Terahertz optical-Hall effect characterization of two-dimensional electron gas properties in AlGaN/GaN high electron mobility transistor structures

Schöche, S.; Shi, Jonathan; Boosalis, A.; Kühne, Philipp; Herzinger, C. M.; Woollam, John A.; Schaff, William J.; Eastman, L.F.; Schubert, M.; Hofmann, Tino

doi:10.1063/1.3556617

Cited by 27 publications

(21 citation statements)

References 23 publications

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“…In order to derive the free charge carrier density and mobility parameters from the plasma frequency and broadening parameters one needs the effective mass parameters. Unless magnetic fields are exploited and the optical Hall effect can be measured [93,[95][96][97][98][99][100][101], long-wavelength ellipsometry requires these parameters from auxiliary investigations.…”

Section: -11mentioning

confidence: 99%

Anisotropy, phonon modes, and free charge carrier parameters in monoclinicβ-gallium oxide single crystals

et al. 2016

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We derive a dielectric function tensor model approach to render the optical response of monoclinic and triclinic symmetry materials with multiple uncoupled infrared and far-infrared active modes. We apply our model approach to monoclinic β-Ga 2 O 3 single-crystal samples. Surfaces cut under different angles from a bulk crystal, (010) and (201), are investigated by generalized spectroscopic ellipsometry within infrared and far-infrared spectral regions. We determine the frequency dependence of 4 independent β-Ga 2 O 3 Cartesian dielectric function tensor elements by matching large sets of experimental data using a point-by-point data inversion approach. From matching our monoclinic model to the obtained 4 dielectric function tensor components, we determine all infrared and far-infrared active transverse optic phonon modes with A u and B u symmetry, and their eigenvectors within the monoclinic lattice. We find excellent agreement between our model results and results of density functional theory calculations. We derive and discuss the frequencies of longitudinal optical phonons in β-Ga 2 O 3 . We derive and report density and anisotropic mobility parameters of the free charge carriers within the tin-doped crystals. We discuss the occurrence of longitudinal phonon plasmon coupled modes in β-Ga 2 O 3 and provide their frequencies and eigenvectors. We also discuss and present monoclinic dielectric constants for static electric fields and frequencies above the reststrahlen range, and we provide a generalization of the Lyddane-Sachs-Teller relation for monoclinic lattices with infrared and far-infrared active modes. We find that the generalized Lyddane-Sachs-Teller relation is fulfilled excellently for β-Ga 2 O 3 .

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Section: -11mentioning

confidence: 99%

Anisotropy, phonon modes, and free charge carrier parameters in monoclinicβ-gallium oxide single crystals

et al. 2016

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“…22,[25][26][27][28] Later, OHE experiments were conducted in the terahertz (THz) spectral range, 29 but were limited to room temperature and low magnetic fields (B ≤ 1.8 T). [30][31][32][33] Since the magnitude of the OHE depends on the magnetic field strength, higher magnetic fields facilitate the detection of the OHE. Furthermore, the sensitivity to the OHE is greatly enhanced by phonon mode coupling, 34,35 surface guided waves 27 and Fabry-Pérot interferences.…”

Section: Introductionmentioning

confidence: 99%

Invited Article: An integrated mid-infrared, far-infrared, and terahertz optical Hall effect instrument

Kühne

Herzinger

Schubert

et al. 2014

Review of Scientific Instruments

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We report on the development of the first integrated mid-infrared, far-infrared and terahertz optical Hall effect instrument, covering an ultra wide spectral range from 3 cm −1 to 7000 cm −1 (0.1-210 THz or 0.4-870 meV). The instrument comprises four sub-systems, where the magneto-cryostat-transfer sub-system enables the usage of the magneto-cryostat sub-system with the mid-infrared ellipsometer sub-system, and the far-infrared/terahertz ellipsometer sub-system. Both ellipsometer sub-systems can be used as variable angleof-incidence spectroscopic ellipsometers in reflection or transmission mode, and are equipped with multiple light sources and detectors. The ellipsometer sub-systems are operated in polarizer-sample-rotating-analyzer configuration granting access to the upper left 3 × 3 block of the normalized 4 × 4 Mueller matrix. The closed cycle magneto-cryostat sub-system provides sample temperatures between room temperature and 1.4 K and magnetic fields up to 8 T, enabling the detection of transverse and longitudinal magnetic field-induced birefringence. We discuss theoretical background and practical realization of the integrated mid-infrared, far-infrared and terahertz optical Hall effect instrument, as well as acquisition of optical Hall effect data and the corresponding model analysis procedures. Exemplarily, epitaxial graphene grown on 6H -SiC, a tellurium doped bulk GaAs sample and an AlGaN/GaN high electron mobility transistor structure are investigated. The selected experimental datasets display the full spectral, magnetic field and temperature range of the instrument and demonstrate data analysis strategies. Effects from free charge carriers in two dimensional confinement and in a volume material, as well as quantum mechanical effects (inter-Landau-level transitions) are observed and discussed exemplarily.

