Fabri-Pérot modes, within the sample-cavity system [37][38][39]. An optical scheme of the cavity-enhanced (CE)-OHE measurement for a sample containing a transparent substrate and a conductive layer on top is shown in Figure 1.3.…”

Section: Cavity-enhanced Optical Hall Effectmentioning

confidence: 99%

Study of novel electronic materials by mid-infrared and terahertz optical Hall effect

Armakavicius¹

2017

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Development of silicon based electronics have revolutionized our every day life during the last three decades. Nowadays Si based devices operate close to their theoretical limits that is becoming a bottleneck for further progress. In particular, for the growing field of high frequency and high power electronics, Si cannot offer the required properties. Development of materials capable of providing high current densities, carrier mobilities and high breakdown fields is crucial for a progress in state of the art electronics. Epitaxial graphene grown on semi-insulating silicon carbide substrates has a high potential to be integrated in the current planar device technologies. High electron mobilities and sheet carrier densities make graphene extremely attractive for high frequency analog applications. One of the remaining challenges is the interaction of epitaxial graphene with the substrate. Typically, much lower free charge carrier mobilities, compared to free standing graphene, and doping, due to charge transfer from the substrate, is reported. Thus, a good understanding of the intrinsic free charge carriers properties and the factors affecting them is very important for further development of epitaxial graphene. III-group nitrides have been extensively studied and already have proven their high efficiency as light sources for short wavelengths. High carrier mobilities and breakdown electric fields were demonstrated for III-group nitrides, making them attractive for high frequency and high power applications. Currently, In-rich InGaN alloys and AlGaN/GaN high electron mobility structures are of high interest for the research community due to open fundamental questions. Electrical characterization techniques, commonly used for the determination of free charge carrier properties, require good ohmic and Schottky contacts, which in certain cases can be difficult to achieve. Access to electrical properties of buried conductive channels in multilayered structures requires modification of samples and good knowledge of the electrical properties of all electrical contact within the structure. Moreover, the use of electrical contacts to electrically characterize two-dimensional electronic materials, such as graphene, can alter their intrinsic properties. Furthermore, the determination of effective mass parameters commonly employs cyclotron resonance and Shubnikov-de Haas oscillations measurements, which require long scattering times of free charge carriers, high magnetic fields and low temperatures. The optical Hall effect is an external magnetic field induced optical anisotropy in conductive layers due to the motion of the free charge carriers under the influence of the Lorentz force, and is equivalent to the electrical Hall effect at optical frequencies. The optical Hall effect can be measured by generalized ellipsometry and provides a powerful method for the determination of free charge carrier properties in a non-destructive and contactless manner. In principle, a single optical Hall effect measurement can provide quan...

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“…3.13). The physical cause of the enhancement is the radiation reflected back in by the magnet surface undergoing further polarization-state changes when passing the magneto-optic birefringent sample constituent [165,166]. THz OHE allows performing an OHE measurements a room temperature and with relatively low-field permanent magnet.…”

Section: Cavity-enhanced and In-situ Cavity-enhanced Thz Optical Hallmentioning

confidence: 99%

Structural and Electronic Properties of Graphene on 4H- and 3C-SiC

Bouhafs¹

2016

Linköping Studies in Science and Technology. Dissertations

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Je dédie cette thèse pour ceux qui sont très loin de moi et très prochesà mon coeur:Pour celle qui vient de l'île des rêves et qui a changè ma vie au plus beau rêve.Pour celle que je dois ma vie. Pour ma famille.Pour ceux qui ne perdent jamais la foi en l'humanité. v ABSTRACTGraphene is a one-atom-tick carbon layer arranged in a honeycomb lattice. Graphene was first experimentally demonstrated by Andre Geim and Konstantin Novoselov in 2004 using mechanical exfoliation of highly oriented pyrolytic graphite (exfoliated graphene flakes), for which they received the Nobel Prize in Physics in 2010. Exfoliated graphene flakes show outstanding electronic properties, e.g., very high free charge carrier mobility parameters and ballistic transport at room temperature. This makes graphene a suitable material for next generation radio-frequency and terahertz electronic devices. Such applications require fabrication methods of large-area graphene compatible with electronic industry. Graphene grown by sublimation on silicon carbide (SiC) offers a viable route towards production of large-area, electronic-grade material on semi-insulating substrate without the need of transfer. Despite the intense investigations in the field, uniform wafer-scale graphene with very high-quality that matches the properties of exfoliated graphene has not been achieved yet. The key point is to identify and control how the substrate affects graphene uniformity, thickness, layer stacking, structural and electronic properties. Of particular interest is to understand the effects of SiC surface polarity and polytype on graphene properties in order to achieve large-area material with tailored properties for electronic applications. The main objectives of this thesis are to address these issues by investigating the structural and electronic properties of epitaxial graphene grown on 4H-SiC and 3C-SiC substrates with different surface polarities.The first part of the thesis includes a general description of the properties of graphene, bilayer graphene and graphite. Then, the properties of epitaxial graphene on SiC by sublimation are detailed. The experimental techniques used to characterize graphene are described. A summary of all papers and contribution to the field is presented at the end of Part I. Part II consists of seven papers.Paper I reports on the structural, vibrational, and dielectric function properties of graphene grown on the C-face of 4H-SiC(000 − 1) with surface defects. We have shown that the average number of graphene layers, the size of the domains with uniform thickness and the crystallite size increase with the increase of temperature. This improved graphene quality is attributed to an enhanced sublimation of Si from the SiC and to the elimination of SiC surface defects by surface restructuring during the sublimation growth. Central result of the paper is the transition from decoupled to Bernal stacked graphene layers with the increase in growth temperature, which is explained by a competition between growth mechanisms. We also determin...

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Properties of two‐dimensional electron gas in AlGaN/GaN HEMT structures determined by cavity‐enhanced THz optical Hall effect

Cited by 24 publications

References 11 publications

Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

Study of novel electronic materials by mid-infrared and terahertz optical Hall effect

Structural and Electronic Properties of Graphene on 4H- and 3C-SiC

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