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“…In general, this birefringence leads to polarization mode coupling which is conveniently detected by generalized ellipsometry at oblique angle of incidence and at terahertz (THz) frequencies, for example. THz-OHE has recently been demonstrated as non-contact and therefore valuable tool for the investigation of free charge carrier properties in semiconductor heterostructures [2][3][4][5][6][7][8][9]. Previous instrumental approaches, discussed more detailed in Refs.…”

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confidence: 99%

“…The experimental MIR-SE and THz-OHE data sets were analyzed simultaneously using an optical model composed of eight phases including a AlInN top layer/2DEG/AlN spacer/GaN buffer/Al 2 O 3 substrate/air gap/Ni cavity surface [7]. Nonlinear regression methods where used to match the lineshape of experimental and optical model calculated data as close as possible by varying relevant model parameters using parameterized model dielectric functions [13].…”

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Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies

et al. 2015

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The effect of a tunable, externally coupled Fabry-Pérot cavity to resonantly enhance the optical Hall effect signatures at terahertz frequencies produced by a traditional Drude-like two-dimensional electron gas is shown and discussed in this communication. As a result, the detection of optical Hall effect signatures at conveniently obtainable magnetic fields, for example by neodymium permanent magnets, is demonstrated. An AlInN/GaN-based high electron mobility transistor structure grown on a sapphire substrate is used for the experiment. The optical Hall effect signatures and their dispersions, which are governed by the frequency and the reflectance minima and maxima of the externally coupled Fabry-Pérot cavity, are presented and discussed. Tuning the externally coupled Fabry-Pérot cavity strongly modifies the optical Hall effect signatures, which provides a new degree of freedom for optical Hall effect experiments in addition to frequency, angle of incidence and magnetic field direction and strength.The optical Hall effect (OHE) in semiconductor layer structures is the occurrence of magneto-optic birefringence detected in response to incident electromagnetic radiation, caused by movement of free charge carriers under the magnetic field-induced influence of the Lorentz force [1]. In general, this birefringence leads to polarization mode coupling which is conveniently detected by generalized ellipsometry at oblique angle of incidence and at terahertz (THz) frequencies, for example. THz-OHE has recently been demonstrated as non-contact and therefore valuable tool for the investigation of free charge carrier properties in semiconductor heterostructures [2][3][4][5][6][7][8][9]. Previous instrumental approaches, discussed more detailed in Refs. 2 and 9, rely on high magnetic fields provided either by conventional, water-cooled or superconducting, liquid He-cooled electromagnets resulting in comparably large and costly experimental setups. In general, OHE configurations capable of detecting signals at low and conveniently obtainable magnetic fields are desirable. The use of small magnetic fields for THz magnetooptic measurements was demonstrated recently by Ino et al. for bulk-like InAs [10]. Due to low effective mass and high charge carrier concentration, the low field still yielded large enough signals for detection. The signalto-noise separations of the OHE signatures depend on many factors, the most important are low effective mass, high mobility and high carrier density, but also crucial is the thickness of the physical layer that contains the charge carriers. The OHE signatures scale, in first approximation, linearly with the magnetic field amplitude. Hence, the first approach to detect OHE signatures in samples with very thin layers, or low-mobile, heavy-mass and low-density charge carriers where the OHE signatures are weak is to increase the magnetic field amplitude.In this communication, we demonstrate and exploit the enhancement of the OHE signal obtained from samples IG. 1. Schematic drawing of the beam pa...

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Terahertz optical-Hall effect characterization of two-dimensional electron gas properties in AlGaN/GaN high electron mobility transistor structures

Cited by 27 publications

References 23 publications

Anisotropy, phonon modes, and free charge carrier parameters in monoclinicβ-gallium oxide single crystals

Anisotropy, phonon modes, and free charge carrier parameters in monoclinicβ-gallium oxide single crystals

Invited Article: An integrated mid-infrared, far-infrared, and terahertz optical Hall effect instrument

Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies

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